West Nile Virus in Stanislaus County

2005 Summary & 2006 Strategic Plan

Acknowledgements This report is a collective effort made possible by the Stanislaus County West Nile Virus Taskforce. Taskforce members include individuals from the following organizations: Agricultural Commissioner Animal Services Area Agency on Aging/Veterans Services California Department of Food and Agriculture, Animal Health Branch California Department of Health Services, Vector-Borne Disease Section, Northern Region Delta Blood Bank East Side Mosquito Abatement District Environmental Resources Health Services Agency Office of Emergency Services Stanislaus Wildlife Care Center Strategic Business Technology Turlock Mosquito Abatement District U.S. Fish and Wildlife Service

Table of Contents

Executive Summary

1

Epidemiology of Human Cases

3

Equine (Horse) Cases

5

GIS Project (Maps)

7

Exhibit A – Dead Birds

8

Exhibit B – Positive Mosquito Pools

9

Exhibit C – Equine Cases

10

Exhibit D – Human Cases

11

Appendix A Turlock Mosquito Abatement District (2005 Report)

Appendix B Eastside Mosquito Abatement District (Report 2005)

EXECUTIVE SUMMARY Human Infections During 2005, 92 human infections with West Nile Virus (WNV) were reported within Stanislaus County. As such, Stanislaus County had the third largest number of cases within California, behind Sacramento (177) and Riverside (104) counties. The first human case had the onset of symptoms in early July and the last case in October. The human outbreak peaked with onset of symptoms during the first week of August. There was one human death, a 63-year-old male. The cases within county had an age range from 2 ½ years to 95 years with a mean age of 52 years old. Males and females were equally affected. There is no vaccine for humans. Prevention focuses on mosquito abatement and personal protection.

Equine (Horse) Infections The first equine case in Stanislaus County was reported in the first week of July, and the last case in September. A total of 42 equine infections were reported with 18 deaths. A vaccine for horses has been widely used for the past two years. It can be assumed that a large proportion of horses in the county were properly vaccinated.

Mosquito Abatement The East Side Mosquito Abatement District (EMAD) and Turlock MAD (TMAD) surveillance for West Nile virus consisted of the following: • • • • • •

Control technicians sampling known mosquito breeding environments. Responding to service request from the public. Placement of 8 sentinel Chicken flocks. Placement of New Jersey Light traps in all communities and in multiple rural locations to monitor adult mosquito occurrence. Collection of adult mosquitoes using baited traps for population density determination and testing for WNV. Collecting and testing dead birds for WNV infections.

These activities resulted in the Districts treating 258,178 acres to protect the public from West Nile virus. We found that all lands in Stanislaus County east of the San Joaquin River had the greatest WNV activity in 2005. The Districts found that the house mosquito, Culex pipiens, the most abundant species of mosquito found in the county was the primary mosquito responsible for WNV infections in both people and animals (birds and horses). The house mosquito is found West Nile Virus in Stanislaus County - 2005 Summary & 2006 Forecast Page 1

in a variety of habitats in rural settings such as backyard sources and in storm drainage systems. This kind of mosquito moves in around houses and will frequently enter dwellings. WNV was present even when mosquito populations were at extremely low levels. Given these considerations the Districts have concluded that it is impossible to prevent WNV human or animal infections, but that Districts can lower the public risk of getting WNV. Additionally, in communicating with the public we found public misperception that use of insect repellents was unnecessary because they did not perceive there were enough mosquitoes present to worry about getting WNV.

Forecast and Strategic Plan for 2006 It is probable that Stanislaus County will experience a second year of significant WNV activity. This is anticipated because: a. b. c.

There was widespread infection documented during 2005. A mild winter with opportunities for infected mosquitoes to hibernate. An unusually wet spring with regional flooding. This slowed the schedule of early spraying for mosquito larvae and provided environmental conditions for breeding.

The West Nile Virus Taskforce will continue inter-agency collaboration to maximize prevention and abatement activities. New strategies include: 1. 2. 3. 4. 5.

Broadcast of a dramatic public service announcement regarding the serious health risk. Launch of the STANEMERGENCY.COM website to increase public access to information. Posting of GIS maps on local websites identifying zip code identifications of infected dead bird and positive mosquito samples. Distribution of checklists to county residents to assist with locating sources of mosquito breeding on their property. Assessing fines to residents who do not clean up hazardous sources of mosquito breeding.

