West Nile Virus Q & A with Peter Timoney, FRCVS, PhD

Peter Timoney, FRCVS, PhD, is head of the Gluck Equine Research Center in Kentucky and one of the world's leading authorities on equine infectious disease.

Q: What is West Nile encephalitis?

Inflammation of the central nervous system (brain and spinal cord) caused by a mosquito-borne virus named West Nile virus. This virus was first identified as far back as 1935. Historically it is known to be distributed in Africa, the Middle East, and Southwest Asia. It has been introduced in sporadic occasions in various southern European countries. It has never been previously isolated or known to occur in the Americas.

Q: In what species can this virus cause illness?

Historically West Nile virus can cause illness and in some cases death in humans, horses, and certain species of birds.

Q: How do horses get West Nile virus?

Horses contract West Nile virus infection after being bitten by mosquitoes that are infected by the virus.

Q: How do the mosquitoes become infected with the virus?

The primary source for West Nile virus for various species of mosquitoes are different species of birds that are carrying the virus in their bloodstream when the mosquitoes feed upon them.

Q: Can horses pass West Nile virus to other horses, humans, or animals?

Under natural circumstances, there is no evidence that horses can act as a source of West Nile virus for other horses or humans or birds.

Q: What does West Nile virus do to a horse?

Following natural exposure to West Nile virus, many horses will develop subclinical or inapparent infection with the virus. in a small percentage of cases, the virus will invade the central nervous system of the infected horses and this can result in the development of signs of central nervous system disturbance of varying severity, which in some cases can be so severe as to result in the death of the affected animal.

Q: What is the treatment for West Nile encephalitis?

There is no specific anti-viral treatment for West Nile encephalitis in horses. Treatment of affected animals is symptomatic and aimed at lessening the severity of signs of central nervous system disturbance of the affected animal.

Q: Is there a vaccine against West Nile Virus?

Currently there is no vaccine available against West Nile virus. Routine vaccination of horses against Eastern and Western equine encephalitis will not confer protection against West Nile virus.

Q: What can owners do to protect horses?

The best precautions that owners can take to reduce the risk of horses being bitten by mosquitoes infected by West Nile virus would be to house those animals during periods of peak mosquito activity, especially after dusk, and perhaps to use various topical preparations on horses that can serve as mosquito repellents.

Q: Is there a threat to the equine industry in the United States?

In light of the experience gained from previous outbreaks of equine encephalitis in Europe that have been confirmed due to West Nile virus, it is unlikely that the horse industry in the United States is going to be confronted with major occurrences of this disease in the horse population in the years that follow the 1999 outbreak of encephalitis in New York State. There is the potential for this virus to become established in the northeast and other areas of North America and possibly other countries of the Americas. Only time will tell whether the occurrence in 1999 represents a single occurrence or the establishment of this virus and the potential for future occurrences of this disease in certain species of birds, humans, and horses in the years to come.

About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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