August 2009

Eastern Equine Encephalitis in Maine and neurologic form of Equine Herpesvirus 1 in Pennsylvania

This week a horse in Troy, Maine died of EEE (Eastern Equine Encephalitis). The last Maine case of fatal equine EEE was last September, in Lebanon. In 2005, two other horses died of EEE in Berwick and Kittery. The concern with this case is that the disease, which is spread by mosquitoes and does not spread from horses to humans, has not been seen in an equine fatality in this area prior to now. Please communicate to your equine clients/producers/friends the following:

1. This disease is preventable with routine vaccination. Many are available, and often can be purchased at feed or pet stores for owner administration to their own horses. It's generally in combination with Tetanus, another important equine vaccination. This makes it a very available, affordable option.

2. The disease is harbored in birds. Mosquitoes bite infected birds, and become carriers. The mosquitoes then bite humans or other animals, infecting them. Horses are sensitive to the virus, but don't "concentrate" it as do birds or mosquitoes, so are not considered a risk for transmitting infections into mosquitoes or for directly infecting humans.

3. Please see http://www.cdc.gov/ncidod/dvbid/Arbor/eeefact.htm for more information on the CDC website. The CDC estimates there are about 5 human cases of EEE per year in the US. This site discusses symptoms and onset of the disease in humans.

A different equine disease, which is very transmissible to other horses but not a threat to people, has cropped up in Pennsylvania. An outbreak of the neurologic form of equine herpesvirus 1 has occurred at a boarding facility in Allegheny County during late July 2009. The risk of this highly contagious respiratory disease can also be reduced by vaccination, although as in most herpesviruses, latency of the infection can occur. Biosecurity is very important to reduce spread of this disease, as the virus is shed for 3 weeks or more by horses sick with the disease, and the virus can remain infective from the environment or the animal's hair coat for 2-7 weeks. In general, the signs of this syndrome are:

1. Inability to urinate and defecate

2. Ascending paralysis: unsteady on hind legs, then "dog sitting", then completely down

Horse owners should be aware of these 2 diseases, and discuss them with their veterinarians, especially if they are shipping horses to shows or fairs.