The Ontario Ministry of Agriculture and Food (OMAF) has announced that two Ontario, Canada, horses tested positive for Potomac horse fever (PHF) in early August.

"Samples collected from an anorexic and febrile horse in Essex County confirmed that the horse was suffering from PHF; the horse subsequently died," the department said in a veterinary update. "A horse in the Ottawa area also tested positive for PHF. It was exhibiting profuse watery diarrhea but is reported to be recovering."

Neither horse was vaccinated against the disease, the OMAF alert said.

PHF is caused by Neorickettsia risticii, an organism found in some flukes (a wormlike parasite) that infect aquatic snails and insects (such as caddisflies, mayflies, damselflies, and dragonflies)