HomeMy WebLinkAboutFebruary 03, 2014 AgendaAGENDA
CITY OF DENTON CITY COUNCIL
February 3, 2014
After determining that a quorum is present, the City Council of the City of Denton, Texas will
convene in a Work Session on Monday, February 3, 2014 at 11:30 a.m. in the Council Work
Session Room, 215 E. McKinney Street, Denton, Texas at which the following item will be
considered:
NOTE: A Work Session is used to explore matters of interest to one or more City Council
Members or the City Manager for the purpose of giving staff direction into whether or not such
matters should be placed on a future regular or special meeting of the Council for citizen input,
City Council deliberation and formal City action. At a Work Session, the City Council generally
receives informal and preliminary reports and information from City staff, officials, members of
City committees, and the individual or organization proposing council action, if invited by City
Council or City Manager to participate in the session. Participation by individuals and members
of organizations invited to speak ceases when the Mayor announces the session is being closed to
public input. Although Work Sessions are public meetings, and citizens have a legal right to
attend, they are not public hearings, so citizens are not allowed to participate in the session
unless invited to do so by the Mayor. Any citizen may supply to the City Council, prior to the
beginning of the session, a written report regarding the citizen's opinion on the matter being
explored. Should the Council direct the matter be placed on a regular meeting agenda, the staff
will generally prepare a final report defining the proposed action, which will be made available
to all citizens prior to the regular meeting at which citizen input is sought. The purpose of this
procedure is to allow citizens attending the regular meeting the opportunity to hear the views of
their fellow citizens without having to attend two meetings.
1. Receive a report, hold a discussion, and give staff direction concerning the 2013
mosquito season and upcoming 2014 season.
NOTE: The City Council reserves the right to adjourn into a Closed Meeting on any item on its
Open Meeting agenda consistent with Chapter 551 of the Texas Government Code, as amended,
including without limitation, Sections 551.071 - 551.086 of the Texas Open Meetings Act.
CERTIFICATE
I certify that the above notice of meeting was posted on the bulletin board at the City Hall of the
City of Denton, Texas, on the day of 2014 at o'clock
(a.m.) (p.m.)
CITY SECRETARY
NOTE: THE CITY OF DENTON COUNCIL WORK SESSION ROOM IS
ACCESSIBLE IN ACCORDANCE WITH THE AMERICANS WITH DISABILITIES ACT.
THE CITY WILL PROVIDE SIGN LANGUAGE INTERPRETERS FOR THE HEARING
IMPAIRED IF REQUESTED AT LEAST 48 HOURS IN ADVANCE OF THE SCHEDULED
MEETING. PLEASE CALL THE CITY SECRETARY'S OFFICE AT 349 -8309 OR USE
TELECOMMUNICATIONS DEVICES FOR THE DEAF (TDD) BY CALLING 1-800 -
RELAY-TX SO THAT A SIGN LANGUAGE INTERPRETER CAN BE SCHEDULED
THROUGH THE CITY SECRETARY'S OFFICE.
AGENDA INFORMATION SHEET
AGENDA DATE: Febwary 3, 2014
DEPARTMENT: Environmental Services and Sustainability
ACM: Howard Martin, 349 -8232
14v—
SUBJECT
Receive a report, hold a discussion, and give staff direction concerning the 2013 mosquito season
and upcoming 2014 season.
BACKGROUND
The City of Denton implemented the most extensive mosquito monitoring effort to date during
the 2013 season. Monitoring began on April 14, 2013 and continued approximately weekly
through November 19, 2013. Sixteen to twenty one traps were deployed each week, resulting in
a total of 539 "routine monitoring" traps for the season. All mosquitoes collected during
routine monitoring were shipped to the Texas Department of State Health Services (TDSHS) for
species identification and West Nile Vines (WNV) screening. In addition to routine monitoring,
the City of Denton and University of North Texas (UNT) researchers implemented a monitoring
and testing program using the Rapid Analyte Measurement Platform (RAMP). The RAMP
research was implemented as a pilot program to provide more rapid and flexible local West Nile
Vines screening capabilities. As stated above, mosquitoes collected during routine monitoring
events are shipped to the Texas Department of State Health Services (TDSHS) for species
identification and WNV screening. The services provided by the TDSHS are extremely
valuable to the overall monitoring program, but due to the State's workload can take a week or
more before results are finalized. The RAMP approach allows local researchers to produce
results within one day of collection. During the height of the mosquito season, the ability to
quickly analyze mosquitoes for WNV can help facilitate much more rapid and flexible local
responses. Monitoring for RAMP analyses began on May 7, 2013, and continued approximately
weekly through November 5, 2013, resulting in a total of approximately 231 traps for the season.
,Surveillance and Response efforts
Of the 770 total traps deployed, there were three samples collected that tested positive for WNV.
The first positive samples were collected on October 1, 2013 at Robson Ranch, and represented
one positive sample for routine monitoring and one for RAMP monitoring efforts. The third
positive sample was collected at the Pecan Creek Water Reclamation facility on October 22,
2013. There were two human WNV cases reported in Denton during the 2013 season. The first
case was reported on July 25t1' (onset date estimated as June 17t1') and the second case was
reported on October 16th (onset date estimated as September 30th). RAMP monitoring was
conducted in proximity to the human cases as soon as they were reported. The second human
case in October resulted in the declaration of Risk Level 5 for the City and the subsequent
decision to enact ground level spraying. The area surrounding the reported case was sprayed on
th
October 24
Page 2 of 5
During 2013, larviciding efforts within Denton were maintained at approximately the same level
of effort used in the 2012 season. During 2013, a total of 7,677 BTI applications were made by
Drainage, Parks, and Code enforcement personnel, and approximately 616 BTI briquettes were
distributed to citizens. During 2012, a total of 7,386 BTI applications were made, and
approximately 3,744 briquettes were provided to citizens. It is interesting to note that
substantially fewer citizens obtained BTI from the City in 2013 when compared to 2012.
Although somewhat speculative, this decrease is likely due to the much milder WNV season
experience in 2013 and the resulting overall decrease in media coverage for the issue. During
2013, staff also implemented limited use of Natular larvicides when applications required a
longer lasting alternative to BTL This larvicide appeared to work well for specialized
applications.
Following the 2012 season, Environmental Services staff worked with Technology Services to
improve the mosquito trap and spraying maps available on the City of Denton web site. Maps
used during the 2012 season were static images that did not allow users to effectively navigate
within the map image, zoom into particular areas, or obtain information not originally included
in the image. The previous maps also only indicated positive traps, and did not offer the
capability to see all of the trapping locations assessed during the season. The revised mapping
protocol used during 2013 now produces GIS based maps that offer navigation and zooming
capabilities, and trap maps that show current trap results as well as all trap results (positive and
negative) in selectable time sequences. The process by which addresses are extracted for
automated phone notification during spray events has also been much improved through the use
of the new system.
,Staff analyses of 2013 Mosquito Surveillance and Response Plan
Following the 2012 season, staff worked extensively with the City Council Committee on the
Environment and the City Council to revise the Mosquito Surveillance and Response Plan.
Revisions to the plan were completed prior to the start of the 2013 season. Staff has reviewed
the Plan following the 2013 season, and has made updates to statistics and some editorial
corrections. Aside from these minor changes, staff recommends no additional changes to the
plan. A copy of the 2014 Mosquito Surveillance and Response Plan is provided as Exhibit 2.
Analysis of 2012 mosquito and human WNV data
During the October 22, 2013 special called Council meeting to discuss Risk Level 5 and
spraying, the City Council directed staff to analyze the 2012 WNV positive trap data and WNV
positive human case data to determine if there were any relationships between trap results and
human cases. These analyses can become quite complex, due in part to exposure assumptions,
the time lag between human and mosquito results, and the need to establish some distance
(proximity) between trap locations and positive human cases. For the issue of proximity, staff
used a I mile distance surrounding the trap. The rationale for this approach is that the target
mosquito (Culex quinquefasciatus) adults are known to be weak flyers and do not tend to move
very far from the point of emergence. For the time lag issue, staff used a fairly simplistic
approach by considering a WNV positive human case reported at any time during the season
following a WNV positive trap as indicating a positive relationship. A similar approach was
used for negative traps, which resulted in counts for all cases where a trap location was negative
Page 3 of 5
all season and no human cases were reported within the distance criteria during the season.
