What is the West Nile virus?

The West Nile virus belongs to a group of viruses known to cause encephalitis, a potentially fatal inflammation of the brain and spinal cord. The West Nile virus is known to affect horses, birds and humans.

How does the virus spread?

Birds serve as the host for the virus, which is spread by mosquitoes to other birds and animals. West Nile has been identified in nearly 100 species of birds, with blue jays and crows seeming to be especially susceptible. There are no known cases of transmission from person to person or from birds or mammals to humans.

Where is the virus found?

The virus was discovered in Africa decades ago, and was first detected in North America in 1999 during an outbreak in New York. Since then, West Nile infections have been confirmed across much of the eastern and southern United States. In recent weeks, cases have been reported in birds and horses in North Dakota, Texas, Oklahoma and Nebraska. The virus has also been found in birds in Wisconsin and Iowa.

How common are West Nile virus infections in horses?

A total of 733 equine cases of West Nile virus were reported in 2001. The majority of these cases have been found in Florida.

What are the symptoms of West Nile infections in horses?

Horses may develop lethargy, hindquarter weakness, involuntary muscle contractions, loss of coordination, head tilt, circling, convulsions, paralysis, and coma. Horse owners should contact their veterinarian if they notice any symptoms of the disease.

Only supportive care can be offered to infected horses. While most infected horses recover, nearly one-third of equine West Nile virus cases result in the death of the horse.

Is there a vaccine available for horses?

Yes. A West Nile virus vaccine for horses has been granted a conditional license by the USDA. It is recommended that vaccination be completed at least three weeks before the mosquito season, and repeated annually. Keep in mind that horse vaccines such as Western or Eastern Equine Encephalitis vaccine will not protect against West Nile. Contact your veterinarian for more information.

What can horse owners do to protect their animals?

Horse owners can try to reduce the mosquito population around their horses by taking the following steps:

• eliminate "mosquito zones" by mowing long grass, draining stagnant water puddles, and removing items such as old tires and tin cans that can serve as breeding grounds for mosquitoes;
• minimize your horses' exposure by using repellants and placing screens in stables; and
• ask your veterinarian about vaccinating your horses with West Nile virus vaccine. The vaccine must be administered twice within a three to six-week period to be effective.

What is the Minnesota Board of Animal Health doing about West Nile virus?

Since the discovery of West Nile virus in North America, the Minnesota Board of Animal Health and the Minnesota Department of Health have worked together to watch for signs the virus has entered Minnesota. State law requires veterinarians to report any cases of West Nile virus or other equine encephalitis to the Board. The Board works with local veterinarians to investigate cases of West Nile virus in horses. The Board also has taken steps to educate Minnesota veterinarians and horse owners about West Nile and what they can do to protect their animals.

What about the risks to humans?

The chance that a human will become severely ill from any one mosquito bite is low. Even in areas where mosquitoes do carry the virus, less than 1 percent of mosquitoes are infected. Beyond that, less than 1 percent of the humans bitten by an infected mosquito get sick. However, in rare cases, severe illness or death can result from a West Nile virus infection. As of July 18, 2002, the Centers for Disease Control and Prevention (CDC) had confirmed 152 total human cases of West Nile virus in the United States, including 18 fatalities.

Are dogs and cats at risk?

According to the CDC, West Nile virus does not appear to cause extensive illness in dogs or cats.

Where can I go for more information?

For more information about West Nile prevention for horses, visit the Minnesota Board of Animal Health web site or the U.S. Department of Agriculture's web site. Information on prevention and vaccination information is also available on the University of Minnesota College of Veterinary Medicine web site.

More information about humans and the West Nile virus is available on the Minnesota Department of Health's web site.