Emerging issues with Echinococcus spp. cestodes in Canada

Adapted from: E. Jenkins, Echinococcus spp. Tapeworms in dogs and cats. 20017. Clinician's Brief 15(7):14-18. www.cliniciansbrief.com/article/echinococcus-spp- tapeworms-dogs-cats

Zoonotic Echinococcus spp. tapeworms are emerging as a cause of canine and human disease in Canada.  Echinococcus canadensis is present across almost all of Canada, except the High Arctic and in the Atlantic provinces, where wolves, a key definitive host for the parasite, have historically been eradicated. However, E. canadensis has recently been detected in coyotes in southern QC and Maine, suggesting that the Eastern coyote may now be enabling the local life cycle of E. canadensis.  Hunting dogs and free roaming dogs in remote and rural areas are considered high risk for this parasite, which they contract by consuming hydatid cysts in the lungs or liver of cervids. People can become infected with this parasite by inadvertently consuming food or water contaminated with eggs of this parasite shed in dog, wolf, or coyote feces.  Human cases of cystic echinococcosis, or CE, are reported regularly across most of Canada, and there are hot spots of transmission in the northern territories and some regions of SK and MB. 

A close relative, Echinococcus multilocularis, once thought to be restricted to Arctic and prairie regions of Canada, now appears to be established throughout most of western Canada, including boreal regions of BC and the NT, and southern Ontario. Increasingly, cases of alveolar echinococcosis (AE) caused by E. multilocularis are being detected in dogs in BC, AB, SK, MB, and ON. As well, human cases of AE that may be locally acquired are being detected in AB and SK; previously, only one locally acquired human case of AE had been reported in Canada, although foreign acquired cases are detected occasionally. At moment, it seems that recently introduced European-type strains of E. multilocularis (rather than native strains long established in prairie Canada) are involved in both canine and human AE cases in Canada. These strains may have been introduced through importation of dogs, which highlights the need to test and treat dogs being imported into Canada for a wide range of infectious diseases and parasites, in addition to current regulatory requirements for rabies vaccination. 

It is unusual for dogs to develop AE (although this condition has been recognized in dogs in Europe since the 1990s).  Dogs traditionally play the role of definitive host, where adult cestodes inhabit the intestine and cause few, if any, problems for the dog (but do pose a risk for human health).  AE requires aggressive surgical and medical management in dogs and should be a differential diagnoses for liver masses, especially in younger dogs, in endemic regions. Confirmed intestinal infections of E. multilocularis and E. canadensis in dogs should be aggressively treated with an adult cestocide such as praziquantel. In endemic regions, dogs at high risk of consuming the larval stages of these parasites in wild rodents and cervids should be dewormed every 4-6 weeks. As no particular season of transmission is known, high risk dogs should be treated monthly with praziquantel year round.  We acknowledge that this is a costly drug and this will pose problems for shelters and low income owners. Until better diagnostic tests are available, prophylactic treatment and modifying behavioural and dietary risk factors are the best line of defense.

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