from the Vet Corner Archives

Veterinary Corner 12/01: West Nile Virus

by Frosty Franklin, DVM
Edgecliff Equine Hospital
S. 1322 Park Road, Spokane, WA 99212 * 509/924-6069


The West Nile Virus (WNV) is carried by mosquitoes and can infect humans, horses, and birds. The clinical signs involve primarily the nervous system, with headache, high fever, disorientation, seizures, coma, and rarely death. In horses, the signs include difficulty walking, staggering, knuckling over, muscle tremors, head tilt and inability to stand.

Prior to 1999 WNV was thought to occur only in Africa, Eastern Europe, and West Asia. In 1999, in New York City 62 human cases of WNV encephalitis were diagnosed and 7 deaths occurred. Twenty-five horse cases were identified in New York between August and October in 1999. Nine horses died, while 16 completely recovered. Blood testing of the 69 stable mates revealed 20 had antibodies to the WNV. Results from a blood survey of the horses in New York City showed 5% of horses had been exposed to WNV. In 2000, 21 confirmed human cases were reported in three states (New York, New Jersey, and Connecticut) including two deaths. Sixty horse cases were reported from seven Northeastern states. As of September 2001, 14 human cases (one fatal) have been confirmed. Sixty-seven equine cases (17 fatal) have been identified in 8 states: Florida (54), Georgia (5), New York (2), Pennsylvania (2), and single cases in Connecticut, Kentucky, Louisiana and Virginia.

Wild birds infected with West Nile Virus can become ill or die. The majority of cases have been observed in crows. However, twenty native bird species have demonstrated infection with the WNV. Thousands of dead wild birds were reported positive for WNV in 2000 in twelve states from New Hampshire to Virginia. This year the WNV has been reported in Canada (Ontario) for the first time. The virus recently has been identified in the midwestern states of Indiana, Illinois, Michigan, Ohio, and Wisconsin based on disease surveillance techniques.

There is no documented evidence of person-to-person, animal-to-animal, or animal-to-person transmission of WNV. Mosquitoes carry the virus. Not every mosquito carries the virus. The WNV has not been found in Washington or nearby states. Continued proper surveillance activities are necessary:

* Report unexplained, unusual numbers of bird deaths, especially crows, jays, ravens, or magpies to the Department of Health at 360-236-3060.

* Physicians on alert for persons with appropriate clinical signs

* Report horses with appropriate clinical signs (clinical signs cannot be distinguished from other viral encephalitis infections like Western Equine Encephalitis)

* Establishment of a statewide mosquito surveillance network

* Any person, animal, or bird suspected of having West Nile virus or other viruses carried by mosquitoes must have appropriate laboratory testing.

On August 1, 2001, the USDA and Fort Dodge Animal Health announced the approval of an inactivated vaccine against WNV for use in horses. Talk with your veterinarian; decide together if WNV vaccine would be appropriated for your horse.

More information and updates can be obtained at Or call the Washington State Department of Health at (360) 236-3362 or 236-3060.

Warmest regards and good health to you, your families and animal companions through the holidays and New Year!

-- Frosty Franklin


Open Breed
Contents & Features

Baxter Black - Empty Places at the Christmas Table

Vet Corner -
West Nile Virus

Real Estate Section - Water Pipe Tips During Cold Weather

Equine Dentistry

Now You Can Teach Your
Horse New Tricks

Bridle Wise - Evaluate Your Horseís IQ

The Gallop Pole - Standard Head & Leg Markings

Youth of the Month - Jamie Holcomb

December 11, 2001 11:24 PM