Equine Health

Medicine & Husbandry

West Nile (WNV)

West Nile Virus (WNV), a sometimes fatal disease that affects both horses and people, has spread to over a dozen states in just two years.  This disease is carried by wild birds and transmitted by mosquitoes. The virus can cause encephalitis (inflammation of the brain) in horses causing stumbling, weakness of the hind end, paralysis, muscle twitching, and death. Treatment of the disease is intensive and costly with a prolonged and uncertain recovery.

Due to the rapid spread of this virus, the USDA and CDC recommend that horses be vaccinated for this disease. The vaccine consists of two injections given three to six weeks apart followed by annual boosters. If you have any questions or concerns about West Nile Virus vaccination or for a vaccination appointment please call the office.  For more updated information, visit www.equinewestnile.com.

Pest management is one of the critical preventative measures that owners can take to protect their horses against West Nile Virus (WNV) infection. The fewer mosquitoes that your horse comes in contact with the lower the odds of a bite from an infected one.  Average fly sprays applied topically are not usually effective against mosquitoes.  Face masks, fly sheets, and leg covers do help lower the body surface available for a bite, but leave the belly and other areas exposed.  Usually controlling the environment is easier and more effective.  Adult mosquitoes rest in weeds, so trim weeds around barns and houses and keep lawns mowed.  Reduce mosquito sources by eliminating breeding sites.  Mosquito larvae need standing water to complete their life-cycle.  Anything that traps water, such as old buckets, troughs, and standing water in pastures, should be drained.  For water that cannot be drained, microbial larvicides or “mosquito dunks” (sold at some hardware stores) can be applied to the water.  Insect growth regulators, which are synthetic chemicals, come as liquids, pellets, or granules and prevent larvae from emerging as adults.  Adulticides can also be used, but must be handled carefully as they are potentially toxic to other animals and insects.  These are usually applied from the ground or by aircraft as mists, fogs, or granules in severely infested areas.

As of September 2006 there have been 4,500 equine cases of WNV in the United States.  The vaccine available from Fort Dodge Animal Health should receive full approval from the federal government and will play a key role in the protection against this disease.  However, proper management and mosquito control are just as critical to reducing both horse and human exposure to this disease.

Yes, West Nile Virus (WNV) is in California again.   At the time this article was written, there were confirmed cases of human and equine WNV in several  California counties with multiple cases of equine deaths from the disease.  If your horse has been vaccinated and boostered for WNV, and the booster was within the last 6 months, your horse is fully vaccinated and should be protected.  If your horse’s last booster was later than 6 months ago, you should get another booster at this point.  If your horse has not been vaccinated, it is imperative that you do so immediately. It takes approximately 21 days after the last booster to confer total protection, so if you start your vaccination program now, it will be about two months before they are fully protected.  Another important aspect of prevention is mosquito control.  Any standing and stagnant water should be eliminated.  Insect repellent should be used at all times.  If you have mosquito larvae, a larvicide should be used.

Hotter weather in our area signals the end of rain and the emergence of disease causing insects.  Researchers at UC Davis are expecting human and equine infections and casualties from West Nile Virus (WNV).  “California will undoubtedly become affected this summer, so horsemen need to heed the lessons learned by the experience of other sates and properly prepare themselves now” said Greg Ferraro DVM, director of the UC Davis Center for Equine Health (CEH).  Recommendations on preparing for this disease include a proper vaccination schedule.  Veterinarians at CEH recommend that when the first West Nile cases are confirmed in California, all horses that haven’t been vaccinated in the  last six to eight weeks should be boostered. After that boosters should be administered every 6 months to adult horses (except for horses that have never had the vaccine– they will need to be boostered in three weeks).  Foals born to unvaccinated mares should be given their first shot at three months.  Foals born to mares which were boostered within two months of foaling should receive a first shot at four to six months. All foals should have three initial doses of the vaccine.  Fly hoods and bug spray also help keep insects away from horses.  Implementing environmental control by draining all standing water and other potential breeding sites for mosquitoes is also important.  Further information on California’s plans for combating WNV can be found at www.vetmed.ucdavis.edu/ceh/wnv_info.html.

For continued information, please see these websites.  They are updated daily and have all the current information that you will need to monitor the disease: www.westnile.ca.gov and www.vetmed.ucdavis.edu/ceh/wnv.   If you have any specific questions about your horse and this disease, please contact us.