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West Nile Virus is a Threat to Unvaccinated Horses


As spring approaches and temperatures rise, growing mosquito populations will increase the risk for deadly mosquito-borne diseases, including West Nile virus and equine encephalomyelitis (Sleeping Sickness).

Since its discovery in the United States in 1999, West Nile virus has spread rapidly across the country and poses a significant health threat to humans, horses and other animals.

“The North American West Nile virus epidemic persists,” says Lyle Peterson, MD, MPH, Director of Vector-Borne Infectious Diseases for the Federal Centers for Disease Control and Prevention, addressing the seventh National Conference on West Nile Virus in the United States.

Unseasonably warm weather and mild winter conditions, which have been experienced in many parts of the country this year, may lead to an increased threat of West Nile virus. Torrential rains in other parts of the United States further complicate the risk.

West Nile was found in mosquitoes in January in Baton Rouge, La. In California, four counties have already reported birds testing positive for the disease, a finding that is “early in the season,” according to Gary Erbeck, Director of the San Diego County Department of Environmental Health.

Randy Phillips, who is helping to coordinate the West Nile virus response at the Clark County Health Department in Vancouver, Wash., says there’s an increased chance of West Nile in northern Oregon and Southwest Washington. “Mosquitoes may be more prevalent due to the high rains and mild temperatures we’ve had this year,” says Phillips.

Guidelines from the American Association of Equine Practitioners (AAEP) state proper vaccination of previously non-vaccinated horses involves administration of two doses of vaccine three to six weeks apart. Once the first series of vaccinations are complete, horses should be vaccinated semi-annually or more frequently, depending on the geographical risk. Annual revaccination is best completed in the spring, prior to the onset of mosquito season. Horse owners should contact their veterinarian as soon as possible to evaluate threat levels in the area and determine their horse’s current vaccination status, to ensure they will have maximum protection against disease.

Limiting exposure to mosquitoes is fundamental in helping prevent the spread of West Nile virus and Sleeping Sickness. According to the USDA, the following precautions may help reduce the risk of West Nile around homes and stables:

• Keep horses stables during dawn and dusk when mosquitoes are most active.
• Turn off lights that attract mosquitoes.
• Use fluorescent lights, which do not attract mosquitoes.
• Keep screens in stable windows.
• Make sure roof gutters drain properly.
• Turn over plastic wading pools and wheelbarrows when not in use.
• Empty water collecting in buckets, tarps, pool covers and tires.
• Clean water troughs and birdbaths at least once a week.
• Use mosquito repellent.

Early season mosquito control, in particular, can interfere with the life cycle of mosquitoes that feed on infected birds. And by controlling mosquitoes early in the season, spring and summer populations will be reduced.

Spring and Fall Wellness Exams Help Horses Stay Healthy Year Round

Nearly every horse owner has experienced an equine medical emergency. Certain kinds of colic, lameness, some foaling conditions and nearly all common equine diseases are examples of “potential” emergencies. Many crises, however, can be prevented with twice-a-year wellness exams, routine vaccinations and year round parasite control.

Semi-annual wellness exams allow a veterinarian to tailor season-specific vaccinations and parasite control treatments at the time of year when they are most beneficial. By scheduling exams in the spring and fall, horse owners also have the opportunity to consult with their veterinarian about nutrition, behavior, emerging disease threats in the area and other horse health issues.

“While there’s no way to completely eliminate emergency situations, a comprehensive health program, complete with spring and fall wellness exams, will minimize the chance of unexpected, life threatening and costly illness,” says Robert Magnus, DVM, founder and partner of the Wisconsin Equine Clinic and Hospital. “Wellness exams are the best way to detect, treat and, ideally, prevent health problems before they become serious or result in a prolonged setback.”

According to Dr. Magnus, whose clinic has offered a twice-a-year wellness exam program for the past six years, atypical equine wellness exam includes:

• Evaluation of the horse’s diet, level of activity, behavior and any changes since the last veterinary visit.
• Assessment of the horse’s overall conditioning.
• Analysis of posture and gait.
• Examination of hair coat and skin.
• Listening to the heartbeat, lungs and abdomen.
• Conducting as eye exam and dental exam.
• Administration of appropriate vaccinations.
• Recording vitals: pulse, temperature, respiratory rate and character.


According to the American Association of Equine Practitioners, the following situations are serious enough that a veterinarian should be called immediately:

• Any uncontrolled bleeding.
• Foreign objects protruding from the body (don’t remove them).
• Lacerations.
• Injury to the eye or eyelids.
• Aggressive or unusual behavior.
• Neurological signs (tripping, walking into objects).
• Lameness.
• Mares which are actively in labor for more than 20 minutes without progress.
• Difficulty breathing.
• Multiple animals getting sick at once.
• Off feed.
• Signs of abdominal discomfort (colic)


When in doubt, call a veterinarian. Keep your veterinarian’s phone number and your first aid kit handy. In an emergency, time is critical. By acting quickly and promptly, you can minimize the consequences of an injury or illness. Your horse’s health and well-being depend on it.

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