West Nile encephalitis:
Vaccination is the best defense against this mosquito-borne viral disease, which in just two decades has become a health threat for horses across the country.
Vaccination is the best defense against this mosquito-borne viral disease, which in just two decades has become a health threat for horses across the country.
hen warm spring weather brings out the mosquitoes, you’ll need to take measures to protect your horse against a number of diseases these pests can carry. One of these is West Nile encephalitis, although people typically refer to the disease by
the name of the virus that causes it: West Nile virus (WNV).
First identified in North America in 1999, WNV spread across the continent within just a few years, and now it remains a persistent threat. Horses (and people) become infected with WNV when bitten by infected mosquitoes, which pick up the virus from wild birds. Horses are considered dead-end hosts, meaning that they cannot pass the disease on to others.
Most horses who are infected with WNV show few, if any, signs of disease. Some might develop a low fever and weakness that passes quickly. In roughly 10 percent of infected horses, however, the virus crosses into the horse’s central nervous system and causes a more serious illness. Signs of the disease may include high fever, loss of appetite, depression, muscle twitching, stumbling or incoordination, weakness or paralysis, and recumbency.
There is no specific treatment for WNV beyond intravenous fluids, antiinflammatory medications and other supportive care. Recumbent horses may benefit from being supported in a sling. Neurological signs may begin to subside within five to seven days, although in some cases they may persist for
several weeks, and it may take up to a year for a horse to return to his previous level of work. Roughly onethird of horses who fall ill with WNV either die or are put down.
VACCINATION
By far the most effective way to protect your horse against WNV is to keep his vaccinations up to date. In fact, WNV is included on the list of “core vaccines” the American Association of Equine Practitioners recommends for the majority of horses.
Several vaccines are available, using both modified-live and killed virus formulations. Annual boosters, prior to the start of mosquito season, are recommended for previously vaccinated adult horses. Those who have never been vaccinated before will require a follow-up dose four to six weeks after the initial injection. Boosters may be needed at six-month intervals for very young and very old horses, as well as those who have compromised immune systems
By far the most effective way to protect your horse against WNV is to keep his vaccinations up to date.
and/or who live in areas with large populations of mosquitoes year-round.
Your veterinarian can suggest specific products and schedules that are appropriate for your horse.
OTHER PREVENTIVE MEASURES
Any steps you can take to reduce the populations of mosquitoes on your farm will reduce the risk of spreading disease to your horses as well as to people and other animals. For the most part, this means reducing or eliminating standing water where the mosquitoes lay their eggs:
• Dispose of old tires, unused buckets and other debris that can catch rainwater. Keep garbage cans covered, and prop wheelbarrows against a wall or turn them over when not in use. Make sure tarps placed over trailers, boats or other items are not collecting water in
their folds. Empty water troughs in unused fields and paddocks.
• Keep all gutters and drainage ditches unclogged and flowing freely. Gutter screens and other types of covers can help prevent fallen leaves from blocking the flow of water. Also make sure puddles are not forming under downspouts. If they are, consider installing downspout extensions or digging channels to keep water draining away from the foundation.
• Repair dripping faucets and spigots. Not only do drips waste water, but they can form persistent puddles.
• Change your animals’ drinking water regularly. Every few days, empty and change the water in buckets as well as drinking bowls for dogs and cats and birdbaths. Mosquito life cycles vary by species, but most take one to two weeks to reach maturity after hatching, so changing water in larger troughs once a week ought to reduce their numbers.
• Use larvicidal products when necessary. When standing water is difficult to change or remove entirely, such as in outdoor drain traps, or when draining and refilling troughs weekly isn’t a viable option, consider adding larvicidal products to the water. Many common products contain Bti--- Bacillus thuringiensis subspecies israelensis, a bacterium that produces toxins that kill mosquito larvae. According to the Environmental Protection Agency, Bti is not toxic to people and is approved for use in organic farming. Talk to your veterinarian for recommendations on specific products that are safe to use in water that your horses will drink.
• Keep natural waterways healthy. Fish and other predators will feed on larvae as well as adult mosquitoes in and around ponds, streams and other waterways. If natural ponds and streams on your property are producing too many mosquitoes, ask your local extension agent for advice on how to reduce stagnation and attract and retain beneficial species.
• Apply repellents. Read the label on your fly sprays to make sure they also work against mosquitoes, then apply as needed before turning horses out or trail riding.
• Place fans inside barns. Mosquitoes are not strong fliers. A few well-placed fans that keep the air moving through your stalls will prevent the pests from approaching and feeding on your horses.
Reduce or eliminate standing water where the mosquitoes lay their eggs.