Although the total number of WNV positive human cases in Denton during 2012 was 36, it is
important to note that not all positive human cases had a corresponding mosquito trap within one
mile. Using this approach, the following contingency table was constricted
Table 1. WNV Contingency Table
There are a number of different statistical analyses that can be run with contingency tables in this
form, most of which are some type of chi - square (or modified chi - square) analysis. Also, before
discussing the results, it is important to point out that 2012 was the worst WNV season
experienced in Denton, and the North Texas region was considered to be the epicenter of the
2012 WNV season for the entire United States. Even under these conditions, the incidence rate
of Denton's population was still 0.03 %, or about 1 person out of 3,255 people. It is also
important to point out that the trapping network was not set up with the intention of performing
analyses like this, and the analyses have underlying statistical assumptions (such as randomness)
that are questionable when applied to Denton's information. With this context in mind, the
results can be summarized as follows. Using the information from Table 1 above, a person does
have a significantly greater chance of contracting WNV if they live in proximity to mosquito trap
that has tested positive for WNV when compared to someone who lives in proximity to a trap
that has tested negative the entire season. The likelihood of someone contracting WNV is 14 to
73 percent higher, with an average of 59% higher, if they live in proximity to a positive trap
when compared to someone living within proximity to a trap that was negative the entire season.
In other words, assuming that in 2012 the incidence rate in the City of Denton for human WNV
cases of 1 person in every 3,255 people being diagnosed with the disease represented the average
incident rate in the City, then areas in proximity to a positive trap may have experienced an
average incidence rate of 1 person in every 2,050 people.
Current status of eyu1pment and inventory
The City of Denton has two trailer mounted Ultra -low volume (ULV) sprayers for ground based
spraying events. One sprayer is set up for continuous deployment, and one serves as a reserve in
case of equipment failure. However, it is important to note that having two sprayers also
provides the ability to conduct simultaneous spraying responses in different parts of the City.
Although Denton has not had the need to conduct simultaneous events spraying to date, the
capability exists to do so if needed. Because the 2013 season only had one spray event, the City
of Denton currently has an inventory of Duet adulticide and associated cleaning solution that is
sufficient for at least two large spray events. The current BTI inventory of 882 briquettes,
however, will need to be replenished prior to the start of the 2014 season.
Expenditures and bard et
The amount spent on mosquito control activities during 2013 season was approximately $38,230.
For comparison, 2012 total expenses were approximately $57,691. The majority of the
difference between the two years was due to spraying activities, including the purchase of
+ Human case w/ in 1 mile
No + human case w /in 1 mile
Trap Positive
19
8
Trap Negative
1
8
There are a number of different statistical analyses that can be run with contingency tables in this
form, most of which are some type of chi - square (or modified chi - square) analysis. Also, before
discussing the results, it is important to point out that 2012 was the worst WNV season
experienced in Denton, and the North Texas region was considered to be the epicenter of the
2012 WNV season for the entire United States. Even under these conditions, the incidence rate
of Denton's population was still 0.03 %, or about 1 person out of 3,255 people. It is also
important to point out that the trapping network was not set up with the intention of performing
analyses like this, and the analyses have underlying statistical assumptions (such as randomness)
that are questionable when applied to Denton's information. With this context in mind, the
results can be summarized as follows. Using the information from Table 1 above, a person does
have a significantly greater chance of contracting WNV if they live in proximity to mosquito trap
that has tested positive for WNV when compared to someone who lives in proximity to a trap
that has tested negative the entire season. The likelihood of someone contracting WNV is 14 to
73 percent higher, with an average of 59% higher, if they live in proximity to a positive trap
when compared to someone living within proximity to a trap that was negative the entire season.
In other words, assuming that in 2012 the incidence rate in the City of Denton for human WNV
cases of 1 person in every 3,255 people being diagnosed with the disease represented the average
incident rate in the City, then areas in proximity to a positive trap may have experienced an
average incidence rate of 1 person in every 2,050 people.
Current status of eyu1pment and inventory
The City of Denton has two trailer mounted Ultra -low volume (ULV) sprayers for ground based
spraying events. One sprayer is set up for continuous deployment, and one serves as a reserve in
case of equipment failure. However, it is important to note that having two sprayers also
provides the ability to conduct simultaneous spraying responses in different parts of the City.
Although Denton has not had the need to conduct simultaneous events spraying to date, the
capability exists to do so if needed. Because the 2013 season only had one spray event, the City
of Denton currently has an inventory of Duet adulticide and associated cleaning solution that is
sufficient for at least two large spray events. The current BTI inventory of 882 briquettes,
however, will need to be replenished prior to the start of the 2014 season.
Expenditures and bard et
The amount spent on mosquito control activities during 2013 season was approximately $38,230.
For comparison, 2012 total expenses were approximately $57,691. The majority of the
difference between the two years was due to spraying activities, including the purchase of
Page 4 of 5
sprayers, application costs, and chemicals. In addition, the RAMP pilot program was introduced
in 2013, and required approximately $17,700 for the initial purchase of the RAMP
instrumentation, associated equipment and reagents, and researcher funding. Staff recommends
continuing the RAMP program in the upcoming 2014 season, and anticipates costs will be
approximately $14,000.
Estimating future costs for mosquito surveillance and response is difficult due to the
uncertainties associated with spraying needs. Under the assumption of using the same level of
surveillance, RAMP testing, and larviciding as in 2013, and adding 10 -12 large spray events,
staff estimates that the following expenditures may be needed for the 2014 season. All expenses
should be considered approximate.
Table 2. 2014 Expenditures Estimates
Description
COST
estimate
UNT Monitoring Contract
$16,125
UNT RAMP program
$14,000
BTI purchase (6400 units)
$5,000
Pesticide / Cleaning fluid (use chemicals on hand and plan for 10 new events)
$3,000
Spraying contract ( approximately $300 -$500 per event, plan for 10 -12 events)
use existing
Sprayer re lacement fund (annual, based on replacement in 6 yrs = $16,600)
$2,800
Sprayer and trailer license, calibration, maintenance, and fuel
$1,000
TOTAL
$41,925
Total fixed costs (UNT programs and BTI purchase)
$35,125
Total variable / contingent costs (spraying 10 -12 large events
6,800
Staff suggests the following actions:
• Maintain the agreement with UNT to conduct mosquito surveillance activities at the
current level of effort (approximately $16,125).
• Maintain Bti purchases and applications at current levels.
• Continue the RAMP pilot program, including student support and reagent costs
(approximately $14,000).
• Maintain the Mosquito Surveillance and Response plan in its current form.
• The current mosquito surveillance and response program is funded by Water and
Wastewater budgets ($13,036 towards monitoring program). As outlined in Table 1, the
total expenditure for the 2014 season under the assumption of 10 -13 spray events will
require additional funding of approximately $28,889. If the spraying costs are not
funded at the beginning of the season and are instead considered for funding on an "as
needed" or emergency basis, the level of additional funding required will be
approximately $22,000.
• If funds are not fully expended for a given season, any remaining funds should be applied
to the upcoming season (with the exception of the sprayer replacement funds, which
should be allowed to accumulate until the estimated replacement cost is met). This
approach will reduce the amount needed from contingency funds in a particular fiscal
year if mosquito control activities were minimal in the previous season.
Page 5 of 5
Staff recommends considering adding the "contingency funded" mosquito response
activities outlined above as a formal supplemental budget item in the 2014 -2015 and
subsequent budgets.
OPTIONS
1. No further action
2. Direct staff to proceed with implementing suggestions as outlined above.
3. Table for future consideration
RECOMMENDATION
Staff recommends Option 2.
PRIOR ACTION/REVIEW (Council, Boards, Commissions)
None
FISCAL INFORMATION
The amount expended in the 2013 mosquito season was approximately $38,230.
The estimated cost for the 2014 season, under an assumption of no spraying, is $35,125.
The estimated cost for 2014 season is $41,925, under the assumption that 10 -12 large spray
events will be needed.