In preparing for 2006, the Abatement Districts plan to increase collections of adult mosquitoes to detect WNV and apply control measures to lower the public’s risk of getting WNV. Additional spray equipment has been upgraded to improve on spray efficiency. The Abatement District Managers anticipate that WNV activity will continue in those locations where it was found last year, but that the activity may be slightly diminished. The Abatement District Managers are concerned that the Westside of Stanislaus County may see greater WNV activity than last year. In preparing for WNV in 2006, the Districts plan to intensify surveillance efforts county-wide to isolate virus activity and to suppress those populations. Additionally, the use of digital aerial photography is planned for the communities in the Westside in 2006 to isolate mosquito breeding found in backyards, where access is limited.

West Nile Virus in Stanislaus County - 2005 Summary & 2006 Forecast Page 2

EPIDEMIOLOGY OF HUMAN CASES During 2005 92 human infections with West Nile Virus were reported within Stanislaus County. As such, Stanislaus County had the third largest number of cases within California, behind Sacramento (177) and Riverside (104) counties. However, our case rate per 100,000 residents was 20.6, which was higher than either Sacramento (14.5) or Riverside (6.7). The cases within county had an age range from 2 ½ years to 95 years with a mean age of 52Y. Males (47 cases) and females (45 cases) were approximately equal in proportion. (Race was not available on all cases so that we do not have that percentage breakdown.) The first human case had the onset of symptoms in early July and the last case in October. The human outbreak peaked with onset of symptoms during the first week of August. There was one human death, a 63-year-old male.

20 19 18 17 16 15 14

Confirmed Cases

WN Neuroinvasive 13 12

WN Fever

11

No Symptoms

10

Unknown

9 8 7 6 5 4 3 2 1 0

5 00

05

05

05

West Nile Virus in Stanislaus County - 2005 Summary & 2006 Forecast Page 3

/2 /10 10

20 /3/ 10

0 6/2 9/2

0 9/2 9/1

05

05

05

05 20

0 2/2 9/1

/ 9/5

0 9/2 8/2

0 2/2 8/2

05

05 20

05

05

05 20

0 5/2 8/1

/ 8/8

/ 8/1

0 5/2 7/2

0 8/2 7/1

05

05 20

0 1/2 7/1

/ 7/4

Date of Onset by Week

The cases can be divided into three groups: 1. No symptoms (predominantly blood donors) 2. West Nile Fever 3. Neuroinvasive West Nile Virus (encephalitis)

7% 71% 22%

Analysis and Comments We strongly suspect that this is an under estimation of those infected with WNV in our county. It is likely that number of blood donors is accurate, as well as those presenting with neuroinvasive disease since those individuals were quite symptomatic and required hospitalization. The area where there is a probable under-estimation is the group with West Nile fever, which often presents as a flu-like illness and therefore may not be diagnosed as West Nile Virus infection. This illness can be prolonged with symptoms as long as six weeks. Another significant issue in detection and reporting of WNV infection is the length of time between onset of symptoms and presentation for health care and subsequent test results. This can range from days for blood donors who are screened prior to onset of symptoms to six to eight weeks for those who were hospitalized or present to their personal Health Care Provider with a prolonged less severe illness. Case data regarding the geographical location of individual victims has been obtained and remain confidential. However, zip code rates for the entire cohort are displayed in Exhibit ‘D’ (page 11) and suggest that a predominance of cases occurred within urban areas. Most zip codes within the county had human cases. The predominance of cases in urban areas of Stanislaus County may be the consequence of higher infection rates in household mosquitoes (Culex pipiens) as compared to Culex tarsalis which is the species considered to be the primary vector of West Nile Virus in rural settings. Due to its ability to inhabit and replicate in a variety of water quality environments and temperatures the house mosquito is commonly found in backyard water sources. These sources are extremely hard to locate and control in urban settings. Additionally, this type of mosquito prefers to enter homes and tends to accumulate on vegetation surrounding the home. Culex tarsalis, however, requires cleaner water and cooler temperatures and is more common in rural areas, particularly agricultural settings. It may also reflect the higher difficulty of eliminating backyard sources of mosquito breeding as compared with open agricultural areas that are easier to inspect and spray for both larvae and adult mosquitoes.

