As if there wasn't enough for horse owners to worry about with the likes of mountain lions lurking in their animals' midst, the season for the spread of West Nile virus is fast approaching.
The North Dakota Veterinary Diagnostic Laboratory tested 39 horses for the infection last year. Of the samples submitted, 14 cases, or 36 percent, tested positive for West Nile virus from 11 counties, including one sample each from Grant, McKenzie and Stark counties, according to the North Dakota Department of Health.
Horse owners should be on the lookout for signs and symptoms that could indicate the virus has struck.
"Of domesticated livestock and companion animals, horses are the most susceptible to West Nile virus," says Charles L. Stoltenow, veterinarian and professor with the North Dakota State University Extension Animal Systems Program. "I'm not quite sure why, but horses are also affected by eastern Equine Encephalitis. West Nile virus can infect other types of livestock, but clinical cases seem rare in those animals."
Beth Carlson, deputy state veterinarian, says North Dakota has also had a small number of dogs affected by the virus, but horses suffer the brunt of the disease.
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"It is possible that they are more susceptible, but it is also theorized that because they have thinner skin than other livestock, such as cattle, it is easier for mosquitoes to bite and spread the virus to them," she says.
Of the West Nile virus cases found in North Dakota horses, which most likely developed from mosquito bites in the same way humans contract the disease, about 40 percent of the cases result in the death of the horse, according to the North Dakota Department of Agriculture.
Infected horses will be lethargic, have problems with coordination and weak limbs, partial paralysis and may die.
"Animals that may be affected should be under the care of a veterinarian," Carlson says. "Supportive treatment is very important and may include fluid therapy, anti-inflammatories and other therapies. I would recommend visiting with a practicing veterinarian for specific treatment options."
Outbreaks of the virus in horses occurred in the U.S. from 1999 to 2002, according to the Centers for Disease Control and Prevention.
While cases of West Nile virus in equines run the risk of turning fatal, the NDDA found that under many circumstances, when the virus is found in equines, the animal does not need to be euthanized and most horses can recover from the disease.
To protect horses from mosquito bites, the NDDA recommends owners insect-proof stables with repellant that contains DEET, keep horses indoors during peak times for mosquitoes, avoid areas mosquitoes are known to inhabit -- such as sloughs and heavily forested areas -- vaccinate animals and use fans to reduce ability of mosquitoes to make contact with horses.
The NDDA also advises people to throw away containers that can collect water and to make sure livestock water sources are cleaned thoroughly on a monthly basis.
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Summer and fall months have the highest incidence of West Nile virus in horses.
"All animals benefit from limiting their exposure to mosquitoes, whether that means eliminating standing water, spraying the environment, using a repellant on the animal, or keeping the animal indoors during peak mosquito activity times, if possible," Carlson says.
Prevention
The best means of protecting horses, Stoltenow says, is to prevent them from contracting the virus in the first place through an annual West Nile virus vaccination, which is not an option for humans.
Erika Schumacher, a veterinarian at West Dakota Vet Clinic in Dickinson, says it's recommended that owners start getting their horses vaccinated in late April or early May, before the peak season for cases of West Nile virus in horses in late July through October.
Schumacher understands the importance of the vaccination after four of her family's horses came down with the virus more than 10 years ago.
Two of the horses died.
"We were able to keep the other two alive, although our veterinarian didn't quite know what he was treating until the blood work came back," she says. "The one horse ended up with laminitis in one foot, which is common with inflammation in horses."
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The vaccination remains the best means of protecting horses from West Nile virus.
Without it, there is little that can be done once the virus hits, Stoltenow says.
"Supportive care is the best you can do if a horse develops the West Nile virus," he says. "There is no magic cure."
