A tapeworm that can infect dogs and humans has shown up in Ontario, leaving horse owners wondering if their equine partners are also at risk.

The Echinococcus multilocularis tapeworm is spread by coyotes and foxes that eat infected rodents, like field mice. The coyotes and foxes don’t get sick themselves, but the parasite eggs in their feces can cause a potentially fatal illness in dogs that consume their feces, called alveolar echinococcosis (AE). In turn, dogs that eat infected rodents don’t appear ill, but can pass the infection to humans via parasite eggs in their stools.

The risk to horses, though, is quite low, according to Dr. Scott Weese of the Ontario Veterinary College (OVC). He said, “As far as we know, it’s not a major issue in horses. The parasite has been found in the livers of horses before, not in Canada, so presumably there is some risk if a horse eats canid feces that contain eggs. However, the risk of a horse in Canada developing the disease is probably very low.”

Fellow OVC researchers, including Professor Andrew Peregrine, Ph.D. student Jonathon Kotwa and a team from the Department of Pathobiology, conducted a recent study which found the E. multilocularis tapeworm in nearly one in four coyotes and foxes they tested in southern Ontario, suggesting the potentially dangerous parasite is now well established in the region.

Until recently, Ontario was thought to be free of E. multilocularis, which has historically been mostly confined to the Prairies.

Dr. Weese said the best way to protect your dogs and yourself is to minimize their exposure to such wildlife and to implement an appropriate deworming protocol. “For dogs, the main things are avoiding eating coyote/fox feces and small rodents. That can be a challenge, though,” he said.

“Monthly deworming with a drug that kills tapeworms – routine dewormers used in dogs don’t – can be done to reduce the risk of the dog developing an intestinal infection, something that’s rarely a health problem for the dog, but which lets the dog be a risk to others, including people.”

When the parasite eggs are ingested by a dog, they hatch and migrate to the liver and develop alveolar hydatid cysts. If left untreated, the damage can be fatal, and can also spread to other organs. In humans, the infection progresses over several years, causing tumour-like lesions, usually in the liver. Treatment can be complicated and expensive, typically requiring surgery and drug therapy. If left untreated, it will spread to other organs and eventually become fatal.

Read more about the OVC study here.