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Contact with Echinococcus multi eggs shed by wolves, coyotes and foxes is the way that dogs and people become infected with the larval stages of this parasite. Photo: iStockphoto.com

Researchers hunt for tiny worm in B.C. wildlife

Most people living in developed countries like Canada don't think of tapeworms as a threat to human health, but a recent discovery in British Columbia may eventually change that perception.

In 2009, researchers at the Western College of Veterinary Medicine (WCVM) were part of a team that detected a European type strain of Echinococcus multilocularis (E. multi for short) in a liver sample taken from a dog that had lived near Quesnel, B.C.

It was B.C.'s first known case of E. multi — a zoonotic parasite that's responsible for alveolar hydatid disease (AHD), a deadly infection in people and dogs.

E. multi lives in the small intestine of wild carnivores such as wolves, coyotes and foxes and usually doesn't cause any harm to its host. But problems happen when its eggs are shed in the feces of the carnivore host. If those eggs are ingested by a rodent, they hatch and form many small cysts on the animal's liver. If a carnivore then ingests the infected rodent, the worm moves on to a new host.

In the wild, this cycle continues with virtually no negative effects on wildlife populations. But when people or domestic dogs accidentally ingest E. multi eggs, the resulting worms form destructive cysts in the host's liver and can spread to other parts of the body.

In Canada, only one person is thought to have developed AHD caused by E. multi acquired in the country. However, there have been Canadian cases where the person acquired AHD outside the country. It's also possible that cases have been confused with a related tapeworm (E. canadensis) or even with various forms of liver cancer.

Further work at WCVM by Karen Gesy, a Master of Science student, confirmed that E. multi was present in coyotes and foxes from the Quesnel area. The strain was identical to the one detected in the dog (the index case) and closely related to European strains of E. multi. This was a significant finding since the European strains may be more infective to humans than the strains commonly found in Canada.

Researchers were left with several key questions: how and when did European E. multi arrive in B.C. and how widespread is it in wildlife populations today? What is the risk to veterinary and public health?

Karen Gesy, now a research technician with Environment Canada, points out that red foxes could have brought E. multi to North America in the 1800s when they were shipped over from Europe for hunting purposes or use in fur farms.

Another possibility is that the parasite could have been imported with pet dogs since Canada has no legislation requiring that dogs must be tested or treated for parasites before entering the country.

"It's a potential way for zoonotic diseases to enter the country, especially where dogs can play the main host," explains Gesy.

It is possible that E. multi has been present in B.C. for some time and has simply gone undetected until now. However, Gesy says "we're seeing … a number of domestic dogs infected [with the larval stages of the parasite], which means it's a …[potential] public health problem or about to be."

Since contact with eggs shed by wolves, coyotes and foxes is the way that dogs and people become infected with the larval stages of E. multi, researchers want to know the locations and species in which the parasite is most likely to be found.

To help answer these questions, I spent the summer of 2014 hunting for E. multi in the gastrointestinal tracts (GITs) of wolves and coyotes that hunters and trappers had sent to the regional wildlife health offices in B.C. My project was part of parasite research work being conducted by WCVM researcher Dr. Emily Jenkins and her team members who work closely with B.C. wildlife veterinarian Dr. Helen Schwantje.

Once the animals' GITs arrived at the WCVM, I froze them at -80 degrees Celsius for a week so that any intact worms or eggs were non-infective. I then thawed the GITs and searched for worms in the small intestines so I could count the number of heads (scoleces) and save any fully intact worms. These worms were then genetically tested to determine the origin and diversity of worms present in B.C.

After completing the processing and genetic testing, I identified new areas of B.C. that had E. multi in wildlife. This information will be useful to hunters and trappers as well as wildlife and public health officials.

The good news is that the risk of E. multi infection to people and companion dogs can be minimized through careful management and education, says Gesy.

"A lot of other countries … that are [concerned about] E. multi infection have really strict regulations … [for importing] companion animals – they all have to be treated for parasites."

She suggests that people can reduce the risk to themselves and their dogs through regular veterinary care (including deworming), by minimizing their pets' contact with wildlife feces and rodents, and by practising proper hygiene. Veterinarians also need to be on the alert for dogs with the larval stages of this parasite, which can cause tumour-like lesions in the liver.

 

Anna Huber of Kelowna, B.C., is a second-year veterinary student who was part of the WCVM's Undergraduate Summer Research and Leadership program in 2014. Anna's story is part of a series of articles written by WCVM summer research students.
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