West Nile Virus in Stanislaus County - 2005 Summary & 2006 Forecast Page 4

EQUINE (HORSE) WNV CASES The first equine case in Stanislaus County was reported in the first week of July, and the last case reported in 2005 was in September (fig 1).

Incidence of Equine WNV Cases in Stanislaus County by Week, 2005 10 9 8 7

5 4 3 2 1

9/ 23 /2 00 5

9/ 16 /2 00 5

9/ 9/ 20 05

9/ 2/ 20 05

8/ 26 /2 00 5

8/ 19 /2 00 5

8/ 12 /2 00 5

8/ 5/ 20 05

7/ 29 /2 00 5

7/ 22 /2 00 5

7/ 15 /2 00 5

7/ 8/ 20 05

0 7/ 1/ 20 05

Incidence

6

Start date of Week

Fig 1. Equine WNV Epidemic curve in Stanislaus County, 2005.

The spatial distribution of cases was not uniform, and occurred most frequently in areas that have the largest horse populations. The proportion of fatal cases, and vaccination status of cases reveal that none of the clinically affected horses were given a complete series of vaccinations, and partial vaccination only protected the horses from death in approx 40 percent of all cases (fig 2). None of the cases in Stanislaus County received a complete series of vaccinations. As the total proportion of horses in the county that developed the disease was very low, it can be assumed that a large proportion of horses in the county were properly vaccinated.

West Nile Virus in Stanislaus County - 2005 Summary & 2006 Forecast Page 5

Fig 2. Incidence of Equine WNV cases in Stanislaus County in 2005 shown by Zip Code. Pie charts depict proportion of cases that were fatal or not, and vaccination status of each case.

Analysis and Comments Although horses make good sentinel animals, it is unfortunate that anyone has to see their horse suffer or die, since this disease can largely be prevented by a good vaccination program. We need to increase awareness in both the equine veterinarian and public populations as to preventative measures, recognition and treatment of this disease. CDFA has available several brochures for distribution to the public which need to be available at all feed stores that cater to equine customers, and to all veterinary practices whose clients may include horse owners. Feed stores that deal in pet birds and poultry are having these materials delivered to them, thanks to the Avian Health Group. Other sites that should be considered for brochure distribution are auction yards, fairs, rodeos, horse shows, and pet stores.

West Nile Virus in Stanislaus County - 2005 Summary & 2006 Forecast Page 6

GIS PROJECT At the height of the outbreak during early August it became apparent that there was a need to examine and attempt to identify linkages between dead bird reports, human infections, positive mosquito pools, and illness in horses. The Strategic Business Technology (SBT unit of the County Information Technology Department assisted with this effort.

West Nile Virus in Stanislaus County - 2005 Summary & 2006 Forecast Page 7

Dead birds (Exhibit ‘A’) This demonstrates that WNV was detected in dead birds with highest frequency in the central and eastern portion of the county. It is noteworthy, however, that the extreme western portion is primarily wilderness with the Diablo Range. Page 8

Positive mosquito pools (Exhibit ‘B’) This demonstrates the high prevalence of mosquito infection in the southern and western part of the county. Mosquito data is unavailable for the eastern portion of the county so it is not possible to correlate with the location of human cases. Page 9

Equine cases (Exhibit ‘C’) This may be the most indicative of the GIS maps in that horses don’t generally move and therefore are more likely to become infected in the location where they are stabled or pastured. This map demonstrates that equine cases occurred most frequently in areas having the largest horse populations and may indicate areas having a higher proportion of unvaccinated or partially vaccinated horses. Page 10

Human cases (Exhibit ‘D’) This demonstrates that while human infection with West Nile Virus was detected throughout most of the county, the predominance of cases occurred in urban areas of the central portion of the county. Page 11

