Be Vigilant About West Nile Virus

By Jeff Bender, D.V.M., M.S.

Increased concern about the spread of the West Nile virus has become part of summer in Minnesota. West Nile virus is classified as zoonotic, meaning the disease originated in animals and was subsequently transmitted to humans, generally by mosquitoes. The virus mainly causes disease in humans, birds, and horses.

West Nile virus was first identified in 1937 in the West Nile district of Uganda after a woman developed fever that was eventually linked to virus-infected mosquitoes. The virus wasn't detected in the United States until 1999 when a doctor in New York noticed several people living in the same neighborhood with a similar and unusual symptom of swelling in the brain. During the same period, a zookeeper at the Bronx Zoo noticed an unusually high number of ill zoo animals and dead crows around the zoo.

West Nile virus has now been detected in nearly every state. The first West Nile case in Minnesota was in 2002. Although 48 human West Nile cases were reported last year, no one in Minnesota has died. As of Aug. 26, 2003, 13 people have become ill with West Nile virus in Minnesota.

Mosquitoes serve as the primary transmitter of the virus. They become infected with West Nile virus after feeding on infected birds. The mosquito then transmits the virus through feeding on (biting) humans, horses, and other birds and mammals. It also was observed that some people became ill after blood transfusions or organ transplantation, prompting new blood-screening procedures.

The good news is that most people who are infected with the West Nile virus do not become sick. Those who do become ill usually suffer only flu-like symptoms that go away in a few days. Very few people develop a severe infection, West Nile encephalitis, which symptoms include high fever, neck stiffness, headache, and neurological problems.

There are many preventive measures that can help people avoid becoming infected with West Nile virus. First, reduce mosquito-breeding habitats. This includes all standing water in and around the yard. Second, use repellents that contain DEET. It is a safe product that keeps mosquitoes away better than anything else. Third, avoid outdoor activities at dawn and dusk the time when mosquitoes are most active.

People over the age of 50 should pay close attention to these precautions. This age group is the most susceptible to developing severe disease.

It is also important to keep in mind that the West Nile virus season didn't end with Labor Day. In fact the peak season for the virus is mid-August through mid-September. Don't be complacent about prevention efforts during this crucial time.