The Monroe County Health Department collected a mosquito batch that tested positive for West Nile virus on June 29 in Waterloo.

West Nile virus activity is largely dependent on the weather and as the summer’s temperatures rise, mosquitoes carrying West Nile virus are more active. Weeks of rain and flooding in southern Illinois have made conditions ripe for mosquitoes.

Floodwater mosquitoes typically appear approximately two weeks after heavy rains and flooding. While a floodwater mosquito can be a vicious biter, a nuisance and will commonly fly 10 or more miles from where it hatched, these mosquitoes have not been significant disease carriers to humans in Illinois.

However, as floodwaters recede into ditches, catch basins or other areas where the waters sits stagnant, house mosquitoes will find these conditions optimal for egg laying and do not travel long distances. House mosquitoes can be infected with the West Nile Virus.

Eggs are laid on or just above the water surface, where they usually hatch within two to three days.  The West Nile virus is transmitted through the bite of a mosquito that has picked up the virus by feeding on an infected bird. Most people with the virus have no clinical symptoms of illness, but some may become ill three to 15 days after the bite of an infected mosquito.

Common symptoms include fever, nausea, headache and muscle aches.  Symptoms may last from a few days to a few weeks. However, four out of five people infected with West Nile virus will not show any symptoms. In rare cases, severe illness including meningitis or encephalitis, or even death, can occur. People older than 50 and immunocompromised individuals are at higher risk for severe illness from West Nile Virus.

The Monroe County Health Department continues to conduct surveillance for West Nile virus in the county with testing of mosquito batches, dead crows, blue jays, robins and other perching birds. People who observe a sick or dying crow, blue jay, robin or other perching bird should contact  the health department to determine if the bird will be picked up for testing.

What is the best way to reduce populations of mosquitoes?

The first and best defense against these pests and the illnesses they may carry is to eliminate the places where they breed. Here are a few suggestions:
• Remove or empty water in old tires, tin cans, buckets, drums, bottles or other places where mosquitoes might breed. Check clogged gutters and flat roofs that may have poor drainage. Make sure cisterns, cesspools, septic tanks, 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 covered or drained during the mosquito season. (Note: If you choose to drain your pool, be sure the hydrostatic relief valve is open in order to keep it from floating out of the ground if the water table rises.)
• Change the water in bird baths and plant pots or drip trays at least twice 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 (e.g., minnows, “mosquito fish,” or goldfish). They eat mosquito larvae.
• Keep weeds and tall 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. Spray shrubbery and high weeds to kill adult insects. (Check the insecticide label to make the sure the spray will not damage flowers or ornamental plants.)
• 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.

How can people protect themselves from mosquito bites?  People can continue to enjoy the outdoors by taking personal precautions to prevent from being bitten:

• Avoid places and times when house mosquitoes bite. Generally, the peak biting periods occur just before and after sunset and again just before dawn. Each species, however, has its own peak period of biting. Tree-hole and Asian tiger mosquitoes, for example, feed during daylight hours in or near shaded or wooded areas.
• 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 and to protect small babies any time.
• When it is necessary to be outdoors, apply insect repellent as indicated on the repellent label. The more DEET a product contains, the longer the repellant can protect against mosquito bites. However, concentrations higher than 50 percent do not increase the length of protection. For most situations, 10 to 25 percent DEET is adequate. Apply repellents to clothes whenever possible; apply sparingly to exposed skin if label permits. Consult a physician before using repellents on young children.

Additional information about West Nile virus can be found at: www.dph.illinois.gov/topics-services/diseases-and-conditions/diseases-a-z-list/west-nile-virus.