EXHIBIT
1. Presentation
2. Mosquito Surveillance and Response Plan, 2014 Final Draft
Respectfully prepared and submitted by,
Kenneth Banks.
Director, Environmental Services and Utility
Budgets
EXHIBIT 1
City of Denton
City Council
February 3, 2014
2013 Season Snapshot
• Routine monitoring
— Started April 14, ended Nov. 19
— 16 -20 traps per week, 539 total for season
• Rapid Analyte Measurement Program (RAMP)
— Started May 7, ended Nov. 5
— 8 -10 traps per week, 231 total for season
• Total of approximately 770 traps for the season
• Three positive tests: Two at Robson Ranch Oct.
1, and one at Pecan Creek WRF Oct. 22
2013 Season Snapshot
• Human cases:
— Two reported, July 25 and October 16
— October 16 resulted in Risk Level 5 and special
called Council session to consider spraying
— Area around second case sprayed on October 24
• RAMP Pilot Program evaluation
— Ability to analyze in 1 day (TDSHS 7+ days)
— Allowed rapid monitoring around human cases
— Provided additional monitoring and flexibility
— Staff perspective: program successful
2013 Season Snapshot
• Larviciding:
— 7,677 BTI applications, some Natular
— 616 briquettes provided to citizens
— 2012 (comparison): 7,386 BTI, 3,744 to citizens
• Public Information
— Spray and Trap Maps in prior years were "static"
— Maps improved for 2013, images are GIS, allow
users to navigate, current and historical trap data
available. Address and callout extraction is easier.
— Public Communication provided excellent support.
Mosquito Surveillance
and Response Plan
• Substantial changes discussed with Council
following 2012 season
• Changes implemented prior to 2013 season,
and worked well
• Staff has reviewed the plan and has updated
statistics and made minor editorial changes
• Staff recommends no changes for 2014 season
Analysis of mosquito /human cases
• During 10 -22 -13 Special Called meeting,
council asked staff to analyze relationships
between human cases and trap data for 2012
• Complications include exposure assumptions,
spraying activity impacts, time lag, and trap
distance.
• Monitoring network was not designed for this
kind of analysis, so possible violation of
underlying assumptions of statistical methods
(randomness, independence of variables, etc)
Analysis of mosquito /human
cases
• Proximity issue — target mosquito is a weak
flyer, used a distance of < 1 mile
• Time lag
— positive
relationship
if + result
mosquito
observed
in a trap and
human case
was reported in proximity at any point
during remainder of the season
WNV Contingency table
Trap positive 19 8
Trap negative 1 8
Results
• In 2012, higher risk of contracting "V if one
lived < 1 mile of a + trap, compared to living
near a trap that was negative for all events
• Likelihood was 14 — 73% higher, with an
average of 59%.
• Assuming 2012 average incident rate was 1 in
3,255, then 59% increase is 1 in 2,050 people
• Caveat: this approach is "stretching" the
statistical test assumptions of randomness and
independence, and ignores spray effects
Equipment and inventory status
• 2 ULV sprayers — one in
service, one backup.
Units have been very
reliable
• Enough chemicals for 4 -5
spray events.
• BTI inventory is low and
will be replenished for
next season
Expenditures and Estimates
2012
$57,691
2013
$38,230
Description
2014
estimate
UNT Monitoring Contract
$16,125
UNT RAMP program
$14,000
BTI purchase (6400 units)
$5,000
Pesticide / Cleaning fluid (use chemicals on hand and plan for 10 new events)
$3,000
Spraying contract ( approximately $300 -$500 per event, plan for 10 -12 events)
use existing
Sprayer replacement fund (replacement in 6 yrs = $16,600)
$2,800
Sprayer and trailer license, calibration, maintenance, and fuel
$1,000
TOTAL
$41,925
Total fixed costs (UNT programs and BTI purchase)
$35,125
Total variable / contingent costs (spraying 10 -12 large events)
6,800
Staff suggestions
• Maintain UNT surveillance agreement
• Continue BTI applications at current levels
• Continue RAMP program
• Maintain MSRP in current form
• Secure additional funding needs through
contingency, remaining funds used for
subsequent years
• Consider mosquito program for supplemental
budget.
Options
1. No further action
2. Direct staff to proceed with implementing
suggestions
3. Table for future consideration
• Staff recommended Option 2.
Discussion
EXHIBIT 2
Mosquito Surveillance and Response Plan
City of Denton, Texas
pupa
female
x v a,
'X
a�
eggs
2014 FINAL DRAFT
prepared by Kenneth E. Banks, Ph.D.
Department of Environmental Services and Sustainability
City of Denton
TABLE OF CONTENTS:
1.0 Introduction ........................................... ...............................
1
2.0 Objectives ............................................... ...............................
2
3.0 West Nile Vines Concerns ........................... ...............................
2
4.0 The Role of Residents .................................. ...............................
4
5.0 Denton's Plan for Mosquito Surveillance .......... ...............................
5
5.1 Adult mosquito collections .......... ...............................
6
6.0 Mosquito Control Strategies .............................. ...............................
6
6.1 Larviciding vs. adulticiding ........ ...............................
8
6.2 Rationale for different treatment methods .......................
9
6.3 Integrated Pest Management ......... ...............................
9
7.0 Denton's Plan for Mosquito Control ................. ...............................
10
7.1 Adulticidmg .......................................... ...............................
10
7.1.1 Triggers for adulticiding ........... ...............................
10
7.1.2 When to use adulticides ............ ...............................
11
7.1.3 Where to use adulticides ........... ...............................
11
7.1.4 Human Population density considerations ................
11
7.1.5 Mosquito population considerations .........................
12
7.1.6 Local perspectives on spraying .. ...............................
12
7.1.7 Denton's plan for mosquito adulticiding operations .
12
7.2 Plan for Public Education Concerning Mosquitoes ..............
14
7.3 City of Denton Response Plan ............... ...............................
14
7.3.1 Risk Level 1 -Normal Response ..............................
15
73.2 Risk Level 2 - Enhanced Response ...........................
16
7.3.3 Risk Level 3 - Public Health Concern .......................
17
73.4 Risk Level 4 - Public Health Warning ......................
18
73.5 Risk Level 5 - Public Health Alert .........................
19
References.................................................................. ...............................
21
1.0 INTRODUCTION
Mosquitoes are insects that belong to the order Diptera, or Tree Flies. Female
mosquitoes have modified mouthparts that form a long piercing - sucking proboscis, while
male mosquitoes have mouthparts that are incapable of piercing skin. There are over
2,500 different species of mosquitoes that have been identified throughout the world,
with approximately 150 species occurring in the United States. The Texas Department of
Health estimates that there are approximately 82 -84 mosquito species in the State of
Texas, although only about 12 of these mosquito species have been implicated in the
transmission of serious diseases.
Mosquitoes typically need still, stagnant water that is isolated from fish or other small
predators to complete their metamorphosis from egg to adult. Larval habitats can range
from marshes, freshwater wetlands, and tree holes to human -made strictures like
catchments, drains, gutters, and discarded tires. Not all species feed on humans and
other mammals, and many species feed mostly on birds, amphibians, or reptiles. Only a
small percentage of the known mosquito species are considered to be diseases vectors.
Although only a small percentage of mosquito species are capable of transmitting
diseases, mosquitoes are still considered to be a very important vector for disease
transmission. Within the United States, the occurrences of mosquito -borne illnesses
have been relatively rare in recent years. However, epidemics of mosquito -borne
diseases were once common in the United States. Outbreaks of Yellow Fever have been
recorded as far north as Philadelphia during the Colonial Period, and Dengue fever was
prevalent along the Gulf Coast until the mid- 1940s. Atone time, malaria was well
established in the continental United States, especially in the south. Other mosquito -
borne illnesses like LaCrosse, St. Louis, and Eastern Equine Encephalitis are still threats
in certain areas of the country. Although many of these historical mosquito -borne
diseases have been eliminated or at least controlled, the introduction and subsequent
rapid spread of West Nile Vines within the United States is a topic of current concern.
