August 8, 2002

Vaccinate Horses for West Nile Virus Now, NDSU Veterinarian Advises

North Dakota horse owners should have their horses vaccinated against the West Nile virus, says a North Dakota State University veterinarian.

"It’s clear that the disease is here in the state and will continue to be a threat in coming years, and there is no treatment for horses that contract the disease," says Charlie Stoltenow of the NDSU Extension Service. "Vaccinating your horses is their best bet for protection. There is still six weeks or more left of the mosquito season."

Stoltenow says horse owners should check with their local veterinarian to determine if the vaccine is available. "There is a big demand for the vaccine, so there may be some localized shortages." Stoltenow also recommends vaccinating animals against eastern equine encephalitis and western equine encephalitis if horses aren’t already protected.

The West Nile virus vaccine is a killed, whole cell vaccine for use in healthy horses. The first time horses are vaccinated they need two doses of vaccine separated by a period of three to six weeks. A booster dose is needed every year. Horses aren’t fully protected until three to four weeks after the second dose.

Vaccine labels indicate that horses are able to receive the vaccine as early as six months of age. Depending on the situation, veterinarians may be able to vaccinate younger foals.

The vaccine is available under a conditional license, which means it has not been fully tested. "Preliminary data indicates the vaccine is very effective and very safe," Stoltenow says.

In horses, the disease can cause acute, fatal neurologic disease affecting the brain and spinal cord. However, clinical disease does not always occur. Horses may show signs of stumbling, weakness and rear limb incoordination. Mildly affected horses can recover in two to seven days.

Horses that survive appear to recover fully. The disease can be diagnosed through a blood sample.

"Rabies should always be considered when horses show signs of nervous system disease," Stoltenow says. "Approach those animals cautiously and take measures to protect yourself from exposure."

The West Nile virus is spread by the bite of an infected mosquito only, and even in areas where the disease is known to exist, less than 1 percent of mosquitoes are infected and less than 1 percent of people bitten by an infected mosquito become infected, he says.

Stoltenow says that in addition to having horses vaccinated, horse owners should take steps to limit their horses’ exposure to mosquitoes. Remove water-holding containers. Clean clogged roof gutters. Turn over plastic wading pools or wheel barrows. Change water frequently in birdbaths, ornamental pools and stock tanks. Add screens to stables and use insect repellants containing DEET. Keep animals inside during sunset and dawn which, are peak mosquito feeding hours. Avoid swamps and heavily forested areas where mosquitoes are more numerous. Fans in stables may disrupt mosquitoes.

For more information on the West Nile virus and horses visit the North Dakota Department of Agriculture Web site at www.agdepartment.com or the U.S. Department of Agriculture Web site at www.aphis.usda.gov/oa/wnv/.

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Source: Charlie Stoltenow, (701) 231-7522, cstolten@ndsuext.nodak.edu
Editor: Tom Jirik, (701) 231-9629, tjirik@ndsuext.nodak.edu