West Nile is the name of a virus that causes encephalitis, or swelling of the brain. It was previously found only in Africa, western Asia, Middle East, and the Mediterranean regions of Europe. The first case in the United States was reported in 1999.
The virus affects the nervous systems. Symptoms include stumbling, being uncoordinated, weakness of limbs, partial paralysis, muscle twitching and death. Less than one fourth of reported cases in horses involved a fever. Many horses that contract the virus show little symptoms and make full recoveries. Others are not so lucky.
People can also contract the virus. Most will suffer only mild fever and headache before making a full recovery. However, it can be very serious and has caused fatalities in the elderly.
The virus is carried by infected birds, and is transmitted by mosquitoes after biting the infected birds. It can not be contracted from one horse to another. Even if the first horse is infected, it is not able to host the virus for another mosquito to pick it up and transmit it. It can not be transmitted from horses to people either. Researchers are not sure if chickens can spread the virus.
In 1999 there were 25 reported equine cases of West Nile. All of them were reported in the New York area between the months of August and October. In 2000, there were 60 reported cases in New York, Rhode Island, New Jersey, and Connecticut. Most of them also occurred between August and October. On average 38% of cases in the first two years resulted in deaths. As of September 2001, there are already 66 reported cases. Affected areas include Connecticut, Florida, Georgia, Kentucky, Louisiana, Virginia, Massachusetts, Mississippi, New York, and Pennsylvania. Of these 66 cases, 17 horses (26%) died or were euthanized.
The occurrence of the disease during the months of August through October seems to correlate to the migration patterns of birds. In addition to the states reporting equine cases, Ohio, Indiana, Michigan, Wisconsin, Illinois, Maine, Iowa, North Carolina and Tennessee, also report finding infected birds.