Appendix A Turlock Mosquito Abatement District – 2005 Report

Turlock Mosquito Abatement District Report on West Nile Virus Activities 2005 The Turlock Mosquito Abatement District provides mosquito control for all residents in the communities, including cities of La Grange, Hickman, Montpellier, Denair, Ceres, Keyes, South Modesto, Turlock, Grayson, Westley, Patterson, Crows Landing and Newman. The District has an integrated mosquito control program that is consistent with basic principles enunciated in the following steps: 1. The employment of qualified technical specialists, using proven methods for mosquito control, equipment, and materials correctly applied. 2. A primary mosquito sources reduction program (eliminate mosquito breeding). 3. Surveillance program to assess mosquito populations and the presence of disease carrying mosquitoes. 4. Mosquito control including both a larviciding program and adulticiding program. 5. Public education through media, citizen contact personally or in-group settings. The District uses source reduction as the preferred method of control, and to consistently work toward source elimination in preference to shorter-lived controls such as spraying for mosquitoes. The District followed the California Mosquito-Borne Virus Surveillance & Response Plan developed by the California Department of Health Services. The District relied upon the West Nile Risk Assessment table found in the State’s response plan to determine response levels. As an example on July 15th even though mosquito populations were above normal as a result of the flooding along the San Joaquin River and its’ tributaries the Districts’ assessment indicated that our response level should be emergency planning for WNV. Some 2 weeks later we were at the epidemic level. The District also used the Operational Plan for Emergency Response to Mosquito-Borne Disease Outbreaks that was developed by California Department of Health Services working in cooperation with the Department of Emergency Services. The Stanislaus County West Nile Task Force adopted these plans as a basis for response to WNV in Stanislaus County.

The Turlock Mosquito Abatement District did the following to protect the people of Stanislaus County from West Nile virus. It should be noted that it is impossible to prevent human infections with West Nile virus but it is possible to lower human risk and to provide the public with information about actions they can take to lower their own risk.

Surveillance: • • • •

• •

•

•

Hired one additional full time person in October 2004. Lowered thresholds for controlling mosquitoes beginning in March 2005. Placement of 21 New Jersey Light traps to monitor mosquito populations beginning March 1, 2005. (At least one trap placed in each community and traps in County). Placed Sentinel Chicken flocks in the following 7 locations: near San Joaquin River National Wildlife Refuge south Maze Rd, Grayson, Jennings Road/Westport drain, Denair, Hickman, Crows landing/San Joaquin River, Hills Ferry Rd/River Rd. Began checking chickens for WNV infections starting May 1st and currently continuing. Began trapping for adult mosquitoes using EVS baited traps/gravid traps. Traps placed every other week beginning in May 2005 and continuing through midNovember. EVS baited Traps were placed in 34 locations, district wide, additionally EVS baited traps were placed as virus was detected or mosquito populations exceeded normal levels. Gravid traps were placed in Ceres and Turlock to isolate WNV activity. District purchased rapid testing systems to detect WNV in mosquitoes and dead birds. The District tested all mosquitoes with rapid turn around of 1 day and dead birds were tested within 4 hours of pick-up. Samples were sent to University California Center for Vector-Borne Disease Research for confirmation. In late August 2005, aerial photographs for the Denair/Turlock area were taken to find potential mosquito breeding sources in residential backyards.

Control: • • • • • •

March 2005 District personnel began early inspections and control of all mosquito breeding sources including catch basins found in communities. Thresholds were lowered in anticipation of WNV activity. Hired Flying Service to perform as needs aircraft applications. Purchased 2 additional aerosol units designed to control adult mosquitoes. District sprayed all locations where WNV was detected or adult mosquito populations were above normal levels. Began wide area adulticiding operations based upon surveillance data. District personnel responded to citizen complaints usually with a 24-hour period. District personnel responded to 494 citizen complaints, excluding: dead bird calls, inquiries about WNV.

Public Education: • • •

•

•

The Stanislaus County WNV task force conducted the majority of the public education relating to WNV activity. District personnel informed concerned citizens about WNV. Through the District’s source reduction program and weed control program worked with property owners to prevent mosquito breeding. The District had over 300 dairy/waste water ponds on its’ voluntary weed control program to reduce/eliminate mosquito control providing weed control at owners expense. District sent out spray notification to communities prior to spraying when possible. The balance between giving the public advanced notice for spraying and protecting the public is a delicate one. On occasions the District made the determination that it was best to spray for infected mosquitoes and protect the public than to continue to put the public at risk so that advanced notice could be given. The District along with East Side MAD, San Joaquin County MAD, Merced County Mosquito Abatement District purchased television spots to run the Lindsay Wagoner Public Service Announcement (PSA) to alert the public about WNV and action they could take to lower their risk. The spots ran for the month of August on KXTV with an estimated market reach of 2.4 million viewers.

