August 2, 2006
Officials Confirm Death of Horse Due to West Nile
State officials Wednesday confirmed the first case of West Nile virus in Montana this year in a horse from Flathead County that died of the disease July 22.
The 2-year-old Quarterhorse stallion had not been vaccinated, according to Dr. Jeanne Rankin, assistant state veterinarian with the Montana Department of Livestock (DOL).
“We highly recommend that horse owners get their animals vaccinated against West Nile,” Dr. Rankin said. “There are USDA licensed vaccines available, and horses should initially get two doses three to six weeks apart. They also should get an annual booster.”
The cause of the Flathead County horse’s death was confirmed July 27 at the state Veterinary Diagnostic Laboratory in Bozeman. It marked the first evidence this summer that West Nile virus is still active in Montana.
WNV is carried primarily by birds but can be transmitted by mosquitoes to humans, horses, and some other animals. The first documented case of the disease in the United States occurred in New York in 1999, and it has since spread westward into nearly every state.
In Montana, the first confirmed case of the disease was found in a horse in 2002. Since then, the state has had a total of 262 confirmed cases of WNV in humans, resulting in four deaths, and 349 cases in horses, with 98 deaths.
WNV does not appear to spread from horse to horse or from person to person.
Many infected horses and humans do not develop any illness, but among horses that become ill, about a third die or need to be euthanized, Dr. Rankin said.
In humans, about 80 percent of those infected notice no symptoms and develop immunity, according to Elton Mosher, disease surveillance specialist with the Montana Department of Public Health and Human Services (DPHHS). About 20 percent experience a mild flu-like illness called West Nile fever, which may last for three to six days. Generally, no treatment is needed.
Fewer than 1 out of 150 infected people may be come severely infected with West Nile encephalitis or West Nile meningitis, Mosher said. Symptoms of this disease may include headache, rash, high fever, stiff neck, mental confusion, muscle weakness, tremors, convulsions, coma and paralysis. People over the age of 50 appear to be at greatest risk of serious illness.
There is not yet a vaccine to protect humans from WNV. Individuals who develop any of the symptoms should see their health-care provider, Mosher said.
In many states, the number of West Nile cases has gradually declined over time as people and animals develop immunity from infection. Whether Montana has seen the worst of WNV is difficult to predict, state health officials say.
“We continue to monitor this disease, and we continue to encourage people to take precautions to avoid it, which means basically trying to avoid getting bitten by mosquitoes,” Mosher said.
Precautions include:
- Staying indoors as much as possible during the early morning and evening hours, when mosquitoes are most active. If possible, horses should be stabled at dusk and dawn.
- Wearing long sleeves and pants when you must be outdoors and mosquitoes are active.
- Applying an insect repellent containing 25-35 percent DEET before going outdoors. Children ages 2-12 should use repellent with 10 percent DEET or less. Products containing picaridin and permethrin have also been found to be effective in repelling mosquitoes, as has oil of lemon eucalyptus.
- Draining standing water from old tires, barrels, buckets, clogged rain gutters, and other items, and changing water in pet bowls, flowerpots, and birdbaths at least twice a week.
Dr. Rankin noted that livestock watering troughs should be cleaned thoroughly and regularly.
“Another good solution is to use a product called BTI Dunks, which is available at garden shops,” she said. “It contains natural bacteria that, when put into the water, will kill fly and mosquito larvae, but it’s nontoxic to animals.”
More information about WNV is available under Featured Topics on the DPHHS Web site at: www.dphhs.mt.gov. More information about the disease in horses is available from the Department of Livestock Web site at www.mt.gov/liv.
Page last updated: 08/03/2006