Mosquitoes may be controlled through a variety of different physical, chemical, and
biological methods. Physical methods usually involve source reduction, which is simply
the physical removal of mosquito breeding habitats. Biological measures mainly center
on the use of bacteria that kill mosquito larvae or the use of natural mosquito predators.
Chemical treatment typically involves the application of pesticides to attempt to control
larva or adult mosquito populations.
Mosquito control pesticides are applied by various means, depending on the type and size
of the area being treated. No matter how pesticides are applied, however, pesticides
have the potential to impact non - target species, including humans. Depending on the
pesticides used, potential impacts may include acute or chronic toxicity, reproductive and
/ or developmental effects, and indirect effects through the food chain. The tests
required for pesticides registration also may not address non - target impacts.
Information regarding the effects of inert ingredients in pesticide formulations, food
chain effects, multi- generational effects, and the interaction of specific pesticides with
other chemicals in the environment may also be lacking. It is therefore important to
realize that there are risks associated with the use of pesticides just as there are risks
associated with the potential for human or animal infection by a mosquito -borne illness.
The purpose of this response plan is to provide a systematic way to consider and balance
the risks associated with mosquito control measures.
2.0 Objectives
The City of Denton Mosquito Surveillance and Response Plan was developed to meet
several objectives. Specifically, the Plan:
• Provides guidelines and information on mosquito populations, prevalence of
diseases, and control strategies;
• Provides a systematic approach for utilizing mosquito sampling and human
disease data to establish Risk Levels;
• Establishes actions that will be undertaken for each Risk Level;
• Provides municipal staff and elected officials with a decision - support system;
• Outlines the roles and responsibilities of municipal staff and elected officials.
3.0 West Nile Virus (WNV) Concerns
West Nile Vines was first recorded in North American during August 1999 shortly
following the Center for Disease Control and Prevention (CDC) and the New York City
Department of Health responses to an unusual outbreak of encephalitis in northern
Queens, New York. The cause of the observed illnesses was determined to be West Nile
virus. During 1999, approximately sixty people were diagnosed with West Nile virus
and seven elderly residents died from the infection. During the summer of 2000, WNV
activity was detected again in New York City and appeared to be spreading. Fourteen
people in the City of New York were diagnosed with acute WNV infection, six were
identified in New Jersey, and I was reported from Connecticut. Outside of New York,
WNV was detected in 12 states and in the District of Columbia. During 2001, the virus
appeared again in New York City, causing seven cases that required hospitalization. In
2001, a total of 66 human cases with nine fatalities were reported throughout the nation,
mostly spread throughout the eastern United States. During 2002, there were 4,156
laboratory- positive human cases and 284 deaths. The number of cases increased
dramatically in 2003 as the disease spread westward, with 9,862 cases and 264 deaths.
After 2003, annual national case counts have ranged from a low of 712 during 2011 to a
high of 5,674 in 2012. In 2012, the highest incident rates in the nation were observed in
the North Texas region, including Denton County.
The relatively rapid spread of West Nile virus and the increase in disease incidence
indicates that WNV is permanently established in the United States. It is likely that the
virus survives the winter either within birds that remain in the area or within mosquitoes
that survive the winter. When spring returns, the virus recrudesces within the birds and is
readily passed to early season mosquitoes. As mosquito populations increase,
mosquitoes begin to feed more frequently on birds, causing an increasing number of birds
2
and mosquitoes that are infected. If environmental conditions are favorable for
transmission, the virus will amplify to a theoretical point of spillover. At spillover, the
virus can bridge out of the bird - mosquito cycle through mosquitoes that feed on birds,
humans, and other animals. At the point of spillover, transmission to humans becomes
more likely. Currently, mosquito control is the only practical method of protecting the
human population from WNV inflection. There are no known specific treatments or
cures for the disease caused by this virus, and vaccines are currently not available for
public use. The virus also kills a variety of native and non - native birds, and may have
impacts on other wildlife.
Weather plays a major role in the prevalence of WNV, and the relatively warm winter
and spring experienced in North Texas during 2011 to 2012 may have been a significant
factor in the prevalence of the disease during the 2012 mosquito season. Understanding
the types of mosquitoes in the area that transmit the disease is also a crucial consideration
for directing control responses and public education activities. Since not all mosquitoes
carry the virus, enacting mosquito control efforts that attempt to non - selectively reduce
all mosquito populations will not necessarily reduce the risk of WNV. In fact, based on
10 years of mosquito monitoring and disease analyses in the City of Denton, there
appears to be only one mosquito that serves as a vector for this disease. Approximately
99 percent of the WNV infected mosquitoes captured in Denton's monitoring program
over the last 10 years have been Culex quinquefasciatus, commonly known as the
southern house mosquito. The control efforts enacted by the City are therefore focused
on this one particular type of mosquito.
The past experience of numerous mosquito control districts suggests that a mosquito
control program should be based on the principals of Integrated Pest Management (IPM).
The principals of IPM are:
• knowledge of mosquito biology and the epidemiology of the mosquito -borne
diseases;
• surveillance and monitoring efforts for the detection and status assessment of
mosquito populations and / or mosquito -borne diseases;
• a multifaceted prevention and control program comprised of a system of control
tactics which are compatible with each other and which are proven effective;
• continued program evaluations and updates to ensure that the best methods are
being used to meet the prevention and control objectives of the program; and
• continual education of the public to create awareness, understanding, and
support.
These general guidelines have been used to develop the threshold -level responses of this
surveillance and response plan.
4.0 The Role of Residents
Residents can play an important role in reducing the number of adult mosquitoes by
eliminating standing water that may support the development of mosquito larva and pupa.
For example, residents can properly dispose of discarded tires, cans, buckets, maintain
pools correctly, unclog blocked gutters and drains, dump water from bird baths and pet
dishes at least every 2 -3 days, ensure that air conditioning condensate is not pooling for
several days, control irrigation so that standing water is not produced, irrigate so that
runoff is not produced, and perform similar activities around homes and businesses.
Water that cannot be eliminated should be treated with a biological mosquito larvicide
such as Bacillus thuringiensis israelensis (Bti) in accordance with manufacturer's
recommendations.
Residents should be aware that Culex quinquefasciatus, the target mosquito for control,
tends to prefer to lay its eggs in "artificial" sources of water such as those listed above, as
opposed to laying eggs in wetland areas, streams, and ponds. Generally, this mosquito
cannot fly long distances, so emerging adult mosquitoes often remain near the habitat
they lived in as larva and pupa. Adults will rest during the daytime in vegetation,
particularly in areas where humidity is high. Irrigated urban and suburban landscapes
can offer excellent habitat, especially if there is standing water present. Underground
storm drains that receive small amounts of runoff from irrigation are also good habitat for
these mosquitoes. As a result, Culex quinquefasciatus tends to become more associated
with urban and suburban areas during the summer months. Often these same areas will
also have birth baths, bird feeders, trees, and other vegetation that serve to attract birds,
especially during the drier times of the year when food and water become scarce. As a
result, the opportunities for WNV disease amplification in urban and suburban areas can
become more pronounced during summer months. The role of residents and business
owners in controlling larval habitat is therefore a crucial component of reducing local
WNV risk.
5.0 Mosquito Surveillance
The risk of mosquito -borne diseases depends on the size of mosquito populations and the
incidence rate of disease, as well as the likelihood of the mosquito population changing in
response to climate factors. Although mosquito abundance can be estimated through
collection of either immature or adult mosquitoes, adult mosquito abundance is a key
factor contributing to the risk of virus transmission. For this reason, the City of Denton
monitoring program primarily focuses on collecting adult mosquito populations for
targeting control measures and gauging the potential for disease outbreak. The current
mosquito surveillance program is a partnership between the City of Denton and the
University of North Texas. This surveillance program collects adult mosquitoes through
the use of both CDC light traps and gravid traps. Captured mosquitoes are sent to the
Texas Department of State Health Services for testing. Each sample (sometime referred
to as a "pool ") consists of female mosquitoes that are collected at a specific collection
site, in one of the two types of trap. The information obtained from these surveillance
4
efforts is used to map mosquito populations, provide public information, and to determine
the incidence of WNV or other arbovirus.