Outcome for WNV 2005: WNV activity was highest east of the San Joaquin River even though some activity was isolated in the Newman and Patterson area. It appears that the WNV epidemic began around the first of August and continued to express itself through October 2005. The District believes that the Culex pipiens, house mosquito, was the primary vector responsible for the majority of human infections in Stanislaus County. This is based upon the fact that of the 111 mosquito samples testing positive for WNV, 102 were house mosquito samples. The District also found sample sizes as small as four (4) mosquitoes testing positive for WNV. Normally, an individual would not notice any mosquitoes with a trap count as low as 4 mosquitoes. This indicates in communities with low mosquito populations, much lower than normal background levels, there is risk to becoming infected with WNV. The District believes its’ approach to setting traps where WNV activity was found and within one mile of the surrounding areas helped us do a better job at controlling mosquitoes.

Surveillance Information: Year:

2005 2004 2003

WNV Positive Mosquito Samples: 111 3 0

Total Mosquito Samples:

WNV Positive Chickens:

1,349 624 0

65 9 0

WNV Positive Dead Birds: 150 30 0

WNV Positive Equines:

WNV Positive Humans:

18 1 0

16 0 0

Note: 1 human death from West Nile virus.

Mosquito Control Results:

Year:

2005 2004 5-year avg.

Mosquito Larval Control: Number Acres Applications: Treated: 7,538 7,082 7,009

7,923 4,907 6,325

Mosquito Adult Control: Number Acres Applications: treated: 794 403 267

Total Acres Treated: 107,668 115,591 29,698 34,605 15,642 21,967

Note: Not included in mosquito control results are the catch basins treated in all communities through out the District. The District treated 15,102 catch basins in 2005 to control mosquito breeding in storm drain systems. The total catch basins treated would have been higher if the District did not place a slow release material specific for mosquitoes that are effective for 120 days.

Preparing for 2006: • • • • •

•

District has contacted property owners recommending actions they can take to reduce mosquito breeding on their property including warning notices as warranted. Upgrading 3-additional aerosol units to increase our ability to conduct wide-area adulticiding. Meeting with governmental agencies to better control mosquitoes found on government lands. Updating mapping system and updating district database using GPS locations for know mosquito-breeding locations. Working through Stanislaus West Nile Task Force to develop public service announcements that engage the public to take action to protect them against WNV. As well as working with county Strategic Business Technology Department to develop a GIS mapping system for surveillance and control efforts. The District has analyzed the information gained about WNV activity and is making plans to make adjustments to our operational plans for 2006 that will make us more efficient. Our plan is to place baited traps on locations where virus activity was high in 2005 well before anticipated WNV activity to gauge adult mosquito control and to react to increased mosquito control populations by aggressively spraying larval as well as adult stages in those areas.

The District anticipates that WNV will continue to be active in Stanislaus County and expects that more activity will occur on the West side of the county in 2006. Our most active locations on the east side of the San Joaquin will have virus activity but not to the extent that was present in 2005. The District received $162,088 grant from the State of California in FY 2005-2006 to help control mosquitoes carrying West Nile virus. The District anticipates that its’ expenses will exceed its’ revenues in FY 20062007. The District is hopeful that additional funding will be made available in FY 20062007.

Appendix B Eastside Mosquito Abatement District – 2005 Report

East Side Mosquito Abatement District 2005 West Nile Virus Activities The East Side Mosquito Abatement District provides mosquito control for all of Stanislaus County, north of the Tuolumne River including the communities of Valley Home, Oakdale, Knights Ferry, Waterford, Riverbank, Empire, Salida, and Modesto. The District was formed in 1939 and consists of 520 square miles and has approximately 379,978 residents. The District performs daily mosquito control activities that are carried out in the following manners. 1. Surveillance, including sentinel chicken flocks, light traps, and baited light traps. 2. Source reduction, which is the preferred means of mosquito control. 3. Larvaciding, which eliminates mosquitoes before they impact the public. 4. Adulticiding, which is required when an abundance of mosquitoes are found in an area. 5. Public education through media, citizen contact personally or in-group settings. The California Department of Health Services developed a Mosquito-Borne Virus Surveillance & Response Plan that the District followed during the 2004 and 2005. The West Nile Risk Assessment contained within the plan determined the District’s response. Because Turlock and East Side Mosquito Abatement Districts are in close proximity to each other, our response plans were made on a countywide assessment. According to the Risk Assessment, we were at an epidemic level by August 1. The Plan was activated by both Districts as well as the Stanislaus County West Nile Task Force. East Side Mosquito Abatement District started in 2004 to protect the public from West Nile Virus by hiring additional employees, certifying three additional current employees with the California Department of Health Services, calling all seasonal employees back to work one month earlier than usual, and budgeting for more control activities. The Districts in our Region consisting of Merced, Turlock, East Side, and San Joaquin, formed a mutual aid agreement to assist in the event that a District needed additional support. •

