WILLMAR -- Health officials are urging Minnesotans to watch out for mosquitoes, now that the West Nile virus season is officially here.
The peak time for West Nile virus, which is transmitted by mosquitoes, runs from July through September.
The first three cases this year in Minnesota were announced Monday. The Minnesota Department of Health said they occurred among a man in his 60s who lives in Clay County, and two individuals from Becker and Carver counties, both under the age of 20.
All three developed symptoms of West Nile virus in early to mid-July and were later diagnosed with West Nile fever, a milder form of illness.
They are now recovering, the state Health Department said Monday.
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Cool weather meant less mosquito activity during the early summer, said Chris Wenisch, director of environmental health programs for Kandiyohi County Public Health.
This has changed with the recent heat and rain, which favors mosquito production, he said.
"They're hatching."
Although West Nile virus occurs throughout Minnesota, the risk is highest in the western and central part of the state, where the highest numbers of the Culex tarsalis mosquito are found. Culex is the primary carrier of West Nile virus in Minnesota.
Precautions can help lower the risk of being bitten, Wenisch said.
"If you're going to go outside, especially at dusk, we recommend wearing long sleeves and long pants," he said.
Repellents that contain DEET should be used by adults, he said. Alternative products also are available that are safe for children.
State health officials said this is the No. 1 preventive strategy people can take.
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"The key to avoiding West Nile virus illness is to keep repellent on hand from July through September, and to use it diligently," Dave Neitzel, a Minnesota Department of Health epidemiologist specializing in mosquito-borne and tick-borne diseases, said in a statewide news release issued Monday.
Homeowners also should take steps to make their yard less inviting for mosquitoes, Wenisch advised.
"It's really important to get rid of standing water. That's where they're laying their eggs," he said.
Birdbaths should be regularly emptied and cleaned, and containers such as wheelbarrows and old tires should be emptied or removed. Clogged rain gutters containing stagnant water are another frequent breeding ground for mosquitoes.
Indoors, damaged window screens should be repaired or replaced to keep mosquitoes out, Wenisch said.
Most people who are infected with West Nile virus have no symptoms or develop West Nile fever, the less severe form of the disease.
But about one out of every 150 persons bitten by an infected mosquito will become severely ill with encephalitis or meningitis, and about 10 percent of them will die. Many of those who survive end up with long-term damage to the nervous system.
Symptoms usually appear three to 15 days after being bitten. They can include headache, high fever, rash, muscle weakness, stiff neck, disorientation, convulsions, paralysis and coma.
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Severe cases occur most often among the elderly and among people with weakened immune systems.
Horses also are susceptible to West Nile virus. Before a vaccine became available, as many as 30 percent of horses with West Nile virus later died. Veterinarians now recommend vaccinating horses as a protective measure.
West Nile virus was unknown in North America until 1999, when the first cases appeared on the East Coast. The virus can now be found in the entire contiguous United States.
