Fortunately, we have been lucky in the Pacific Northwest (especially here in Western Washington) not to have seen much West Nile Disease in horses.  It is all around us, however.  In fact, Idaho had 338 reported cases in horses in 2006, up from 114 in 2005 and 0 in 2003.  And these are just reported cases.  There are bound to be others that are not reported or not diagnosed.  Other surrounding states have had similar increases in West Nile Virus cases:

I say this so that horse owners might seriously think about starting or continuing to have West Nile Virus prevention as part of their core vaccination program, even if they haven’t seen the disease in their area.

As a review, West Nile Disease is a virus that was first detected in the U.S. in 1999 on the East Coast.  It quickly spread throughout the continental United States, and in 2003 it was detected in over 5100 horses in 48 states.  West Nile Virus (WNV) is spread across the country by migrating birds.  Mosquitoes pick up the virus and spread it to other birds, horses, people, and other animals, although horses and humans are particularly sensitive to the virus.  Horses and humans are dead-end hosts, meaning they cannot pass the virus to other horses or people.

The virus causes brain inflammation, or encephalitis.  Clinical signs in horses may include stumbling, incoordination, depression, apprehension, weakness, paralysis, muscle twitching, and death.  Fever may or may not be present.  Diagnosis is based on clinical signs and blood testing. Treatment is purely supportive and may include anti-inflammatory medications and intravenous fluids.  Unfortunately, 30% of unvaccinated horses that are infected with the virus will die.  Also, many recovered horses may end up with permanent damage.

Luckily, there are three vaccinations available for horses, all of which offer excellent protection from disease.  Fort Dodge’s West Nile Innovator, Merial’s Recombitek, and now Intervet’s PreveNile give horse owners plenty of choices for West Nile protection.  Discuss with your veterinarian which may be the best option for your situation. 

Also, timing of vaccination is crucial.  Most cases of West Nile Disease start in late July and August and peak in late October and November.  Vaccinating in the spring should give horses the best protection going into summer.

Mosquito control is also extremely important for controlling WNV, especially for humans, since there is no vaccine for us.  During summer and fall, standing/stagnant water should be removed because it is a breeding ground for mosquitoes.  Additionally, there are some insect control products for horses that are labeled for the control of mosquitoes as well as flies.

In conclusion, don’t forget about West Nile Virus.  It is in Washington and every state in the region.  This just might be the year it finally hits us.  The USDA/APHIS website (http://www.aphis.usda.gov/vs/nahss/equine/) has great information on WNV and monitors each state case incidence rate.