The mosquito surveillance program allows analysts to map potential mosquito breeding
grounds and areas of persistent disease. Using this information, more targeted efforts
towards habitat disruption, source reduction, larviciding operations, and other control
mechanisms are possible. An effective, broadly applied surveillance program can allow
analysts to detect the presence of WNV of other mosquito -borne viruses during the
amplification phase. If targeted mosquito controls are implemented at the amplification
stage, the likelihood of bridging can be minimized, thus reducing the risk of human
transmission. Depending on weather patterns and monitoring results, trapping can be
expanded or contracted and the trapping season may be lengthened or shortened. If
control measures are applied, trapping data may also be of some use for evaluating the
effectiveness of control measures.
The overall goal of the mosquito surveillance program is to use data on mosquito
populations and mosquito virus infections rates to:
• assess the threat of human disease;
• determine the geographical areas of highest risk;
• determine the need for intervention events, and the timing of these events;
• identify larval habitats that are in need of targeted control;
• monitor the effectiveness of control measures; and
• develop a better understanding of transmission cycles and potential vector
species.
Adult surveillance methods should:
Use both fixed and flexible trap locations if possible
• Fixed positions allow for the development of a database so year to year
comparisons are possible;
• Flexible sites allow for responses to epidemiological and natural events.
Use more than one trapping method (CDC light traps, gravid traps, etc...)
o Testing data collected in the City of Denton's monitoring program
suggests that if resource limitations require a choice between CDC light
traps or gravid traps, gravid traps are preferred. These traps have been
more effective in collecting Culex quinquefasciatus and more effective
for establishing the prevalence of WNV.
Account for different influencing factors, including:
• Habitat size and diversity;
• Resource availability;
• Proximity to human population centers and / or recreational areas; and
• Flight ranges of target mosquito vector(s).
Advantages of using adult mosquito surveys include:
• The ability to provide early evidence of viral activity in an area;
• Helpful for determining if viral activity is local and / or restricted to a few areas;
• Providing information on potential mosquito vector species
• Providing estimates of vector species abundance and temporal prevalence;
• Providing information on virus infection rates for different mosquito species;
• Providing information on potential risks to humans and animals;
• Providing baseline data that can be used to guide emergency controls.
Disadvantages of using adult mosquito surveys include:
• The amount of labor required, and associated expenses;
• The need for substantial expertise to ensure proper collection and handling of
mosquitoes;
• The delays associated with receiving mosquito arbovirus screening results;
• The fact that collectors may be at risk from mosquito bites (although using
personal protection methods can minimize risks).
5.1 Adult mosquito collection
The adult mosquito surveys implemented by the City of Denton in conjunction with the
University of North Texas are designed to determine the relative abundance of various
species present during the sampling period as well as the incidence of arthropod -borne
virus /diseases within the captured specimens. Using this information, City of Denton
personnel determines the need for various control measures, and can conduct more
effective searches for larval breeding places, assess the extent of the problem, and
potentially gauge the effectiveness of control measures. Reports concerning the
incidence rates of arthropod -borne virus /diseases and the relative risks to citizens are also
produced. Currently, collections are made using both CDC light traps and gravid traps
deployed simultaneously.
6.0 Mosquito Control Strategies
Human activities can greatly affect the ecology of mosquito populations. Large
concentrations of people or animals, for example, can increase exposure rates and the
probability of disease outbreak. The use of irrigation, development of drainage networks,
elimination of mosquito predators, prevalence of improperly maintained birdbaths and
other water holding containers can increase the numbers of certain types of mosquitoes.
6
Expanding international trade and travel has increased the chance of introducing new
mosquito species into our areas, as has happened with the Asian tiger mosquito (Aedes
albopictus).
Mosquito control strategies have changed dramatically over the last few decades. Diesel
oil, inorganic poisons, and source reduction using ditching operations were the basic tools
of early mosquito control programs. Chlorinated hydrocarbons, organophosphates,
pyrethroids, monomolecular oils, bacteria, and natural predators are more recent
additions to mosquito control efforts. With the growth of ecological consciousness and
environmental science, people began to realize the environmental damage that
accompanied the use of broad - spectrum chemical control agents, particularly those that
did not readily break down in nature. Concerns were also raised because many mosquito
populations also appeared to develop resistance to the more commonly utilized chemical
control agents.
Over the past few years, major advances have been made in the areas of biological
mosquito control. Biological control strategies may include using natural predators like
Gambusia affinis (Mosquito fish), fungi, protozoans, round worms, flat worms, and
bacterial agents such as Bacillus thuringiensis israelensis (Bti). Each biological control
agent has certain benefits and restrictions. In order to use a biological control agent
successfully, the applicator must have a basic knowledge of biology associated with the
control agent. Some biological control mechanisms, for example, are limited by salinity,
temperature, or organic pollution and some mosquito species are much more susceptible
to specific types of biological control agents. All of these factors must be considered
when choosing and applying biological control agents.
The perfect pesticide is one that is easily applied, reasonably inexpensive, not toxic to
non - target organisms, and that eliminates the pest quickly before it becomes a threat.
Although no single pesticide can combine all of these factors, certain types of Bacillus
bacteria have been developed into pesticides that are very close to the perfect pesticide
model. Bacillus thuringiensis israelensis (Bti), for example, is a naturally occurring soil
bacteria that produces a poison capable of killing mosquito larvae. Bti is considered ideal
for mosquito management because of its specificity for mosquito larvae and because of
the minimal to no toxicity to non - target organisms. These bacteria form asexual
reproductive cells, called endospores, which enable them to survive in adverse
conditions. The endospores of Bti also contain crystals of an insecticidal protein toxin
called delta endotoxin. Once ingested by a mosquito, the alkaline conditions of the
stomach dissolve the crystal and release the delta - endotoxin. The toxin has an affinity for
the stomach wall lining causing the cells to first swell then rupture. When enough
stomach cells burst, the mosquito larvae is unable to effectively digest food. Once
affected, larvae stop eating and rapidly die. Currently, Bti is commercially available in
powder, liquid, granular, capsule, and "briquette" formulations.
Agencies applying pesticides directly to waters of the United States, or where deposition
may enter waters of the United States, are required to obtain a National Pollutant
Discharge Elimination System (NPDES) permit from the Texas Commission on
7
Environmental Quality (TCEQ). This permit is titled "General Permit to Authorize Point
Source Discharge of Biological Pesticides and Chemical Pesticides That Leave a Residue
in Water". Agencies must comply with all applicable provisions of this permit (see
TCEQ General Permit TXG87000).
6.1 Larviciding vs. Adulticiding
In the past, many mosquito control programs have relied heavily upon adult mosquito
controls using chemical agents. In certain areas, routine mosquito spraying has been an
integral component of control strategies. However, even near - continuous exposures to
pesticides may not kill all mosquitoes. Those mosquitoes genetically able to resist higher
pesticide concentrations may survive and pass on this resistance to future generations.
Eventually, the pesticide becomes less effective as resistance increases in the mosquito
populations.
Resistance can be minimized through the "Management by Moderation" approach.
Management by moderation is an attempt to prevent the onset of resistance by:
• using doses that are no lower than the lowest recommended application rate to
avoid genetic selection of resistance genes;
• using less frequent applications;
• using chemicals of short environmental persistence;
• avoiding the use of slow release formulations;
• avoiding using the same class of pesticides to control both adults and immature
stages;
• applying pesticides to only hot spots. Area -wide treatments should only be
considered during imminent public health threats;
• leaving certain generations, populations, or population segments untreated; and
• establishing action thresholds that accentuate control mechanisms other than
chemical control of adult mosquitoes.
Although management by moderation is a viable means of minimizing resistance, there
are other environmental and human health concerns associated with the application of
pesticides for adult mosquito control. Routine mosquito spraying, for example, has the
potential to expose the public to pesticides. Depending upon the pesticide utilized,
effects on humans are possible and may be more likely for people who already suffer
from asthma or other respiratory problems. If proper safety precautions are not
followed, applicator personnel may also be in danger of overexposure. Managers must
therefore decide whether mosquito populations and the related threat of disease
transmission or the chemicals used to control mosquitoes represent the bigger threat to
humans.
