Important Facts About the West Nile Virus

A Plague in North America Threatens Both People and Horses

Apr 11, 2009

The mosquito's pesky whine signals an alarm not to be ignored, for this pest may carry a plague: malaria, dengue fever, yellow fever, or, most recently, West Nile virus.

In past years most of the U.S. could take some comfort in the prevalence of these diseases flourishing elsewhere such as Africa, Asia, Eastern Europe and Central and South America. In 1999, though, West Nile encephalitis, resident in Africa, Asia and Europe, struck in the U.S. 2002 saw the first case in Canada.

Spread by mosquitoes who feast on infected birds, West Nile encephalitis, caused by a virus, now proliferates nationwide, a horror especially for horses and humans. The U.S. Center for Disease Control (CDC) reports 1,338 human cases of West Nile with 43 fatalities in the U.S. in 2008.

West Nile Symptoms

West Nile attacks the central nervous system. The clinical symptoms in horses may appear in various combinations of fever, listlessness, paralysis or weakness in the hind legs, hyper excitability, aimless walking, drooping lower lip, circling, head pressing, inability to swallow, convulsions and coma.

Although symptoms could be mild or missed in some cases, West Nile is often fatal. Annual equine inoculations against the disease are not 100 percent effective, but they are better than nothing, so long as the shots themselves do not adversely affect the horse in some way.

Currently West Nile inoculations are contraindicated for pregnant mares according to some expert opinions. Others feel the risk is worth the protection afforded by inoculations.

In people the symptoms are similar: e.g., fever, paralysis, neck stiffness, stupor, numbness, skin rash, swollen lymph glands, muscle weakness and convulsions.

The CDC estimates that one in 150 people who become infected will manifest serious symptoms. For those who do, the prognosis is not encouraging.

Neither is it for horses. So far there is no cure for an infected horse. Except for supportive treatment of the symptoms, the horse will either survive or not on its own. Treatment for serious cases in humans is not much better.

Preventive Measures

Combating the West Nile virus means primarily combating mosquitoes. Many communities undertake wholesale spraying of high risk areas, such as swamps where standing water invites mosquito populations to flourish. Battling the mosquito in this fashion while maintaining broader ecological integrity is no easy balancing act.

Poisons that kill mosquitoes are not necessarily discriminating about what or whom else they affect, such as the water supply, animals, and benign or even desirable insects. Then there are the unknown future effects to humans and the environment such poisons bring as carcinogens, immune suppressors and allergens.

Less “poisonous” measures are regular removal of standing water sources, cleaning gutters, and keeping animal water troughs emptied, cleaned and refilled with fresh water. These practices require vigilance and habit. Mosquitoes also like to make their home in discarded tires.

Another safety measure is to not touch a dead bird and remove it safely for disposal. Dead birds should be presumed infected by West Nile. The local health department may want dead birds reported for collection and testing. Birds are also mosquito predators, though. Natural combaters of mosquitoes are resident bird and bat populations. Preserving their habitat is a smart practice.

To ward off mosquitoes, the CDC recommends using a mosquito repellant containing DEET or Picaridin. Oil of Lemon Eucalyptus PMD and IR3535, called biopesticide repellants, are also effective. A Vermont company called Insect Control Systems, Inc. (insectcontrolsystems.net), has developed an effective natural insect killer derived from chyrsanthemums for spraying in barns. Carefully burning smudge pots that give off repellant vapors can be helpful in outdoor areas where people will be congregating.

Staying inside is the most fool-proof method of protection. Many stables keep horses in at night during the height of seasonal mosquito activity (twilight and night time), or if turned out, treated with repellant.

The copyright of the article Important Facts About the West Nile Virus in Horse Care is owned by Linda Ashar. Permission to republish Important Facts About the West Nile Virus in print or online must be granted by the author in writing.