Floodwater water mosquitoes (Aedes vexans) are below average due to control efforts and lack of any significant precipitation throughout most of the District. The last significant floodwater mosquito hatch in our area was around June 3 &4^th. Rain on July 9^th, except in some isolated areas, is not expected to dramatically increase floodwater mosquitoes unless more precipitation breaks the ongoing severe dry spell. Most of our control efforts have been directed at Culex stagnant water mosquitoes. Catchbasin, detention/retention & building foundation (Villages are encouraged to report new building constructions to NWMAD) treatments are the predominant production areas. The District is on its second round of catchbasin treatment with the insect growth regulator methoprene. Other stagnant water sites will be treated with the microbial insecticide Bacillus sphaericus. Homeowners are encouraged to remove any stagnating water on their property that may produce these mosquitoes. Typically their numbers start to increase this time of the season despite the lack of rainfall.

ADULT MOSQUITO SPRAYING

Because West Nile virus (WNV) has been found in birds and mosquitoes in our District and Culex mosquito numbers are on the rise it is likely that we will engage our night spraying program either after the rains this week or next week weather permitting. Targeted areas would be Wheeling, Northbrook and Prospect Heights where WNV positive birds or mosquitoes have been found. Additionally spraying will be scheduled in areas of high mosquito trap counts, landing mosquito reports and residential areas near wooded harborage areas.

MOSQUITO VIRUS SURVEILLANCE IN ILLINOIS

NWMAD has tested 110 Culex mosquito pools to date for West Nile Virus and St. Louis encephalitis. Two mosquito pools have tested positive for WNV via the VecTest. One pool was from Northbrook and the other from Wheeling. The Northbrook pool is being retested via PCR by the Illinois Natural History Survey (DNR). Mosquito pools testing positive in the District will be posted in this Newsletter as well as the NWMAD website VECTEST RESULTS.html.

DEAD BIRD SURVIELLANCE INFORMATION:

As of this writing 21 birds have tested positive for WNV in Illinois according to the Illinois Department of Public Health. Birds were collected from Champaign (1), Clark (1), Cook (4),DuPage (4), Edgar (2), Jackson (2), Kane (2) Kankakee (1), Lake (1), Stephenson (1), Vermilion (1), Whiteside (1) counties. Current information about WNV can be found on the state’s website www.idph.state.il.us/envhealth/wnv.htm or by calling 217-782-5830.

Cook County Department of Health is coordinating dead bird collections in our District. Health Departments should contact the WNV Program Manager LaTrice Porter-Thomas (708-492-2035) if they wish to submit dead birds for testing or have any questions regarding surveillance practices. As before, residents of the District should first contact their local Health Department if they find a dead blue jay or crow.

Important: NWMAD will hold birds for testing if requested (resources permitting) providing that the suspected birds are positively identified as crows or blue jays dead less than 48 hours and the local municipality health department has contacted Cook County about the dead bird submission. Note: the state is no longer collecting raptors (i.e. hawks) or birds other than crows & blue jays for testing. Local health departments should refer to the memorandum from Carl W. Langkop, Chief Communicable Disease Section, and Linn Haramis, Program Manager Vector Control/Arbovirus Surveillance (IDPH) for bird submission details.

WEST NILE VIRUS AND THE ELDERLY

Although the risk of being bitten by a WNV infected mosquito is considered small and most people that are infected show few to no symptoms of the virus it’s important to remember that those most likely to be susceptible to the virus are the elderly (50+) and individuals with compromised immune systems. The reason for the susceptibility in this age group is not entirely understood but thought to be due to decreasing immunity as a person ages. Some suggestive evidence to support this theory is that children appear to be less sensitive to WNV because of immunity passed on to them by their mothers. It is therefore very important that the elderly be warned to avoid mosquito bites during peak mosquito activity (esp. around and between dusk and dawn).

WEST NILE VIRUS IN 2002: WHAT NEXT?

It is uncertain what WNV will do in the remainder of the 2002 mosquito season here in northern Illinois. It is very likely that as predicted back in 2001 the virus will continue to spread throughout IL. and the rest of the Midwest. WNV positive birds have been found in 12 counties in IL and in IN, WI, OH and MI. If WNV in the Midwest follows the same progression it did in states on the eastern U.S. we can expect to see an increasing number of dead birds (esp. crows) in the next few weeks. Human & horse cases are more likely to occur in August or September. Additionally, health experts warn that because WNV is from the same family of viruses as St. Louis encephalitis it is possible that the impact of the virus could increase if the weather returns to hot, dry conditions which favor the production of Culex mosquitoes thought to be the primary vectors of WNV.

REDUCING THE RISK OF MOSQUITO BITES:

Avoid outdoor activity if possible from dusk to dawn when the mosquitoes bite the most. If you do go out wear light colored protective clothing and insect repellent (always read label warnings and directions). Make sure mosquitoes do not enter homes through unscreened or broken doors or windows. Residents are encouraged not to create mosquito harborage areas. Make sure tall grassy areas are trimmed and other vegetation is cut back. If plants must be watered do so in the morning so the vegetation and soil has a chance to dry making it less attractive to mosquitoes. Empty any containers holding stagnating water for 5 days or longer like: tire casings, bird baths, flower pots and barrels that may produce mosquitoes. Neglected swimming pools may produce thousands of mosquitoes. Call the District to report stagnant water areas that remain wet for more than 5 days.

Mike Szyska

Director

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