All mosquitoes begin their lives in water. Prime breeding sites include discarded tires
left outdoors, poorly maintained bird baths, clogged rain gutters, unused swimming pools
and plastic wading pools, pet dishes, or any other container capable of holding water for
more than a few days. Mosquito breeding can therefore be prevented by either
eliminating the source of water (source reduction) or by killing larvae (larviciding).
Larviciding programs use a combination of source reduction, biological, and possibly
chemical measures to control mosquito larvae before they develop into biting adults. If
properly implemented, this strategy can be the most effective, economical and safest
method for mosquito control because mosquito larvae are minimized, thus reducing the
need for adult mosquito control and subsequently reducing the impacts of control
measures on non - target organisms. Larviciding programs also offer the opportunity to
use biological controls, which minimizes the impacts of the control program on non -
target organisms and lessens the risk of chemical exposures to the public. Using
biological controls also minimizes the chance of pesticide resistance in the mosquito
populations. Experience suggests that the most effective and economical way to reduce
mosquito populations is by larval source reduction through a locally funded abatement
program. The goal of this program should be to monitor mosquito populations and
initiate controls before diseases are transmitted to humans or domestic animals (CDC,
2001).
When larval control is not possible or more immediate control measures are needed, adult
mosquito control may be required to diminish populations of infected mosquitoes and
interrupt viral transmission. Adult mosquito control products may be applied using
ground based equipment, fixed wing aircraft, or helicopters. In all cases, products
should be applied in ultralow volume (ULV) formulations and doses, and should be
comprised of pyrethroids.
6.2 Rationale for different treatment methods
Chemical usage should not be viewed as a long -term control strategy, and should be only
implemented when there are occasional episodes of heavy uncontrolled breeding
concurrent with a high degree of public health risk. This strategy is most appropriate
because prolonged use might lead to the development of resistance in mosquito
populations, thereby limiting overall management options (Tabashnik, 1990). The most
efficient and effective program is one in which mosquito larvae are prevented from
becoming biting adults through the use of biological control agents. The bacterium Bti or
the related bacterium Bacillus sphaericus (Bs.) are considered to be the among the most
environmentally acceptable commercially available biological control agents because of
their relative specificity for mosquitoes and negligible toxicity for vertebrates (Rishikesh
et al., 1983). Larvivorous fish can also be a valuable component of an integrated control
program, either alone or together with chemical control agents (Walton et al., 1990;
Walton and Mulla, 1991; Reed et al., 1995). For these reasons, the City of Denton relies
heavily on source reduction and larviciding for mosquito control.
9
6.3 Integrated Pest Management
Integrated pest management dictates that control efforts should be dependent on threshold
levels. This means simply that a certain defined risk needs to exist before particular
control measures are recommended. Levels of risk are based on knowledge of mosquito
biology, the epidemiology of the mosquito -borne diseases, and monitoring efforts for the
status assessment of mosquitoes and / or mosquito -borne diseases. Risks levels are then
used to design multi- tactic prevention and control program that are comprised of a system
of tactics which are compatible with each other and which are proven for their
effectiveness. Continual program evaluations and updates ensure that the best methods
are being used to meet the prevention and control objectives of the program, and
continued public education is used to create awareness, understanding, and support.
Frequent mosquito population assessments allow analysts to map potential mosquito
breeding grounds and determine overall disease transmission risks. Using this
information, more targeted efforts towards habitat disruption, source reduction,
larviciding operations, and other control mechanisms are possible.
7.0 Denton's Plan for Mosquito Control
The primary objective of mosquito control is to decrease the risk of mosquito -borne
human diseases. This objective should be accomplished by:
• Stressing source reduction as a viable means of control, both by residents and on
municipal properties, including enforcement actions for stagnant water located
on private property;
• Aggressively larviciding where such activities are feasible, practical, and likely
to be effective. This includes providing limited supplies of larvicides to citizens
for use on private property.
• Promoting the use of personal mosquito protection measures, especially for the
elderly and those individuals with compromised immune systems, through
public education and outreach.
• Providing public information so that citizens are informed about the current Risk
Level, areas of the City where WNV has been located, current municipal control
measures, and what can be done by the public to help reduce risks.
• If warranted, implement adult mosquito control measures through targeted ULV
pesticide applications (adulticiding).
7.1 Adulticiding
Adulticiding should and will be considered a supplemental control measure. The
decision to spray shall be based on the conditions listed (in no particular order) below.
7.1.1 Triggers for adulticides: Adulticiding shall be considered only when there is
evidence of WNV activity at a level suggesting a high probability of human infection. In
10
general, finding an isolated WNV- positive mosquito pool does not by itself constitute
evidence of an imminent threat to human health and does not warrant adulticiding.
Physicians and laboratories are required by Title 25 of the Texas Administrative Code
(Pt. 1, Ch. 97, Subch A, §973) to report cases of WNV infection or positive test results in
humans to the State and County Health Departments. Positive human WNV cases are
investigated by Health Department officials. During an investigation, the Health
Department collects demographic and clinical information from the patient and attempts
to determine date of onset, whether the infection was acquired locally or from a region
outside of the patient's residence, and whether the infection may have been acquired by a
non - mosquito route of transmission such as a blood transfusion or organ transplant. To
help aid control measures, the Health Department provides some of this information to
municipal officials within the municipality where the patient resides. Human case
information is used by municipal officials as one of the trigger conditions for the risk
levels outlined in this plan
7.1.2 When to use adulticides: The goal of spraying is to reduce the risk of human
diseases by decreasing the number of target adult mosquitoes as much as possible.
However, today's pesticides tend to only be effective when physically contacting the
mosquito, which is most likely to happen when mosquitoes are actively flying. This
typically will mean that spraying should be conducted between dusk and dawn. Since
the target mosquito Culex quinquefasciatus, is thought to be most active soon after dusk,
spraying should be timed to strike the best balance between impacting the target
mosquito during its most active time and minimizing impacts on non - target organisms.
It is also important to realize that weather conditions, including air temperature, have a
large influence on the effectiveness of adulticides. Spray events should be cancelled and
rescheduled if conditions are not conducive for effective spraying.
7.1.3 Where to use adulticides: The terrain of the proposed spraying area has a major
impact on the pesticide effectiveness. If there is substantial vegetation, dense shrubbery,
trees, or hedges, pesticide applications can be rendered ineffective. The density of
houses and other physical obstructions can also influence the effectiveness of pesticides.
Applications should be made so that the maximum penetration into these types of
obstructions is achieved. In some cases, a mild breeze may be able to help distribute the
pesticide. Application strategies should consider the meteorological conditions at the
time of application, and use these conditions to help improve application effectiveness if
possible.
7.1.4 Human population density considerations: The human population density in an
area where there is evidence of intense epizootic activity should also be considered. If
the area in question is rural and does not contain many people, the cost and potential risk
associated with spraying may not justify its use. If the area in question is densely
populated, adult mosquito control may be more justified as long as adequate
precautionary measures are taken.
11
7.1.5 Mosquito population considerations: Information from mosquito surveillance
can be helpful in determining when to conduct mosquito control and to assess the
effectiveness of control measures. It is also important to know the numbers and species
of the vector populations in specific localities. The best way to obtain this information is
through mosquito trapping efforts. The City of Denton formed a partnership with the
University of North Texas to provide the specially trained staff needed for systematic
mosquito trapping efforts.
While trapping efforts are crucial for assessing mosquito populations and the prevalence
of disease, it is important to realize that surveillance specimens requires some processing
time after collection. In the time between the collection date and the date of test results,
circumstances may have occurred which would alter a decision to spray. For example,
weather conditions may have adversely affected mosquito populations, local mosquito
habitats may have been altered, or larviciding efforts may have reduced the number of
newly emerged adults. All of these occurrences may result in a reduced need to spray,
and should be taken into consideration during control efforts.
Surveillance information should also be evaluated through time to determine the progress
of diseases and the relative risk of disease transmission. Surveillance information may
also be of some use in gauging the effectiveness of control measures, although
establishing control effectiveness is difficult using only surveillance information. In all
cases, the available surveillance information should be evaluated as a part of the decision
making process for enacting adulticidal activities.
