West Nile Encephalitis

What is West Nile Virus?
Encephalitis means in infection of the brain that can be caused by viruses and bacteria, including viruses transmitted by mosquitoes. West Nile Encephalitis is an infection of the brain caused by West Nile Virus, a flavivirus commonly found in Africa, west Asia, Eastern Europe, and the Middle East. It is closely related to St. Louis encephalitis virus found in the US.

How long has it been in the US?
Before 1999 West Nile virus had never been reported in the US or anywhere else in the Western Hemisphere. In August 1999, 62 cases of severe disease and 7 deaths occurred in New York. No reliable estimates are available for the number of cases of West Nile virus that occur worldwide. It is not known where the US virus originated, but it is most closely related to strains found in the Middle East.

How do people get West Nile virus?
The virus is transmitted by the bite of an infected mosquito, primarily the Culex species. The virus is NOT transmitted from person to person. You cannot contract the virus from touching or kissing a person who is infected, or from a health care worker who has treated someone with the disease.

Following transmission, the virus multiplies in the person's blood system and crosses the blood-brain barrier to reach the brain. The virus interferes with normal central nervous system functioning and cases inflammation of brain tissue. The incubation period (time from infection to the onset of disease symptoms) is usually between 5 and 15 days.

What are the symptoms?
Most infections are mild and the symptoms include fever, headache, body aches, often with skin rash and swollen lymph glands. More severe infection may be marked by headache, fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, paralysis, and rarely, death. Case fatality rates range from 3% to 15% and are highest in the elderly.

Can you get West Nile Virus from birds?
There is no evidence that a person can get the virus from handling live or dead infected birds. However you should avoid bare-handed contact when handling dead animals, including dead birds. Use gloves or double plastic bags to place the carcass in a garbage can.

Can other animals get the virus?
Animals, including cats and dogs, wild or domesticated fowl and game animals, and horses can be infected the same way as humans. There is no documented evidence of animal-to-animal transmission, but precautions should be taken with animals. Care should be taken to keep animals from mosquito infested areas.

Hunters should check with their local department of wildlife and natural resources, the state health department, the US Geological Survey, or the National Wildlife Health Center in Madison, WI (telephone 608-270-2400) for information about risk in their areas.

How can we prevent infection with the virus?
There is no approved vaccination currently available for West Nile Virus. To reduce your risk of becoming infected, take these steps to avoid mosquito bites:

• Stay indoors at dawn, dusk, and in the early evening when mosquitoes are most active.
• Wear long-sleeved shirts and long pants when you are outdoors.
• Apply insect repellant to clothing and only very sparing to skin. Effective repellants contain 20% to 35% DEET. Do not use products with more than 35% DEET - they can cause side effects - especially in children.
• NEVER apply insect repellants to children under 3 years old.
• Never put repellant on a child's hands - this increases the risk of getting it into their eyes and mouth.

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.