From Birds to Mosquitoes to Us: West Nile Virus Season Begins

The increasing range of West Nile Virus (WNV) tells us the disease is now permanently established in the United States. The virus was first identified in 1937 in the West Nile region of Uganda, but it hadn't been reported in North America until the summer of 1999, when it was found in the New York City area. In that year, 62 people were hospitalized with the infection and 7 died.

By the summer of 2006, the Centers for Disease Control and Prevention (CDC) reported 4,256 WNV cases nationwide, with 165 deaths. Medical facilities typically start seeing infections in July and the case count tends to peak in August and September.

Although no human cases of West Nile virus have been reported in Wisconsin yet this year, 13 cases, with one death, occurred in 2007. Almost every state now reports human cases of WNV. Nationwide, 3,630 human cases were reported last year, with 124 deaths.

How the Virus Spreads
Most often, WNV is spread by infected mosquitoes. Mosquitoes become infected when they feed on infected birds, and can then spread WNV to humans and other animals when they bite.

In a very small number of cases, WNV has been spread through blood transfusions, organ transplants, breast feeding or during pregnancy from mother to baby. The risk of contracting WNV through medical procedures is extremely low, and should not prevent people who need surgery from having it. All donated blood is checked for WNV before being used.

WNV is not spread through casual contact such as touching or kissing a person with the virus.

Symptoms
It takes from 3 to 15 days after being bitten by an infected mosquito for symptoms to appear. Most people (about 80%) who are infected will not show any symptoms at all.

Up to 20% of people who become infected have symptoms such as fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Milder WNV illness improves on its own, and people do not necessarily need to seek medical attention.

About one in 150 people infected with WNV will develop severe illness. Symptoms might include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness, and paralysis. These symptoms can last several weeks, and neurological effects could be permanent.

As with many illnesses, the elderly and those with weakened immune systems run the highest risk of severe disease. Pregnant women and nursing mothers are encouraged to talk to their doctor if they develop symptoms that could be WNV.

If you develop symptoms of severe WNV illness, seek medical attention immediately. Severe WNV illness usually requires hospitalization. Although here is no specific treatment for WNV infection, people with severe symptoms usually need supportive treatment including intravenous fluids, breathing assistance, and nursing care.

Prevention
The easiest and best way to avoid WNV is to prevent mosquito bites. Taking a few common-sense steps will greatly reduce your chances of being infected:

• Use insect repellant containing one of the active ingredients registered by the Environmental Protection Agency (EPA). Of these, two have demonstrated a higher degree of efficacy in the peer-reviewed, scientific literature: DEET (N,N-diethyl-m-toluamide) and Picaridin (KBR 3023) typically provide longer-lasting protection than the others. Repellants containing oil of lemon eucalyptus [p-menthane 3,8-diol (PMD)], a plant-derived active ingredient, are also registered with EPA, as are those using IR3535 (3-[N-Butyl-N-acetyl]-aminopropionic acid, ethyl ester).
• Many mosquitoes are most active at dusk and dawn. Be sure to use insect repellant and wear long sleeves and pants at these times or consider staying indoors during these hours.
• Make sure you have good screens on your windows and doors to keep mosquitoes out.
• Reduce mosquito breeding areas by getting rid of any standing water. Empty water from flower pots, buckets, and barrels. Change the water in pet dishes and replace the water in bird baths weekly. Keep children's wading pools empty and on their sides when they aren't being used. Drill holes in tire swings so water drains out. (In Milwaukee, if you have 5 or fewer waste tires to dispose of, call the Department of Public Works at 414-286-8282.)

Even though WNV is only transmitted by the mosquitoes that feed on birds and animals (not by the birds and animals themselves), health experts urge people to stay away from dead birds or animals when possible, wear rubber gloves if you need to handle them, or dispose of the bodies without touching them.

Since 1999, corvids (e.g., crows, jays, and magpies), have accounted for more than 70% of all WNV-infected dead birds reported to CDC.

If you find a sick or injured bird, contact your local Humane Society or Health Department. In Wisconsin, call 414-ANIMALS [264-6257]. In addition, the City of Milwaukee Health Department is asking people to call 414-286-3521 to report a dead bird.

This article includes information from the Centers for Disease Control and Prevention and the CDC's Morbidity and Mortality Weekly Report.

Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.