7.1.6 Local perspectives on spraying: Different communities have different
perspectives on the benefits and risks associated with adulticiding activities. While these
perspectives are valid and should be considered, individuals are likely to have strong
opinions on either side of the issue. The City of Denton has incorporated a rationale
framework within the mosquito control program that is designed to be protective of both
human health and the environment. The decision to spray, however, is a complex issue
that will likely be faced without complete information. Thus, there will be citizens that
do not believe that the City of Denton has done a good job with regards to reducing
public health and environmental risks, regardless of the decision. The mosquito control
program should therefore remain flexible and should attempt to address citizen
complaints through public education and dialogue.
7.1.7 Denton's plan for mosquito adulticiding operations
Once arbovirus activity is detected and the decision is made to implement mosquito
control using adulticides, the size of the area to treat must be determined. Unfortunately,
there is no simple formula for determining how large of an area to treat, nor is there
adequate information to guide decisions about the degree of vector population
suppression that must be attained, or for how long this suppression must be maintained to
reduce the risk of disease. The CDC (2001) suggests considering the following factors
where deciding the scope of the adulticiding effort:
12
• the general ecology of the area;
• the flight range of vectors that are known or are believed to be of importance in
the area;
• the population density of the vectors;
• the length of time since virus- positive mosquito pools were collected;
• the potential risk to the human population (including the age demographics of the
area) as well as the community perception of the relative risk of pesticides versus
the risk of arbovirus infection; and
• the season of the year - how much time the transmission risk can be expected to
persist until the vectors enter diapause;
It is very likely that some of these factors will be unknown or poorly known, and
practical experience in conducting a mosquito control program is needed to refine control
recommendations. If adulticiding operations are conducted, the following parameters
should be monitored:
• Weather conditions during the application (temperature, wind speed, wind
direction, etc...);
• Flow rate of Ultra -Low Volume applications; and
• Overall amount of pesticide applied.
If the application of adulticides is deemed necessary, the public must be informed. The
following actions / activities will take place prior to adulticide applications:
• Information will be released 24 hours in advance through the media and through
the city of Denton web site. Under certain conditions in Public Park areas,
applications may take place in less than 24 hours notice. For these cases, the
facility will be closed to the public during and a few hours after application.
• Press releases should be prepared and shared with the appropriate media
• CodeRed, the Customer Service automated calling systems, and available forms
of social media should be used to inform citizens of spray events. CodeRed will
make an automated phone call with a message to all individuals that have signed
up for the service. The Customer Service automated calling system will make an
automated phone call with a message to all individuals within an area designed
by the spray map. For both systems, it is possible that some residents outside of
the spray area will receive one of these calls. However, these systems are the
most rapid and accurate means of notifying the public of upcoming spray events.
• If practical, street signs indicating that spraying will occur in the neighborhood
should be placed at major roadways entering and exiting the targeted area.
13
7.2 Plan for Public Education Concerning Mosquitoes
Public education is a key component of a successful mosquito control program. Since
the appearance of the West Nile Vines in the United States, the City of Denton has
produced and aired many public service announcements, given numerous presentations,
and provides information on the City web page concerning this disease. Depending
somewhat on Risk level, the following key information will be conveyed to the public:
• The location of WNV positive mosquito trap locations and current risk level;
• Comprehensive prevention strategies and activities used by the City of Denton to
address the threat of West Nile Vines;
• The public will be advised to eliminate standing water sites by removing all
materials that can hold water for longer than 2 -3 days; and
• The public will be informed about the symptoms of West Nile Vines (headache,
high fever, muscle pain, weakness, and disorientation).
Techniques used to disseminate information may include any or all of the following:
• Televised public service announcements using Denton's local cable channel;
• Radio announcements;
• Brochures for public use placed in municipal buildings;
• Postings describing the current risk level placed in municipal buildings;
• Brochures and / or fact sheets to be distributed to community -based organizations,
community boards, elected officials, schools, nursing homes, libraries, outdoor
activity sites, etc.;
• Presentations to elected officials and / or community groups concerning the
current risk level, mosquito population and disease status, and mosquito control
activities; and
• Press releases describing West Nile virus response activities.
7.3 City of Denton Response Plan
The purpose of this response plan is to:
I. Minimize human illness through public education and targeted vector
control.
2. Provide a semi- quantitative measure of virus transmission risk to humans
that can be used to plan and adjust control activities.
3. Map the density of mosquitoes and the incidence of the virus within the
City of Denton.
4. Identify areas where the incidence of disease is high and provide
appropriate warnings to the citizens of Denton.
5. Identify the key vector species that carry diseases within Denton.
14
The prevention of West Nile virus, as with many diseases, is most efficiently
accomplished by ensuring that prompt, accurate information reaches the public. If the
appropriate information reaches the public in a timely manner, personal protective
measures may be implemented, and control strategies can be enacted efficiently.
The City of Denton will provide continuous information on the city web page concerning
West Nile virus, including a frequently asked questions (FAQs) section, disease
symptoms, personal preventative measures, and sources of additional information. If a
sampled mosquito pool tests positive for arthropod -borne virus /diseases, information
describing the location of the sampling event, the date, and other pertinent information
will be provided.
This response plan is partially based on Texas Department of Health recommendations.
The plan is divided into 5 levels based on the risk of human disease. Each risk level is
described below, along with specific recommended responses. In accordance with the
principals of Integrated Pest Management Control measures are recommended for each
level.
Generally, there are 4 surveillance / observational factors that are evaluated to determine
if the trigger condition has been met for a particular risk level. These factors are:
I. Environmental / climatic conditions (mainly temperature, rainfall, and season)
2. Adult Odex quinquefasciatus abundance
3. Virus infection rates in Culex quinquefasciatus and other mosquito vectors
4 Confirmed infections in humans, including epidemiological information.
7.3.1 Risk level 1 - Normal Response
Condition: Probability of human outbreak is none or remote
Trigger: Normal mosquito activity with no evidence of arthropod -borne
virus /disease detected during the past 3 years in vectors, humans, or other
hosts.
Recommended Response:
,Surveillance:
Surveillance is optional. Under the normal response, mosquitoes are considered to be
only a nuisance without significant influences on public health. Complaint calls and
informal surveys of larva and adults will be used to direct mosquito control efforts.
Public Iuf )rmatiou Education:
Publicize methods for mosquito reduction and personal protection prior to the main
season for mosquito activity and outdoor human activities.
15
Control Measures
Use public information to promote source reduction and personal protection. Conduct
standard larviciding approaches using Bacillus thuringiensis israelensis (Bti) .
Rationale:
Larviciding and source reduction / elimination are considered to be the most effective
long -term solutions for mosquito control. The control measures are designed to
accomplish mosquito control by preventing larval mosquitoes from becoming biting
adults.
7.3.2 Risk Level 2 - Enhanced Response
Condition: Probability of human outbreak is low
Trigger: Normal mosquito activity with little or no evidence of arthropod -borne
virus /disease. Enhanced response level is due to recent historical presence
of arthropod -borne virus /disease in vectors, humans, or other hosts within
the vicinity of Denton (approximately 100 miles).
Recommended Response:
,Surveillance:
Surveillance is optional, but strongly encouraged. If possible, conduct routine
surveillance of adult mosquito populations using light traps baited with CO2 and gravid
traps (at minimum). Collected mosquito species should be identified to species level and
mosquito pools should be screened for the presence of arboviruses. If positive tests are
obtained during arthropod -borne virus /disease screening, additional tests should be
performed to determine what type of arbovirus is present.
Public Iuf )rmatiou Education:
Implement all steps for public information established by the Public Communication
Office for this Risk Level. Generally, this will reflect routine public information
concerning methods for mosquito reduction and the importance of personal protection
measures. This information should be disseminated at the beginning of the mosquito
season.
Control Measures
Use public information to promote source reduction and personal protection. Conduct
standard larviciding approaches using Bacillus thuringiensis israelensis (Bti).
Rationale:
Larviciding and source reduction / elimination are considered to be the most effective
long -term solutions for mosquito control. The control measures are designed to
accomplish mosquito control by preventing larval mosquitoes from becoming biting
adults.
