Minnesota Department of Health

News Release

July 24, 2002

Contact information

West Nile Virus arrives in Minnesota
Crows from two Minnesota counties test positive for WNV, providing the first evidence that virus has reached state

Dead crows from two Minnesota counties have tested positive for West Nile Virus (WNV), providing the first evidence that the mosquito-borne virus has reached Minnesota.

The crows were submitted to the Minnesota Department of Health (MDH) by local officials in Mille Lacs County, and a private citizen in Hennepin County.

MDH has been testing dead birds for WNV as part of its routine surveillance for the presence of the virus in Minnesota. Crows and jays are especially susceptible to the virus, and provide an effective indicator of whether WNV is present in a particular area.

Public health officials throughout the nation have been on the lookout for West Nile since 1999, when the virus first made its appearance in the New York City area. That was the first time WNV had been reported in the U.S.

Since then, WNV has slowly been spreading to other parts of the country, most likely through the migration of birds infected with the virus.

WNV activity has now been reported in 33 states. Since 1999, at least 152 human cases of WNV-related encephalitis have been reported nationwide, and 18 people have died of the illness. People in 10 states have developed the illness during that time, although a majority of those cases have been reported in New York City and surrounding states, and in Florida.

Although MDH officials are recommending that people take steps to protect themselves against West Nile, they say the risk of any individual Minnesotan developing the illness is very small. They also point out that viral, mosquito-borne encephalitis is nothing new in our state.

"This is a serious, potentially fatal illness, and we don't want to underplay its significance," said Dr. Harry Hull, Minnesota's State Epidemiologist. "However, the odds that you'll be bitten by an infected mosquito are very low. And even if you are bitten by a mosquito that carries the virus, it's unlikely that you'll become seriously ill. Most of the time, people don't even experience any symptoms."

Fewer than one person out of every 150 who are exposed to the virus will actually develop encephalitis, Dr. Hull noted.

In that respect, WNV is not that different from LaCrosse encephalitis, which is also caused by a mosquito-borne virus - and has long been recognized as a public health threat in this part of the country. LaCrosse causes around five cases of serious illness a year in Minnesota, primarily in the Twin Cities area and the southeastern part of the state.

Symptoms of a serious mosquito-borne encephalitis infection - which generally occur in less than one percent of people exposed to the virus - can include headache, high fever, stiff neck, stupor, coma, tremors, convulsions, muscle weakness and paralysis.

Both LaCrosse and WNV can be life-threatening. But WNV does differ from LaCrosse in one important way: Serious cases of LaCrosse encephalitis tend to occur in children and adolescents under the age of 16, while serious cases of WNV have so far tended to occur in older people. The average age of patients with a serious WNV infection is 68.

To lower the risk of infection with WNV - or LaCrosse - officials recommend:

• avoiding outdoor activities at dusk and dawn, when mosquitoes are most likely to be feeding;
• wearing long-sleeve shirts and long pants if you have to spend time in an area where mosquitoes are biting;
• protecting yourself with a good mosquito repellent, containing up to 30 percent of the active ingredient DEET; and
• eliminating possible mosquito-breeding sites on and around your property - including items like old tires, buckets, clogged rain gutters, bird baths, cans and other containers, and anything else that can hold a small amount of water.

Minnesota officials stepped up their surveillance for WNV earlier this month, after WNV encephalitis was reported in a horse near Grand Forks, North Dakota.

Like other states, Minnesota has been testing mosquitoes for the virus, and officials have also been on the alert for cases of WNV-related illness in humans, horses and birds. These surveillance activities have been a joint effort of MDH, the Minnesota Board of Animal Health, the Metropolitan Mosquito Control District, the Minnesota Department of Natural Resources, the Veterinary Diagnostic Laboratory at the University of Minnesota, and the U.S. Department of Agriculture.

More information about WNV and other forms of mosquito-borne encephalitis is available on the MDH Web site at www.health.state.mn.us.

-MDH-

For more information, contact:

Buddy Ferguson
MDH Communications
(651) 215-1306

Dr. Harry Hull
State Epidemiologist
(612) 676-5414

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