Tiny parasite could lead to big health problems

Echinococcus multilocularis (or E. multilocularis) is a parasite that can cause a disease called alveolar echinococcosis (AE). Since this disease is zoonotic (can be spread from animals to people), that’s how a veterinary student like me had the chance to work last summer with the Public Health Agency of Canada (PHAC) on educating Canadians about this parasite.  

Understanding the parasite’s life cycle is key, so let me walk through it with you.

E. multilocularis is a small worm with a life cycle that involves two different animals. The first animal is a member of the canid family such as a dog, coyote, fox or wolf. The adult worm lives in the intestines of the canid and lays eggs that are tiny, sticky and incredibly resilient as they pass out of the animal through the feces.

The second animal is normally a rodent that eats these eggs. Once inside the rodent, they hatch into larvae that migrate to the liver where they grow like a cancer, causing AE. The life cycle begins again if a canid eats the rodent that’s housing the larval worm in the form of AE.

So how can E. multilocularis and AE affect you? That ties into my work with PHAC. My job was to create educational web pages about the parasite and the disease. These online resources will be used to educate people about this emerging threat and its serious implications for public health.

Although E. multilocularis usually minds its own business cycling in wild animals, the problem arises when people enter the parasite’s life cycle by accidentally eating the eggs from canid feces. Remember that these eggs are very small and resilient, so they remain in the environment long after the feces have disappeared.

And just how do people unknowingly ingest these eggs? Their pets’ actions could put people at risk: dogs may roll outdoors and bring in the parasite’s eggs on their fur or they may suffer from an intestinal infection caused by eating small rodents. As well, people could eat fruit or vegetables from areas visited by infected canids.

When the larvae spread to a human’s liver and cause AE, the disease is like a cancer as it grows out of control — leading to severe liver damage. Although early detection is key to successful treatment, people may not show any symptoms of the disease for five to 15 years after infection. If left untreated, there’s a 90 per cent fatality rate for humans infected by E. multilocularis.

“It’s probably time that we got this parasite more on the radar so that it isn’t missed,” says Dr. Emily Jenkins, a professor in the Western College of Veterinary Medicine’s Department of Veterinary Microbiology.

She’s an expert on E. multilocularis and has been monitoring its spread across Canada since 2009 when the first case was seen in a dog from British Columbia.

“Dogs have really been our ‘canaries in the coal mine,’ telling us that the parasite has been showing up in new places,” says Jenkins.

And what is it about dogs that make them our sentinels for this disease? Like people, dogs can get the liver/larval form of the parasite; however, they don’t have that five- to 15-year asymptomatic period. Dogs show their infections much more quickly, in a matter of months to a few years.

Last summer we identified 26 dogs with AE. Part of my summer job was to study these cases and gather as much information about the disease as possible so we can alert veterinarians to the clinical signs of E. multilocularis.

Dogs are showing these infections now, and dogs are living in similar environments to their owners. If people take five to 15 years to show their symptoms, researchers expect to see a rise in human cases of AE in the next five to 15 years.

But since the disease progresses faster in immune-suppressed humans it could start to show up sooner — a scenario that appears to be playing out in Alberta where about half of the current human cases of AE are immune suppressed.

“The only way out of this is to take a One Health approach,” says Jenkins. “We need to engage human physicians in management of these cases so that they are giving the right information to at-risk people.

“We know that human outcomes are way better, just like canine outcomes are way better, the earlier we detect it.”

As part of my research, I spoke with Dr. Stan Houston, a physician from the University of Alberta and an expert in E. multilocularis. He has been compiling records of all human cases of AE, and as of July 2019, he has identified 14 cases in Alberta

“We should be pooling our experience in terms of these liver lesions in dogs,” says Houston, agreeing with the need for involving both human and veterinary health organizations in approaching this disease.

“Clearly the human cases and the dog cases are both telling us something about the epidemiology of the disease. We should be sharing that information.”

Both Houston and Jenkins hope that people will learn from their research and use their awareness to avoid infection.

Houston advises people to take preventive measures so they’re not accidentally ingesting the parasite’s eggs: “Wash your hands after handling your pet, and wash your produce from any garden where canids might be wandering.”

Jenkins emphasizes that this problem can’t be solved by shooting coyotes.

“Shooting periurban coyotes will just bring in new coyotes that may be higher risk for E. multi because they have been subsisting mainly on wild rodents … and they tend to be marginal animals that are less healthy to begin with and couldn’t hold prime territory,” says Jenkins, adding that the parasite is found in other wildlife hosts besides coyotes such as foxes, wolves and rodents.

“I don’t want people to demonize wildlife [and say,] ‘They are the source of all of these nasty parasites — let’s shoot them all!’”

For me, the past summer was an amazing opportunity to span the worlds of veterinary and human medicine and influence the lives of two-legged and four-legged Canadians alike. I worked from two different angles of a problem, finding solutions to an emerging threat — a parasite that I have grown to love, in my own nerdy way.