West Nile Virus In Horses

West Nile virus (WNV) is a viral disease previously seen only in Africa, Asia, and southern Europe. This virus can cause encephalitis, an infection of the brain and the spinal cord. The West Nile virus is spread to people by the bite of an infected mosquito. The principal transmitter of West Nile virus is the Northern House Mosquito (Culex pipiens). Mosquitoes first become exposed to the virus when they feed on birds that are infected with WNV. Once the mosquito is infected, it may transmit the virus to people or other animals when it bites them. Many birds can be infected with the virus, but crows and blue jays are most likely to die from the infection. Horses, too, are prone to severe WNV infection. People cannot get WNV from another person or horse that has the disease.

How Could A Horse Get West Nile Virus?

Horses become infected with West Nile virus after being bitten by an infected mosquito. There is no evidence that horses can transmit West Nile virus to other horses, birds, or people.

What Are the Signs and Symptoms of West Nile Encephalitis in Horses?

In horses that do become clinically ill, the virus infects the central nervous system and causes symptoms of encephalitis. Clinical signs of encephalitis in horses include loss of appetite and depression, in addition to any combination of the following signs fever, weakness or paralysis of hind limbs, muscle fasciculations or muzzle twitching, impaired vision, ataxia (incoordination), head pressing, aimless wandering, convulsions, inability to swallow, circling, hyperexcitability, or coma.

It is important to note that not all horses with clinical signs of encephalitis have West Nile encephalitis.

Other diseases, including rabies, botulism, equine protozoal myeloencephalitis (EPM), and other mosquito-borne viral encephalitic diseases of horses caused by Eastern, Western, and Venezuelan encephalitis viruses, can cause a horse to have symptoms similar to WNV.

Is There Treatment For West Nile Encephalitis In Horses?

Currently, there is no specific treatment for West Nile encephalitis in horses. Supportive veterinary care is recommended.

Is There A Vaccine To Protect My Horse?

Currently, there is a new vaccine available against West Nile virus. It is imperative that horses are vaccinated twice initially, three to six weeks apart, with this vaccine. Horses vaccinated against Eastern, Western, and Venezuelan equine encephalitis are not protected against West Nile virus.

How Can I Prevent Mosquitoes From Affecting My Horses?

You can take some easy steps to prevent mosquitoes from affecting your horses:

• House horses indoors during peak periods of mosquito activity (dusk and dawn).
• Avoid turning on lights inside the stable during the evening and overnight. Mosquitoes are attracted to lights.
• Place incandescent bulbs around the perimeter of the stable to attract mosquitoes away from the horses. Black lights do not attract mosquitoes well.
• Remove all birds, including chickens, that are in or close to the stable.
• Look around the property periodically for dead birds, such as crows. Any dead birds should be reported to the local health department. Use gloves to handle dead birds or use an implement, such as a shovel.
• Eliminate areas of standing water on your property. Shallow standing water, used tires, manure storage pits, and drainage areas with stagnant water are ideal mosquito breeding places.
• Topical preparations containing mosquito repellents are available for horses. Read the product label before using and follow all instructions.
• Use fans on horses while in the stable to help deter mosquitoes.
• Fog stable premises with a pesticide in the evening to reduce mosquitoes. Read directions carefully before using.

For help in assessing mosquito exposure risks on your property and for suggested control practices, please contact your county Extension office, county Department of Environmental Protection, local Department of Health, local veterinarian, or mosquito and pest control company.

How Can I Reduce The Number Of Mosquitoes Around My Home?

You can reduce the number of mosquitoes around your home and neighborhood by reducing the amount of standing water available for mosquito breeding. Here are some simple steps you can take:

• Dispose of tin cans, plastic containers, ceramic pots, or similar water-holding containers on your property.
• Pay special attention to discarded tires. That is where lots of mosquitoes breed.
• Clean clogged roof gutters every year, particularly if the leaves from surrounding trees have a tendency to plug up the drains. Millions of mosquitoes can breed in roof gutters each season.
• Turn over plastic wading pools when not in use. A wading pool becomes a place for mosquitoes to breed.
• Turn over wheelbarrows and do not let water stagnate in birdbaths. Both provide breeding habitats for domestic mosquitoes.
• Aerate ornamental pools or stock them with fish. Water gardens can become major mosquito producers if they are allowed to stagnate.
• Clean and chlorinate swimming pools when not in use. A swimming pool left untended by a family on vacation for a month can produce enough mosquitoes to infest an entire neighborhood. Mosquitoes may even breed in the water that collects on pool covers.
• Use landscaping to eliminate standing water that collects on your property. Mosquitoes may breed in any puddle that lasts for more than four days.
• Make sure that doors and windows have tight-fitting screens. Repair or replace screens that have tears or holes in them.
• Stock permanent ponds or fountains with fish that eat mosquito larvae.
• Check around faucets and air conditioner units and repair leaks, eliminating puddles that remain for several days.

Can A Horse With West Nile Virus Infect Other Horses?

No. There is no documented evidence that West Nile virus is transmitted from horse to horse. However, if at all possible, horses with suspected West Nile virus should be isolated from mosquitoes and tested for the virus.

What Is the Incubation Period?

The incubation period of a West Nile virus infection is usually five to 15 days.

Do Birds Infected With The Virus Die Or Become Ill?

Large numbers of North American crows and other birds have died of West Nile virus infection.

What About Ticks?

Some ticks in Europe and Asia have been found to be infected with the virus. Therefore, infected ticks could prove to be a carrier and transmitter of the virus in the future. The U.S. Centers for Disease Control and Prevention also tested ticks in the 1999 outbreak area, but none were infected.

Source:

Ohio State University