16
7.3.3 Risk Level 3 - Public Health Concern
Condition: Probability of human outbreak is low to moderate
Trigger: Arthropod -borne virus /disease isolated from mosquitoes collected during
trapping activities at a single monitoring site.
Recommended Response:
,Surveillance:
Continue to conduct routine surveillance of mosquito populations. If resources allow,
increase surveillance in the area where the positive sample was collected. Use
geographic information systems to plot the location of the positive sample and provide
this information to the public via the City of Denton web page.
Public Iuf )rmatiou Education:
Implement all steps for public information established by the Public Communication
Office for this Risk Level, which includes public notification, press releases, and City of
Denton web page updates with a map of the positive trap location. Notify medical
professionals, veterinarians, and all those registered with the City of Denton's various
public notification options of the presence of the disease.
Control Measures
Use public information to promote source reduction and personal protection. Conduct
enhanced larviciding using Bacillus thuringiensis israelensis (Bti). Increase efforts in
areas where positive mosquito pools were detected. Control measures will be
implemented based on the following IPM criteria: time of year, the extent of previous
mosquito control activities, the current level of mosquito activity, weather conditions, and
surveillance results.
Prepare for ground level spraying activities using ULV applications of pyrethriods.
Ensure adequate funding and personnel are in place for conducting ULV applications.
Rationale:
Larviciding and source reduction / elimination are considered to be the most effective
long -term solution for mosquito control. Increasing these measures in areas where
positive mosquito pools are detected offers an additional degree of risk reduction.
7.3.4 Risk Level 4 - Public Health Warning
Condition: Probability of human outbreak is moderate to high
Trigger: Multiple mosquito pools collected at different times and locations test
positive for arthropod -borne virus /diseases.
Single human case confirmed with laboratory testing
17
Recommended Response:
,Surveillance:
Continue to conduct routine surveillance of mosquito populations. Increase surveillance
in areas where WNV positive samples have been collected if resources are available. Use
geographic information systems to plot the location of positive mosquito samples and
provide this information to the public via the City of Denton web page.
Public lqf )rmation Education:
• Implement all steps for public information established by the Public
Communication Office for this Risk Level, which includes public notification,
press releases, and City of Denton web page updates with a map of the WNV
positive trap location(s).
• Update web page map for all subsequent WNV positive trap locations
• Notify medical professionals, veterinarians, public health officials, and all those
registered with the City of Denton's various public notification options of the
presence of the disease.
Control Measures
Use public information to promote source reduction and personal protection. Intensify
enhanced larviciding efforts using Bti in targeted areas. Consider using Spinosad
products in areas where positive mosquito pools were detected, if applicable. Control
measures will be implemented based on the following IPM criteria: time of year, the
extent of previous mosquito control activities, the current level of mosquito activity,
weather conditions, and surveillance results.
Finalize all actions needed for implementing ground level spraying activities using ULV
applications of pyrethriods
Rationale:
Larviciding and source reduction / elimination are considered to be the most effective
long -term solutions for mosquito control. Increasing these measures in areas where
positive mosquito pools are detected offers an additional degree of risk reduction.
7.3.5 Risk Level 5 - Public Health Alert
Condition: Human outbreak is confirmed
Trigger: Multiple human cases. Cases must be confirmed by laboratory testing.
IN
Recommended Response:
,Surveillance:
Continue to conduct routine surveillance of mosquito populations. If resources allow,
increase surveillance in areas were arthropod -borne virus /disease positive samples were
collected. Use geographic information systems to plot the location of WNV positive
mosquito samples, and provide this information to the public.
Public lqf )rmation Education:
• Implement all steps for public information established by the Public
Communication Office for this Risk Level, which includes public notification,
press releases, and City of Denton web page updates with a map of the WNV
positive trap location(s).
• Update web page map for all subsequent WNV positive trap locations
• Notify medical professionals, veterinarians, public health officials, and all those
registered with the City of Denton's various public notification options of the
presence of the disease.
• Increase public education, emphasizing source reduction, personal protection, and
disease symptoms.
Control Measures:
Use public information to promote source reduction and personal protection. Intensify
larviciding efforts using Bti in targeted areas. Additional larvicides containing IGRs or
pesticides such as Spinosad may be applied at this time. Intensely treat standing water in
City Parks. If the threat to human health is considered imminent, consider targeted
adulticide applications using ground -based Ultra -Low Volume (ULV) equipment. The
decision to spray will be made by a Resolution of the City Council of Denton prior to the
first application, for each mosquito season. Based on information available at the time
of the Council decision, the Resolution may include specific requirements in addition
those outlined in this plan. ULV applications should be implemented in the vicinity
(approximately 1 mile) of areas where positive human cases were detected. When ULV
applications are initiated, notification will be provided to the public as outlined in Section
7.1.
During 2012, the City of Denton utilized Duet, a synthetic pyrethroid product with an
additional chemical designed to induce "benign agitation" of mosquitoes. The purpose
of benign agitation is to increase the likelihood of mosquitoes flying during the
application, which increases application effectiveness. The Duet product is also mineral
oil based, versus water based, which likely increases the compound's effectiveness in the
higher air temperatures typical during summer applications. Mineral oil based
compounds may also be less likely to affect non - target organisms in aquatic
environments because of the lack of solubility of the oil based compound in water.
Control measures will be implemented based on the following IPM criteria: time of year,
the extent of previous mosquito control activities, the current level of mosquito activity,
19
weather conditions, the species of mosquitoes that test positive for disease, the number of
local mosquito pools which test positively for disease, the likely time until a killing frost,
the density of roads or other access to mosquito breeding grounds, and the density of
human populations. Epidemiological data associated with reported human cases of
WNV will also be considered. In general, if an area has been sprayed, that area will not
be sprayed again in response to an additional human case unless the date of onset of the
new case indicates exposure occurred after the previous spraying event. Areas will also
not be sprayed in response to a reported human case if epidemiological information
clearly indicates that exposure did not occur in the City of Denton. If public health
emergencies are declared at the county or state level, the recommended responses
associated with the declaration will take precedence over the control plan of the City of
Denton.
Rationale:
Larviciding and source reduction /elimination are considered to be the most effective
long -term solutions for mosquito control. Increasing these measures in areas where
positive mosquito pools are detected offers an additional degree of risk reduction.
However, at this Risk Level, applications of adulticides may be needed to rapidly reduce
mosquito populations and halt disease transmission. The objective is to kill a high enough
proportion of older adult mosquitoes to break the disease transmission cycle. If adult
mosquito controls are implemented, the approaches for adulticiding outlined in this plan
are effective and are designed to minimize adverse effects to the environment and non -
target organisms.
20
References:
Center for disease control (CDC). 2001. Epidemic/ Epizootic West Nile Vines in the
United States: Revised Guidelines for Surveillance, Prevention, and Control.
Proceedings from a Workshop Held in Charlotte, North Carolina. January 31-
February 4, 2001.
Reed, S.C., Cites, R.W. and E.J. Middlebrooks. 1995. Natural systems for waste
management and treatment. McGraw -Hill, New York, USA.
Rishikesh, N., Burgess, H.D., and Valdekar, M. 1983. Operational use of Bacillus
thuringiensis serotype H -14 and environmental safety. WHO /VBC/83.871,
World Health Organization, Geneva.
Tabashnik, B.E. 1990. Modeling and evaluation of resistance management tactics. In
Roush, R.T., Tabashnik, B.E. (Eds.), Pesticide Resistance in Arthropods.
Chapman and Hall, New York, USA.
Walton, W.E., Mulla, M.S., Wargo, M.J., and S.L. Durso. 1990. Efficacy of a microbial
insecticide and larvivorous fish against Culex tarsalis in duck club ponds in
southern California. Proceedings of the California Mosquito T'ector Control
Association 58:148 -156.
Walton, W.E. and M.S. Mulla, 1991. Integrated control of Culex tarsalis larvae using
Bacillus sphaericus and Gambusia affinis: effects on mosquitoes and non - target
organisms in field mesocosms. Bulletin of the ,Society for T'ector Ecology 16:203-
221.
21