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MEDIA RELEASE

May 1, 2003
Contact : Chuck Schwartau, U of M Extension Service Educator (651-385-3100)

West Nile Virus And Mosquito – Transmitted Diseases

Written By Chuck Schwartau, Regional Extension Educator, U of M Ext. Service

West Nile virus (WNV) is a mosquito-transmitted virus that can cause encephalitis in some people. This virus usually circulates between mosquitoes and birds in Africa and Europe. However, in 1999, an outbreak of WN encephalitis was reported in New York City. Since then the virus has spread throughout much of the United States.

In 2002 there were several reported cases of WNV in Minnesota and it is likely that in 2003, WNV will be found in Minnesota again. Fortunately, most people who are bitten by infected mosquitoes will experience either no symptoms, or mild illness. While the risk of WN encephalitis to Minnesotans is small, people can do several things to protect themselves from this virus and other mosquito-transmitted illnesses already found here, such as using mosquito repellents, and eliminating water-holding containers (buckets, tires, etc.) from their property. The Mosquito Control Association (http://www.mosquito.org/mosquito.html) has additional suggestions for controlling mosquitoes and decreasing the risk of acquiring a mosquito-transmitted disease.

The following items give more detail on West Nile Encephalitis and General Mosquito Control that citizens should know:

What is West Nile Virus?

• West Nile Encephalitis is a viral disease transmitted to people and horses through the bite of an infected mosquito.

• West Nile virus (WNV) is maintained in a transmission cycle involving one or more species of mosquitoes and birds. Current research is focusing on which mosquitoes and birds are most important in this cycle.

• WNV is usually found in Africa and southern Europe. The virus was first reported in North America during a 1999 outbreak of encephalitis in New York City.

How serious is West Nile virus?

• Most people infected with WNV will have either no symptoms or a very mild illness. A small percentage of people, especially elderly patients, may develop encephalitis (inflammation of the brain). Approximately 13% of these encephalitis cases are fatal.

West Nile Virus and Other Mosquito-Transmitted Diseases

• Most of the severe human cases of WN encephalitis begin with sudden onset of fever, headache, stiff neck, and vomiting. The illness progresses quickly to include confusion and other mental status changes, altered reflexes, convulsions, and coma. There is no treatment for WN encephalitis other than supportive care.

• Approximately 33% of symptomatic horses are put down or die from WNV infections.

What is the risk of a West Nile Encephalitis outbreak in Minnesota?

• With our abundant mosquito and bird populations, we expect that WNV will be in Minnesota. Similar to other mosquito-transmitted diseases already established in this area (LaCrosse encephalitis, Western equine encephalitis, and Eastern equine encephalitis), WNV will likely cause sporadic illness in humans (especially elderly people) and horses.

What can people do to prevent West Nile Encephalitis?

• Personal protection measures such as use of mosquito repellents, avoiding outdoor exposures at dusk and dawn (peak feeding time for many mosquitoes), and wearing long-sleeved shirts and long pants can reduce the risk of WN encephalitis.

• Removal of water-holding containers (mosquito breeding sites) from residential areas will reduce numbers of several mosquito species.

• There is a vaccine available for horses to prevent WN encephalitis. Please contact your veterinarian for vaccine recommendations. A human WNV vaccine is in development.

How can I help look for West Nile virus?

• The first indication of WNV in an area is usually an outbreak of the disease in wild bird populations. If you find dead birds during the summer months (especially July-September), please report them to the Minnesota Department of Health at (612) 676-5414. MDH staff will record the details of where and when the birds were found, and some may be tested for the virus.