West Nile Virus is a viral disease carried by birds and transmitted by mosquitoes to other animals. The greatest incidence of the disease appears to be in late summer and early fall, although the disease is new enough in the United States to not have an established pattern.
Is West Nile Virus contagious?
No. There is no horse-to-horse or horse-to-human transmission. The transmission occurs through the mosquito, i.e. A horse or human has to be bitten by a mosquito carrying the virus in order to contract the disease.
What are the symptoms?
The symptoms of the West Nile Virus disease are similar to other diseases affecting the central nervous system (i.e. elevated temperature, ataxia, reduced mentation, inappetence, and sometimes an inability to stand). In addition, horses affected with the virus may show some facial tremors.
Is there a treatment?
There are no specific treatments available for horses which target the virus. All treatments at this point are supportive, and have been somewhat successful.
In endemic areas most protocols are recommending vaccinating 2-4 times a year and to be effective, the vaccine must be given prior to exposure to the disease.
Initial vaccination requires two injections, 3-6 weeks apart. Horses that are not vaccinated twice at the appropriate intervals require the aforementioned 2- shot series.
We recommend vaccinating for the West Nile Virus in the spring as well as the fall. Horses traveling to high risk areas should be vaccinated at least 2 weeks prior to departure. Keep in mind the pattern of the disease is markedly different from year to year, therefore these recommendations may change.
Vaccination is the best prevention available with greater than 90% efficacy upon challenge, but it is not a guarantee. The other preventative measure is to reduce exposure to mosquitoes.