July 2, 1998

SPRINGFIELD, IL — The Illinois Department of Public Health today reported that its early warning system for possible mosquito-borne disease activity has detected evidence of encephalitis in birds in Cook and DuPage counties.

Blood samples from one bird collected on June 3 in central Cook County was positive for St. Louis encephalitis (SLE). Also, one blood sample collected on June 5 from a bird in DuPage County tested positive for eastern equine encephalitis (EEE). No human cases of illness from either virus have yet been reported.

"These positive bird samples are an early warning that encephalitis may become a problem in the area," said Dr. John R. Lumpkin, state public health director. "We do not believe this information indicates a need for undue alarm, but persons – particularly those living in the Chicago metropolitan area – should increase their awareness, surveillance and prevention activities."

The Department annually collects blood samples from birds to determine if arboviruses are present in an area. Mosquitoes pick up the virus when feeding on infected birds and then pass the infection on to humans when biting.

Thus far in 1998, the Department has collected 1,370 samples from birds in 20 Illinois counties. In addition, the Chicago Department of Public Health has collected samples from 182 birds this year. In 1997, IDPH collected 4,109 samples; only one was positive for EEE. Counties are selected as collection sites based on the history of virus activity in those areas.

Only three cases of SLE have been confirmed in Illinois residents since 1992. There have been no confirmed cases of EEE in humans in Illinois. Doctors, hospitals and local health departments have been notified of the possibility of encephalitis and asked to be alert to persons with symptoms of the viruses.

Two types of encephalitis are most common in Illinois: St. Louis encephalitis, which is more common among older adults, and LaCrosse encephalitis, which generally strikes children. Both illnesses are characterized by similar symptoms, which range from a slight fever or headache to rapid onset of severe headache, high fever, muscle aches, stiffness in the back of the neck and disorientation. Symptoms usually appear five to 15 days following the bite of an infected mosquito.

EEE, which is carried by marshland and wetland mosquitoes, is primarily a disease of horses. Although the virus can infect humans, cases are extremely rare – only about five are reported annually in the United States.

Dr. Lumpkin emphasized that the first and best defense against mosquitoes and the illnesses they carry is to eliminate the places where they breed. Here are some suggestions:

• Remove or empty water in old tires, tin cans, buckets, drums, bottles or other places where mosquitoes might breed. Be sure to check clogged gutters and flat roofs that may have poor drainage. Make sure cisterns, cesspools, fire barrels, rain barrels and trash containers are covered tightly with a lid or with 16-mesh screen.
• Empty plastic wading pools at least once a week and store indoors when not in use. Unused swimming pools should be drained and kept dry during the mosquito season.
• Change the water in bird baths and plant pots or drip trays at least once each week.
• Store boats covered or upside down, or remove rainwater weekly.
• Empty your pet's water bowl daily.
• Level the ground around your home so water can run off and not collect in low spots. Fill in holes or depressions near your home that accumulate water.
• Fill in tree rot holes and hollow stumps that hold water.
• If you have an ornamental water garden, stock it with mosquito-eating fish such as minnows, "mosquito fish," goldfish or guppies.
• Keep weeds and grass cut short; adult mosquitoes look for these shady places to rest during the hot daylight hours.
• Use a flyswatter or household spray to kill mosquitoes, flies or other insects that get into buildings.
• Some mosquito control methods are not very effective. Bug zappers are not effective in controlling biting mosquitoes. Various birds and bats will eat mosquitoes, but there is little scientific evidence that this reduces mosquitoes around homes.
• Community-wide mosquito abatement programs can be quite effective if they are conducted as integrated pest management programs. The control program should emphasize monitoring and draining or treating areas where mosquitoes breed – such as occasionally flooded marshes, river backwater areas, swamps and other low-lying areas – treating catch basins and removing water-filled containers like old tires.

Personal protection is also important. There are a number of ways people should protect themselves, particularly if they plan to participate in outdoor activities during times when mosquitoes are active.

• Be sure door and window screens are tight-fitting and in good repair.
• Wear appropriate clothing. Long-sleeved tops and long pants made of tightly woven materials keep mosquitoes away from the skin. Be sure, too, that your clothing is light colored. Keep trouser legs tucked into boots or socks.
• Use mosquito netting when sleeping outdoors or in an unscreened structure.
• Check to see that your mosquito repellent contains DEET, a chemical commonly found in these products. Generally, repellents with about 30 percent DEET work best for adults; use lower concentrations for children. When outdoors, apply repellent sparingly to exposed skin or clothing, as indicated on the product's label.

Illinois Department of Public Health 535 West Jefferson Street Springfield, Illinois 62761 Phone 217-782-4977 Fax 217-782-3987 TTY 800-547-0466 Questions or Comments