West Nile And Your Four-Legged Friends

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As Arizonans work to protect their families from the West Nile virus, veterinarians hope you don't forget to vaccinate your horse.

Arizona is leading the nation in human cases of West Nile this year, accounting for 247 of the 406 cases that have been reported to the Centers for Disease Control to date.

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Protecting your horse can be as simple as getting a vaccine from your veterinarian. Homeowners also should make sure that there is no standing water around the property, and be aware that peak mosquito hours are from dusk to dawn.

But humans are not the only animals susceptible to the disease, said Will Humble, bureau chief for the Arizona Department of Health Services. Horses and birds also can be infected.

This should be especially troubling to horse owners because West Nile is more dangerous for horses than humans, Humble said.

While the virus kills only one percent of humans who experience serious symptoms of the disease, West Nile proves fatal to 50 percent of horses that actually show signs of infection.

Horses that have been infected may begin to stagger, head press in their stalls, lie down and frequently twitch, said Danielle Hettler, veterinarian at the Star Valley Animal Clinic. Horse owners should take precautions against the disease by asking their veterinarians about West Nile vaccinations, she said.

Both the Fort Dodge and Merial vaccines have been approved to protect horses against West Nile. These vaccinations require two initial administrations and then a booster once a year, Hettler said.

While Arizona's West Nile outbreak has mostly been confined to Maricopa County -- there have not yet been any cases of West Nile reported in Gila County this year -- Payson residents should still be worried about the disease, Humble said.

"You have all the ingredients you need," he said. "It's probably just a matter of time."

The virus is passed when a mosquito bites an infected animal, usually a bird, and then passes the virus to the next animal it bites, Humble said.

"When West Nile virus gets going between birds and mosquitoes both, that's when you've got an epidemic," he said.

One of the best ways to protect humans and horses alike from West Nile is to make sure there are no sources of stagnant water in your neighborhood -- mosquitoes thrive and multiply in warm, wet areas, Humble said.

That includes standing water in horse troughs. Water supplies should be kept low and changed twice a week to discourage mosquitoes from lingering, Hettler said.

While a human vaccine is not yet available, people can guard themselves against mosquito bites by avoiding areas with mosquitoes at dawn or dusk, when the insects are most active, Humble said. If that is not possible, people should use insect repellent containing Deet to effectively ward off mosquitoes.

Fight the bite

Avoid Mosquito Bites: Apply Insect Repellent Containing DEET

(Look for: N,N-diethyl-meta-toluamide) to exposed skin when you go outdoors. Even a short time being outdoors can be long enough to get a mosquito bite.
Clothing Can Help Reduce Mosquito Bites

When possible, wear long-sleeves, long pants and socks when outdoors. Mosquitoes may bite through thin clothing, so spraying clothes with repellent containing permethrin or DEET will give extra protection. Don't apply repellents containing permethrin directly to skin. Do not spray repellent containing DEET on the skin under your clothing.

Be Aware of Peak Mosquito Hours

The hours from dusk to dawn are peak mosquito biting times for many species of mosquitoes. Take extra care to use repellent and protective clothing during evening and early morning -- or consider avoiding outdoor activities during these times.

Mosquito-Proof Your Home

Drain standing water from around your home

Mosquitoes lay their eggs in standing water. Limit the number of places around your home for mosquitoes to breed by getting rid of items that hold water.

Install or Repair Screens

Some mosquitoes like to come indoors. Keep them outside by having well-fitting screens on both windows and doors. Offer to help neighbors whose screens might be in bad shape.
Source: Centers for Disease Control

West Nile Virus and Horses

Q. Has West Nile virus caused severe illness or death in horses?

A. Yes, while data suggest that most horses infected with West Nile virus recover, results of investigations indicate that West Nile virus has caused deaths in horses in the United States.

Q. How do the horses become infected with West Nile virus?

A. The same way humans become infected--by the bite of infectious mosquitoes. The virus is located in the mosquito's salivary glands. Whenmosquitoes bite or "feed" on the horse, the virus is injected into its blood system. The virus then multiplies and may cause illness. The mosquitoes become infected when they feed on infected birds or other animals.

Q. How does the virus cause severe illness or death in horses?

A. Following transmission by an infected mosquito, West Nile virus multiplies in the horse's blood system, crosses the blood brain barrier, and infects the brain. The virus interferes with normal central nervous system functioning and causes inflammation of the brain.

Q. Can I get infected with West Nile virus by caring for an infected horse?

A. West Nile virus is transmitted by infectious mosquitoes. There is no documented evidence of person-to-person or animal-to-person transmission of West Nile virus. Normal veterinary infection control precautions should be followed when caring for a horse suspected to have this or any viral infection.

Q. Can a horse infected with West Nile virus infect horses in neighboring stalls?

A. No. There is no documented evidence that West Nile virus is transmitted between horses. However, horses with suspected West Nile virus should be isolated from mosquito bites, if at all possible.

Q. My horse is vaccinated against eastern equine encephalitis (EEE), western equine encephalitis (WEE), and Venezuelan equine encephalitis (VEE). Will these vaccines protect my horse against West Nile virus infection?

A. No. EEE, WEE, and VEE belong to another family of viruses for which there is no cross-protection.

Q. Can I vaccinate my horse against West Nile virus infection?

A. A West Nile virus vaccine for horses was recently approved, but its effectiveness is unknown.

Q. How long will a horse infected with West Nile virus be infectious?

A. We do not know if an infected horse can be infectious (i.e., cause mosquitoes feeding on it to become infected). However, previously published data suggest that the virus is detectable in the blood for only a few days.

Q. What is the treatment for a horse infected with West Nile virus? Should it be destroyed?

A. There is no reason to destroy a horse just because it has been infected with West Nile virus. Data suggest that most horses recover from the infection. Treatment would be supportive and consistent with standard veterinary practices for animals infected with a viral agent.

Source: Centers for Disease Control

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