C. Gattii Fungus May Not Pose Serious Equine Threat

A fungus making its way down the western US from Canada may not pose a serious threat to horses, according to researchers familiar with the situation. A report from Duke University Medical Center on Cryptococcus gattii and its movement from Canada into Washington, Oregon, and Idaho made headlines recently as a "potentially lethal fungus," but not only is it rare, horses do not often appear to be affected.

Edmond J. Byrnes III, a microbiologist at Duke University, is the lead author of a report on C. gattii movement that appeared in the online journal PLoS Pathogens. The fungus has killed people in the US, often because its emergence in the US is new and physicians haven't known to look for it. The spores are inhaled and take root in the lungs before spreading through the body.

"This fungus has been considered a tropical fungus, but emerged to cause an outbreak in the temperate climes of Vancouver Island in 1999 that is now causing disease in humans and animals in the United States," said the researchers in the report.

However, Byrnes noted that the fungus "is still very rare."

When the 1999 outbreak of C. gattii occurred on Vancouver Island in Canada, only one horse tested positive for the fungus post-mortem, whereas C. gattii was found more often in many wild species of animals as well as in cats and dogs.

Colleen Duncan, DVM, Dipl. ACVP, now an assistant professor in the Department of Microbiology, Immunology and Pathology at Colorado State University, did her masters thesis at the University of Saskatchewan on the veterinary aspects of C. gattii in British Columbia.

"We swabbed the noses of more than 100 horses and did a fungal culture," Duncan recalled recently. "We also conducted blood tests to see if it was circulating in the bloodstream. We found C. gattii in the noses of a handful of horses but no positives in the blood. None of the horses were sick or ever became sick.

"While there have been equine cases, it does not seem to be a significant pathogen of horses," she added.

Karen Bartlett, PhD, an associate professor at the School of Environmental Health at the University of British Columbia, noted that to date at least two horses have died of C. gattii in British Columbia.

"In both cases, the horses had pneumonia," Bartlett said. "It is important to let people know that although rare, horses CAN be ill with Cryptococcus gattii infection."

Symptoms mimic many other conditions in the horse--general lethargy, dullness, and off feed. Duncan advised owners to seek veterinary attention if their horses show these symptoms in order to diagnose any potential underlying problem.

The report on the movement of C. gattii, "Emergence and Pathogenicity of Highly Virulent Cryptococcus gattii Genotypes in the Northwest United States," can be found in PLoS Pathogens.

About the Author

Tracy Gantz

Tracy Gantz is a freelance writer based in Southern California. She is the Southern California correspondent for The Blood-Horse and a regular contributor to Paint Horse Journal, Paint Racing News, and Appaloosa Journal.

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