By Kristen Tribe

Since West Nile was first discovered in the United States in 1999, it has spread to 18 states, including Louisiana, halfway between New Orleans and the Texas border.

"It’s spreading through this country because it’s carried by migratory birds and spread by mosquitoes. Certainly, there’s some concern but it’s by no means a panic situation," says Dr. John Irby, Area 4 director, Texas Animal Health Commission.

West Nile Virus is very similar to eastern equine encephalomyelitis (EEE) and western equine encephalomyelitis (WEE), more commonly known as "sleeping sickness." All three of these viruses cause encephalitis (inflammation of the brain) and share the same method of transmission. Venezuelan equine encephalomyelitis also falls into this same category, but it has not been diagnosed in the United States since the early 1970s.

Although West Nile is a new threat to U.S. equine health, it doesn’t pose any greater threat than EEE or WEE at this time.

From Jan. 1, 2001, to Oct. 31, 2001, there were 347 confirmed cases of West Nile Virus infection in horses. As of late October, an outcome had been reported on 262 of those horses, 59 of which had died or were euthanized. The other 85 horses probably recovered without complications.

The infected horses were in Alabama, Connecticut, Delaware, Florida, Georgia, Illinois, Kentucky, Louisiana, Maryland, Massachusetts, Mississippi, New Jersey, New York, North Carolina, Pennsylvania, Rhode Island, Tennessee and Virginia.

In Texas, there were no cases of West Nile, but six cases of EEE and one case of WEE reported to the Texas Veterinary Medical Diagnostic Laboratory.

"There are certainly more cases of eastern and western reported nationally each year than West Nile, and I don’t know that the mortality rates are any higher for West Nile than it would be for eastern or western," Irby says.

Irby explains that extremely young or old horses are at the greatest risk of dying from West Nile because they may not have a strong immune system. Symptoms can range from animals staggering and running a fever to being so mild they’re almost unnoticeable. Irby says clinical signs of the disease could even show up one day and be gone the next.

"In my opinion, vaccination for West Nile should be incorporated in an annual immunization program for horses, which includes vaccinations for eastern and western encephalitis, strangles and equine influenza, depending on where you live," says Irby. "Until West Nile Virus is reported in Texas, it may be more important to vaccinate those horses being hauled regularly to events in affected states."

Fort Dodge has a conditionally licensed vaccine available through veterinarians. Treatment requires two intramuscular doses given three to six weeks apart. The product is believed to be effective with no bad side affects, but it could make your horses test positive for the disease.

Although West Nile is spreading to numerous states, USDA experts say the exposure of an individual horse is still considered a chance occurrence.

"A positive horse is just an indication that there are positive birds and active mosquitoes in the area," says Irby. Horses are considered dead end hosts and cannot transmit the virus to humans or other animals.

Mosquitoes acquire the virus from infected birds, and then they can transmit it to horses and even humans. Humans can also contract EEE and WEE from mosquitoes, and Dr. Joe Garrett, an epidemiologist with the Texas Department of Health, says human symptoms for all of these are almost indistinguishable.

"If you have a mild infection you might have a low fever and headache – almost a flu-like illness. If it’s severe you might have a high fever and stiff neck or become disoriented," he says. Shaking and convulsions can lead to paralysis or a coma, but he explains that such a severe case is rare.

Most people don’t even become ill. A mosquito can put the encephalitis virus into your body, and if you’re healthy, your body will take care of it. Those with a weakened immune system are at the greatest risk.

At the end of October, one case of human encephalitis had been reported in the state of Texas. Unlike horses, there is no vaccine available for humans.

In an effort to protect yourself and horses from West Nile and similar diseases, you should make an effort to control the mosquito population around your house and barns.

The U.S. Department of Agriculture gives the following recommendations:

• Reduce the population of mosquitoes, especially those involved in bird-to-bird transmission. This can help reduce or eliminate the presence of the virus in your area.
• Remove all man-made sources of stagnant water in which mosquitoes might breed.
• Dispose of any water-holding containers, including discarded tires.
• Drill holes in the bottom of containers that are left outdoors.
• Clean clogged roof gutters annually.
• Turn over plastic wading pools or wheelbarrows when not in use and do not allow water to stagnate in birdbaths.
• Aerate ornamental pools that are not in use and be aware that mosquitoes can breed in water that collects on swimming pool covers.
• Thoroughly clean livestock watering troughs monthly.

Garrett also recommends that you wear long sleeves, avoid activities during the major mosquito feeding times – early in the morning and late in the evening – and use a repellant containing deet. Irby suggests getting rid of any bird roosting areas, too.

Although West Nile Virus has only been in the United States for three years, producers have already been treating their horses for similar diseases, EEE and WEE. Prevention, symptoms and treatment should be a familiar routine, and even though it’s inevitable West Nile will hit Texas, there’s no reason for alarm.

An additional vaccination for West Nile and efforts to control the mosquito population are positive steps to protecting you and your horses.