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Northwest Iowa Dairy Outlooks

A local discussion of current science and issues concerning dairying in northwest iowa

In 2015 West Nile virus (WNV) infected 40 horse in Texas, so far in 2016 only one case has been identified and that is in Limestone County, but it is early in the season.

West Nile virus is defined as zoonotic, which means it can be transferred between animals and humans.The virus is generally transmitted from birds by mosquitoes to horses and humans. For this reason, the virus is more common in the summer or fall when birds are migrating from the north. Horses and humans are considered to be dead-end hosts for the virus and are not directly contagious from horse to horse or horse to human.

Since the fatality rate for horses exhibiting clinical signs of WNV infection is over 30 percent, utilizing a vaccine is recommended.

All of the current West Nile vaccine products carry one year duration of immunity. Veterinarians recommend adult horses previously vaccinated, be vaccinated annually in the spring, prior to the onset of the insect vector season; but, the important issue is to get the horse vaccinated and then put it on a spring schedule.

“Vaccination has significantly decreased the incidence of West Nile disease in horses in the face of a steady increase of case numbers in humans, where there is no vaccine available,” says Dr. Leslie Easterwood, clinical assistant professor at the Texas A&M College of Veterinary Medicine & Biomedical Sciences. “Horses are recommended to be vaccinated twice yearly in areas of the country where mosquitos are present all year.”

For horses at high risk, the more frequent vaccination or appropriately timed revaccination is recommended in order to induce protective immunity during periods of likely exposure. For instance, juvenile horses less than five years of age, appear to be more susceptible than adult horses and geriatric horses have been demonstrated to have enhanced susceptibility to WNV disease.

Recovered horses likely develop life-long immunity, but this has not been confirmed. Consider revaccination if the immune status of the animal changes the risk for susceptibility to infection or at the recommendation of the attending veterinarian.

As a horse owner it is important to recognize the signs of the virus and to have a veterinarian ready to call. The sooner the symptoms are identified and the horse receives treatment, the better chance the horse has in surviving. According to Easterwood, one third of all equine West Nile cases generally survive with proper intervention.

“If an owner sees neurologic signs of wobbly stance, unsteady movement, depression, not eating, with or without muscle twitching, they should call their veterinarian right away,” explained Easterwood, even if the horse has been vaccinated.

Although the West Nile vaccine has proven effective, Easterwood reminds horse owners that no vaccine is 100 percent protective.

Additionally, horse owners should take steps to reduce the amount of mosquitos around their facilities by eliminating standing water; keeping stalls and pens clean; using equine mosquito repellents, fly sheets, and fly masks; plus placing fans inside stalls since mosquitos have difficulty flying in wind.


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