West Nile Virus (WNV) is primarily transmitted between birds by mosquitoes, but can occasionally cause disease In horses exposed to infected mosquitoes. Experimental studies have concluded that horses are a dead-end host for West Nile Virus, so an infected horse is not a threat to other horses or people in contact with it. Infection does not always cause clinical disease in horses. However, when the virus does cause clinical symptoms in the horse, it can be very serious. Clinical signs are widely variable. Some horses may appear depressed or listless.Some exhibit flu-like symptoms including fever which may resolve then reappear a week later (biphasic). In more severe cases, horses may develop neurological signs ranging from muscular fasciculation (twitching), ataxia or wobbly drunken-like gait (especially progressive hind limb incoordination), circling, behavioral changes and in the most extreme cases, convulsions, coma and death. Approximately half of all horses that show more severe neurological signs, recover.

At this lime, there is no vaccination for West Nile Virus. However, stopping the bird-mosquito Infection cycle with vector control is the key to protecting horses. The type of mosquito primarily responsible for West Nile Virus transmission is the Culex app which spends its entire life within a range of about 1,000 yards of its breeding site. Local control of mosquito breeding therefore can be very effective in stopping transmission of this virus. Culex mosquitoes can breed in any stagnant water (puddles, water troughs, discarded tires, birdbaths, stagnant water in manure collection areas, pails, wheelbarrows, gutters, etc.). By reducing the number of breeding areas on and adjacent to your property, you can significantly reduce your horse's exposure to these insects.

Further recommendations for West Nile Virus control include:

1. Indoor stabling of horses from dusk to dawn. These are the feeding times for the female mosquitoes. Male mosquitoes do not bite horses.

2. Consider the use of insecticide sprays and repellents as recommended by your veterinarian.

3. Fly sheets. These may be used when horses are turned out.

The LIVMA recommends vaccinating your horse twice yearly for Eastern, and Western encephalitis (EEE/WEE). Because the vaccine protection is short-lived, two vaccinations, one in the spring before the mosquito season and a second six months later, will ensure your horse's protection throughout the year, Additional vaccinations are recommended against Rhinopneumonitis and Rabies. The chance of exposure to these diseases represent a greater threat than WNV.

Updated information on West Nile Virus can be found at the following web sites:

USDA www.aphis.usda.gov/vs/ep/WNV

New York State www.health.state.ny.us

Suffolk County www.co.suffolk.ny.us/health

For Information on pesticides used for mosquito control:

EPA www.epa.gov/pesticides/factsheets/skeeters.htm

You may contact the LIVMA at 516-756-1919