West Nile Virus is Here to Stay

West Nile virus (WNV) was first discovered in 1937 in the West Nile area of Uganda, but it didn't make its way to 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.

Fast-forward to the summer of 2006, when the Centers for Disease Control and Prevention (CDC) reported 4,256 WNV cases nationwide, with 165 deaths.

According to Rick Gillis, MD, Medical College of Wisconsin Assistant Professor of Medicine, the increasing range of West Nile Virus tells us the disease is permanently established in the United States.

Although no human cases of West Nile virus have been reported in Wisconsin yet this year, 21 cases, with one death, occurred in 2006 and the City of Milwaukee Health Department identified 90 pools of mosquitoes carrying WNV.

Although there may be a few infections reported through the year, medical facilities typically start seeing infections in July and the case count tends to peak in August and September.

How the Virus Spreads
Most often, WNV is spread by the bite of an infected mosquito. 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, breastfeeding and even 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, help with breathing, 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 repellent 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. Repellents containing oil of lemon eucalyptus [p-menthane 3,8-diol (PMD)], a plant-derived active ingredient, are also registered with EPA.
• Many mosquitoes are most active at dusk and dawn. Be sure to use insect repellent 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. Drill holes in tire swings so water drains out. Keep children's wading pools empty and on their sides when they aren't being used. (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 either to stay away from dead birds or animals, handle the bodies without touching them, or wear rubber gloves when handling sick or dead birds.

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, please contact the Wisconsin Humane Society 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 was reviewed by Rick Gillis, MD, Assistant Professor of Medicine and Director of the Office of Clinical Informatics at the Medical College of Wisconsin. Dr. Gillis practices at the Sargeant Internal Medicine Clinic.

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.