Encephalitis In California

Eastern equine encephalitis (EEE) virus or an unrecognized, but very similar, virus, was isolated from the brain of a horse which died on April 21, 2000, in Ventura County, California. Essentially an East Coast disease, EEE rarely has been diagnosed west of the Mississippi and Texas.

The horse appeared at shows in Utah and California prior to its death. No other in-contact horses have shown clinical signs of the disease or had been in any EEE-endemic areas in the preceding weeks. The affected horse and 27 other animals were vaccinated the week before for EEE. No other horses became ill. According to Michelle Jay, DVM, Public Health Veterinarian for the California Department of Health Services (DHS), the virus was initially isolated at the National Veterinary Reference Lab. For confirmation, more samples were sent to the DHS virus and rickettsial disease lab, and to the center for vector-borne disease research at the University of California, Davis. The National Veterinary Service Laboratory is testing the vaccine batch used on the herd for safety.

The virus is being examined genetically at UC Davis and the United States Army Medical Research Insitute in Infectious Diseases to confirm it as a possible variant of EEE. "We feel it would be prudent to admit to the possibility that this could be a similar, but different, virus, that was previously undescribed, until we're sure that it was EEE," said Robert M. Levin, MD, Ventura County Public Health Officer. Officials believe there is minimal risk to horses and humans, as there must be widespread infection of mosquitoes and birds for the spread of disease to occur. A sentinel chicken flock is kept across the road from the facility to monitor for the evidence of circulation of infectious disease.

"The mosquito population is extremely low, and when the mosquitoes collected were tested, they were negative," said Stan Husted, Senior Public Health Biologist for the California Department of Health. "We checked our sentinel chickens for antibodies (against encephalitis), and they were negative as well."

Officials will continue to investigate in order to discover how the horse contracted the disease.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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