•

The District has several New Jersey Light traps that are placed throughout the county in the same locations over many years so there is a comparison of mosquito populations over time. Early in the year the counts were higher than average in traps located near the Tuolumne, and Stanislaus Rivers due to the fluctuating water line from reservoir releases. There were extra man-hours and costs associated with this problem. The District also started in March (one month earlier than normal) eliminating sources and lowering adult mosquito populations.

•

•

• • •

• • •

•

•

Sentinel Chicken flocks are placed in areas that are historically known to have higher adult mosquito counts. These chickens are then bled once every two weeks to test for Virus activity in the area. These chickens are tested from May through the end of the season. As the season progressed, baited light traps were set at locations that birds were testing positive to WNV to try to track where the virus was located in the mosquito population. When positive mosquitoes were found, areas around that point were treated for adults and the areas checked for producing sources. We found that the number of adult mosquitoes required to spread WNV was lower than the number that were considered to be nuisance numbers in the past, requiring us to try to lower numbers more than past years. The District Aircraft was fitted with a spray system that allows large areas to be treated with pesticide delivering a droplet size required by the pesticide label. This droplet is like a fog that drifts into target areas. Catch basins are treated by two truck mounted right hand drive pickups equipped with dispensers that apply a 30-day larval control material. The District treats more than 27,000 catch basins on a monthly basis. Another good surveillance tool used by the District is service requests called in by the public. Often the public informs the District of a potential problem before it is apparent through surveillance. The District takes pride in the fact that most all requests are answered within 24 hours after being received. Even with the added press from other Districts and the local threat, the service requests for the year were only up by 5% over 2004. This is due to the lower numbers of adult mosquitoes this year. This year the District purchased 3 new aerosol cold foggers that incorporate radar controlled dispensing of material insuring proper applications. When possible the public was informed in advance of a large spray activity. In some cases this was a hindrance due to the time lapse between detection of adult mosquitoes, press time and treatment applications. The State confirmed that 57 of the 103 birds collected by the District tested positive for WNV. The most concentrated area of positive birds were found in the 95356, 95350, and 95355 area codes. Although the mosquito populations were low (between 4 and 7 per baited trap night) some WNV activity was detected prompting the large area spraying of most of the city of Modesto. All communities in the District received some large area spray services but did not receive the amount of press that Modesto generated. With the help of the different agencies of the West Nile Task Force, we were able to distribute flyers educating the public on WNV facts in both English and Spanish. During the season District personnel informed citizens about WNV, and steps that could be taken to lower their risk. Also the member Districts within our region, purchased television time to educate the public through PSAs. As mentioned earlier, District staff worked with landowners to reduce the sources from irrigation and back yard sources. We feel that backyard sources are the major contributing factor to mosquito populations in urban areas.

Surveillance Information: Year:

WNV WNV WNV WNV Positive Positive Positive Positive Chickens: Dead Equines: Humans: Birds:

2005

3

57

45

64

Mosquito Control Results: Mosquito Larval Control: Year: Number Acres Applications: Treated: 2005 2004

9,238 6,397

24,735 12,933

Mosquito Adult Control: Acres Total Acres treated: Treated: 117,852 38,816

142,587 51,749

Preparing for 2006: •

•

The District is in the process of renovating the laboratory and installing new equipment to allow for same-day test results. In the past the Department of Health Services, Vector Borne Disease Section, performed all bird and mosquito sample tests for the District. This caused a lag time of from one week to as much as two weeks. Working through Stanislaus West Nile Task Force to develop public service announcements that engage the public to take action to protect them against WNV. As well as working with county Strategic Business Technology Department to develop a GIS mapping system for surveillance and control efforts.

The District anticipates that WNV will continue to be active in Stanislaus County. The District will remain vigilant in its efforts to do what is possible to lower the risk of WNV transmission throughout the district.