Issue 15, August 27, 2012

West Nile Virus

The hot, dry summer has apparently been responsible for higher levels of West Nile virus earlier this year in Illinois. The virus is reaching levels about a month earlier than is typical. As it normally builds from mid-August through the fall, this early increase followed by human cases makes it likely that its impact will be much higher than recent years. This increased level makes it important to protect landscape workers and others involved in outdoor activities.

The first Illinois human fatality in 2012 has been reported from northern Illinois by the Illinois Department of Public Health (IDPH). A DuPage County man in his 70s, who had underlying health conditions, was diagnosed with West Nile virus earlier this month and died last weekend. The first human case of West Nile virus was reported in Southern Illinois. A Crawford County woman in her 80s tested positive for West Nile Virus.

There are record levels of West Nile virus activity nationwide and very high mosquito activity in Illinois. Through the second week in August, 693 cases had been reported to the Centers for Disease Control and Prevention (CDC). That is the highest number of West Nile virus disease cases reported to CDC through the same period since West Nile virus was first detected in the U.S. in 1999. More than 80 percent of the cases have been reported from six states (Texas, Mississippi, Louisiana, Oklahoma, South Dakota, and California).

IDPH currently is reporting 21 human cases of West Nile virus in Illinois. The first human case of West Nile virus was reported on July 24--about a month earlier than most human cases in previous years. There were 34 human cases for the entire year in 2011. So far this year, 38 counties have reported mosquito batches, birds or people testing positive for West Nile virus.

West Nile virus is transmitted through the bite of a mosquito that has picked up the virus by feeding on an infected bird. Common West Nile virus 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 are at higher risk for severe illness from West Nile virus.

Landscapers and other workers should protect themselves from bites and make suggestions to clientele to reduce the number of mosquitoes. Avoid being outdoors when mosquitoes are most active, especially between dusk and dawn. When outdoors, wear shoes and socks, long pants and a long-sleeved shirt, and apply insect repellent that contains DEET, picaridin, oil of lemon eucalyptus or IR 3535, according to label instructions. These repellents should provide about two hours of protection. Other repellents may be effective, but usually do not last as long, with many organic products being effective for only about 20 minutes, requiring frequent reapplication.

The northern house mosquito, Culex pipiens, that transmits West Nile virus and St. Louis encephalitis from birds to humans and other mammals breeds in smelly, stagnant water. The adults typically do not fly more than half a mile, so neighborhood mosquito reduction efforts can greatly decrease the likelihood of being infected.

Northern house mosquito adult.

While doing landscape work, advise clientele about mosquito breeding sites that they can address. Clientele should eliminate all sources of standing water where mosquitoes can breed, including water in tree holes, gutters, old tires, and other items that hold water. Bird baths, wading pools, and flowerpot dishes should be dumped and rinsed weekly before refilling.

Garden pools should contain goldfish, bait minnows, or other fish that will eat mosquito larvae. Koi, being ornamental carp, do not feed enough on mosquito larvae to be effective biological control agents. Garden pools without fish or only containing koi should be treated with Bacillus thuringiensis israeliensis available as donuts, briquettes, granules, or other slow release forms that provide mosquito larval control for a month or more.

Additional information about West Nile virus can be found on the IDPH website. Surveillance numbers are updated on the IDPH website as well. (IDPH news release modified and added to by Phil Nixon)

Phil Nixon

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