Determined To Be The Cause Of Human And Equine Illnesses In New York City

For the first time, West Nile virus–or a new subtype of that virus–has been confirmed in humans and horses in the United States. The outbreak of encephalitis-like sickness in humans in New York City now has been verified as caused by West Nile virus. This is the first confirmed evidence of West Nile virus infection in the Western Hemisphere. There have been 39 cases of West Nile virus confirmed in humans in New York City, and six deaths attributed to the disease (mostly in older persons). There are more than 168 cases under investigation.

The virus is suspected in wild bird populations in New Jersey and Connecticut. In New Jersey, cases of a similar virus, Saint Louis encephalitis, have been confirmed in both dead crows and homing pigeons. The birds have been sent to the national Centers for Disease Control (CDC) and are under testing for West Nile virus. West Nile is a mosquito-borne (possibly arthropod-borne) virus that belongs to the Flavivirus family. The virus is included in the Saint Louis encephalitis subgroup of viruses that also includes Japanese encephalitis, Murray Valley encephalitis, and Kunjin encephalitis. (The latter two viruses are found in Australia.) Initially, doctors in New York thought the outbreak of illness was due to Saint Louis encephalitis virus.

The principal species involved in the maintenance of West Nile virus is wild birds–which act as hosts for the virus–and domestic quadrupeds, such as horses.

It should be noted that horses are considered tangential or dead-end hosts of the virus and are very unlikely to play a role in spread of the disease. Horses can become infected with the virus and develop neurologic signs since the virus can invade the spinal cord and brain