MEDICALLY IMPORTANT MOSQUITOES

Culex mosquito numbers in gravid traps have decreased over the past few weeks but high numbers in some of our eastern and southern traps prompted our recent adulticiding (night spraying) on 07/24/03. Gravid traps primarily collect only Culex mosquitoes, which are important vectors of West Nile Virus. The elimination of Culex mosquitoes is necessary to reduce the amplification of West Nile Virus in the local bird population and, of course, potential spillover of virus to humans. The situation to prevent is high numbers of Culex mosquitoes increasing the risk of these vectors biting a WNV infected bird and then infecting more birds and eventually humans.

NUISANCE MOSQUITOES

Floodwater, nuisance, mosquitoes (Aedes vexans) are slowly starting to increase due to almost weekly rainfalls. Crews have reduced their impact by larviciding all floodwater areas. We have now resumed using Altosid pellets & 150-Day briquettes (insect growth regulator, methoprene) in our larviciding operation. This is necessary because of the residual properties of these formulations and because our seasonal crews will begin departing in a few more weeks.

ADULT MOSQUITO SPRAYING

Adulticiding (Night Spray Operation) was performed on 06/30/03, 07/01/03 and 07/24/03. On 06/30/03 & 07/01/03 the western portion of Northbrook, eastern Wheeling Township, and the Villages of Des Plaines, Niles, Glenview and Park Ridge bordering/near the Des Plaines River were sprayed due to elevated Culex numbers in our surveillance traps. Barrington Township and a portion of northeast of Hanover Township were also sprayed due to high Culex mosquito numbers. On 07/24/03 the western portion of Northbrook was sprayed due to the presence of WNV infected mosquitoes (http://www.nwmadil.com/VECTEST20031.htm ). In addition, the northeast portion of Wheeling Township, the southern portion of Elk Grove Village and the southeast portion of Schaumburg Township were sprayed due to high Culex mosquito numbers.

Our Night Spraying Program helps reduce adult Culex numbers and it is the only practical method of eliminating adult mosquitoes already infected with WNV and capable of transmitting the virus to more birds (amplification) or possibly humans.

WNV RISK TO HUMANS INCREASES DURING JULY AND AUGUST

Culex mosquitoes primarily feed on the blood of birds and don’t normally prefer humans. When numbers of these mosquitoes increase as they typically do into the summer the chances that they may take a human blood meal also increases. In 2002, at this same time, we saw increasing numbers of WNV infected mosquito batches and the start of human infections. Currently, only one mosquito batch in Northbrook has tested positive for WNV in the District. Since that positive batch, and our subsequent adulticiding in that area, four other batches of Culex mosquitoes have been tested from the same trap and all have been negative. Culex numbers are also, presently; lower than in 2002 during this same time. Cooler temperatures in 2003 compared to 2002 has also slowed down mosquito developmental rates. A return back to normal temperatures could quickly reverse this trend.

Homeowners are strongly urged to remove any stagnating water on their property that may produce these mosquitoes. Virtually any water container (i.e. flower pots, garbage cans, pails, bird baths, un-maintained swimming pools, etc) containing organic debris like leaves or grass can produce hundreds of these mosquitoes in about a week’s time during warm temperatures. Homeowners should also avoid watering lawns near open ditches or low areas that may cause water to accumulate in culverts under roadways. Mosquito repellent containing DEET should be worn outdoors in areas of mosquito activity especially around dusk and dawn.

EASTERN EQUINE ENCEPHALITIS- EVANSTON

The Illinois Department of Public Health on July 14^th reported a case of Eastern Equine encephalomyelitis (EEE) in a 45 year-old woman that resided in Evanston. This is the first record of a human case of this virus for Illinois. Birds, however, have been found infected with the virus in past years. EEE belongs to the

Togaviridae family of viruses, which also includes Western Equine encephalitis, Venezuelan Equine encephalitis, Ross River and Chikungunya. EEE primarily is found in the north-central U.S. and especially along the Atlantic and Golf Coasts.

Human cases of this virus generally occur between May and August. This virus has a much higher mortality rate (50-70%) than WNV and tends to strike both children and older adults. Symptoms of this disease include: fever, stiff neck, stupor, disorientation, tremors, coma and convulsions. Death typically occurs in 2-10 days and those that recover from the more severe form of the disease usually have, progressive, disabling mental and physical complications. Horses are also susceptible to EEE at comparable mortality rates. Similar to WNV, EEE has been associated with bird die-offs but it is not certain if it is the cause of such deaths during outbreaks. Woodchucks and cottontail rabbits are highly susceptible to EEE and usually die from the virus when experimentally infected.

The primary mosquito responsible for sustaining EEE in freshwater swamp areas is Culiseta melanura. This mosquito is reported primarily from southern Illinois and has never been captured in our District. It feeds almost exclusively on birds and is responsible for amplifying the virus in bird populations. It has been reported that other species of mosquitoes may act as the bridge vector transmitting the virus to humans. Some of these suspect human bridge vectors are found in our District (i.e. Coquillettidia perturbans, Culex spp. and Aedes spp.), however, without the presence of Cs. melanura to drive the bird infections it is unlikely that an extensive outbreak would occur. The woman that was reported infected with EEE also spent time in Wisconsin prior to the onset of her infection. Cs. melanura is not uncommon in WI.

MOSQUITO VIRUS SURVEILLANCE IN ILLINOIS

NWMAD has tested 608 mosquito batches to date for West Nile Virus, St. Louis encephalitis and Eastern Equine encephalitis. Two Culex batches from the western portion of Northbrook have tested positive for WNV collected on 06/24-06/26/03, 07/21/03 and one batch from Wheeling collected on

06/30-07/02/03. Mosquitoes testing positive in the District will be posted in this Newsletter as well as the NWMAD website www.nwmadil.com.

The Illinois Department of Public Health reports that 12 batches of mosquitoes have tested positive for WNV in Illinois (4 from Cook County).

BIRD SURVIELLANCE INFORMATION:

As of this writing 18 birds have tested positive for WNV in Illinois according to the Illinois Department of Public Health. Five birds testing positive for WNV were collected in Cook County (Skokie, Oak Park, Evergreen Park, Chicago). 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.

NWMAD has received 565 dead bird reports via website dead bird reporting. The dead bird reporting site is at: http://www.nwmadil.com/Dead Birds.html. Currently no birds have tested positive for WNV in the District.

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, loose fitting, 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 unnecessary 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 large stagnant water areas that remain wet for more than 7 days.

Mike Szyska

Director

PLEASE FORWARD THIS INFORMATION TO APPROPRIATE DEPARTMENTS AND AGENCIES.