Minnesota reports first West Nile virus case of 2013

The first human case of West Nile virus (WNV) disease in 2013 has been reported in a Minnesota resident. The Murray County man became ill with West Nile fever earlier this month and is recovering. State health officials are urging Minnesotans to protect themselves from mosquitoes.

West Nile virus is a potentially life-threatening disease and Minnesotans should protect themselves by routinely using mosquito repellents and taking other simple precautions against mosquito bites, Minnesota Department of Health (MDH) officials said.

David Neitzel, an MDH epidemiologist specializing in diseases carried by mosquitoes, said that we have now entered the high risk season for WNV which continues through early autumn. “The species of mosquito that transmits the virus to humans is most abundant in July and August. Mosquito repellents used during outdoor activities at dusk and dawn can prevent this potentially severe disease.”

About 1 out of 150 people bitten by a WNV-infected mosquito will develop central nervous system disease (encephalitis or meningitis). Approximately 10 percent of people with this severe form of infection die from their illness, and survivors can suffer from long-term nervous system problems. Fortunately, most people bitten by infected mosquitoes develop West Nile fever, the less severe form of disease, or fight off the virus without any symptoms.

Illness from WNV can occur in residents throughout Minnesota and among all age groups. However, WNV risk is greatest in western and central counties, which typically have the greatest number of Culex tarsalis mosquitoes, the primary mosquito carrier of the virus in Minnesota. Elderly people or people with weakened immune systems face the highest risk of developing the more severe or even fatal illness from a WNV infection. “They need to be especially diligent about protecting themselves from mosquitoes,” Neitzel noted.

People can reduce their chance of WNV infection by using mosquito repellents at dusk and dawn when these mosquitoes are most active. Several safe and effective options are available:

Repellents containing DEET (up to 30 percent concentration) are safe and effective at providing protection against mosquito bites.
Permethrin is a strong repellent and will kill mosquitoes that come into contact with treated clothing. Repellents containing permethrin are applied to clothing (not skin). Treated clothing can be worn after the repellent dries.
Additional options include repellents containing picaridin, oil of lemon eucalyptus, or IR3535.
For maximum effectiveness and safety, all mosquito repellents should be used according to label directions.
Other important steps to prevent mosquito bites and potential illness from WNV include:

Minimize outdoor activities at dusk and dawn, as this is prime feeding time for WNV-carrying mosquitoes. If you go outside at these times, take precautions even if mosquito numbers seem low; it only takes one bite from an infected mosquito to transmit the virus.
Wear loose-fitting, long-sleeve shirts and long pants if you must spend time in an area where mosquitoes are biting.
Culex tarsalis mosquitoes, which carry WNV, prefer open, agricultural areas of central and western Minnesota and other Great Plains states. While the majority of Minnesota’s WNV disease has occurred in people from these areas, cases are possible anywhere within the state. Since WNV was first found in Minnesota in 2002, 535 cases (including 16 fatalities) of WNV disease have been reported to MDH.

Symptoms of WNV disease usually begin 3 to 15 days after being bitten and can include headache, high fever, rash, muscle weakness, stiff neck, disorientation, convulsions, paralysis and coma.

Information on WNV can be found at the MDH website: http://www.health.state.mn.us/divs/idepc/diseases/westnile/index.html and at the CDC website: http://www.cdc.gov/ncidod/dvbid/westnile/RepellentUpdates.htm.

People who have questions about WNV can call MDH at 651-201-5414 or 1-877-676-5414 (outstate) between 8 a.m. and 4:30 p.m. Monday through Friday.

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