Equine West Nile vaccines effective; Humans still waiting

Wednesday, July 13, 2005

The Oklahoma State University veterinarian who diagnosed the first West Nile virus cases in Oklahoma this year said its occurrence in horses in the state appears to be in decline because of the proliferation of vaccinations. An inoculation for humans, however, remains under development.

The confirmation July 7 of two horses in Comanche and Washita counties testing positive for the virus was the result of evaluations conducted on June 23 and June 28 by Dr. Jeremiah T. Saliki, a virologist at the Oklahoma Animal Disease Diagnostic Laboratory, a unit of the OSU Center for Veterinary Health Sciences.

Saliki and his staff analyzed blood samples submitted by two veterinarians who suspected the virus upon observing animals that demonstrated its clinical symptoms, such as staggering on the hind legs, uncontrollable muscle twitching and other central nervous system disorders.

Saliki said since the West Nile virus was first observed in Oklahoma in 2002, veterinarians have seen progressively smaller numbers of infected horses, and those that demonstrate its clinical symptoms often suffer less severely. He attributes both to widespread vaccinations that currently boast a rate of protection effectiveness approaching 94%.

No specific, equine treatment exists for the West Nile virus, Saliki said, but approximately 80% of horses that demonstrate its clinical symptoms and receive care return to normal, for the most part. Owners are strongly encouraged to get their horses vaccinated. 

A few facts about the West Nile virus:

• Receptors possessed by humans, horses and many bird species allow them to be infected by the virus and determine their levels of susceptibility.
• The only way to contract the virus is to be bitten by a mosquito.
• The virus is spread almost entirely by mosquitoes that have bitten an infected bird.
• Transmission by a mosquito that has bitten an infected horse or human is unlikely because humans and horses are dead-end hosts.
• The virus cannot be contracted by interaction with infected humans or horses since they are dead-end hosts.
• To avoid infection, avoid mosquito bites.

Tips include:

• Do not allow water to stand and stagnate around the house, e.g., in old tires. And aerate pools and ponds.
• If possible, avoid going outdoors at dawn and dusk when mosquitoes are most active.
• Apply insect repellant and wear long pants and long sleeves.

For more information, reporters can contact Saliki at OSU CVHS at 405-744-6623.