Dogs as sources and sentinels of parasites in humans and wildlife, northern Canada

A minimum of 11 genera of parasites, including 7 known or suspected to cause zoonoses, were detected in dogs in 2 northern Canadian communities. Dogs in remote settlements receive minimal veterinary care and may serve as sources and sentinels for parasites in persons and wildlife, and as parasite bridges between wildlife and humans. In the Northwest Territories, harvesting country foods is a key cultural activity and is important for sustenance; 75% of persons eat harvested meat and fish. Dogs fed fish and game can serve as indicators of parasites in these human food sources. Diet-associated zoonotic parasites detected in dogs included Diphyllobothrium spp., cestodes acquired by eating undercooked or inadequately frozen fish (found in humans throughout northern Canada); Alaria spp., trematodes acquired by eating frogs or paratenic hosts; and Toxoplasma gondii, tissue protozoans acquired by eating oocysts from felid feces or tissue cysts in intermediate hosts (a worldwide human pathogen). In aboriginal persons in northern Canada, seroconversion for T. gondii during pregnancy has been associated with diets that include caribou. High seroprevalence in dogs indicates that T. gondii is common in the study area; however, the source of exposure was not identified. Given potential consequences for infection of parasite-negative pregnant women, further research is warranted on the association of human toxoplasmosis with a diet of country foods in northern regions.
Toxocara spp. are nematodes that cause visceral and ocular migrans in humans, particularly children. Although Toxocara spp. are considered limited to more southern regions, their presence in puppies and adults in Fort Resolution suggests that completion of their life cycle at northern latitudes is possible. Continuing warming trends may lead to increased occurrence of this parasite in the north. Giardia sp. Assemblage A is a protozoan that causes gastrointestinal disease in humans. Isolation of this zoonotic strain was unexpected because dogs are typically infected with Assemblage D, and Assemblage A suggests transmission from humans to dogs. This finding highlights a need to further investigate the apparent emergence of Assemblage A in domestic and wild animals in remote northern regions and transmission patterns among dogs, wildlife, and humans (S.J. Kutz, unpub. data). Echinococcus spp. are cestodes that cause hydatid (E. granulosus) or alveolar cysts (E. multilocularis) in the lungs and livers of humans. Although a reduction in dog teams in northern Canada has resulted in decreased prevalence of E. granulosus spp., the distribution, epidemiology, and role of the more pathogenic E. multilocularis spp. are not well understood in this region. Uncinaria spp. and Toxascaris spp. are also occasionally reported as zoonoses; however, evidence for these findings remains equivocal.
Dogs can also be sources of disease in parasite-naïve wildlife populations. They were the source for devastating distemper outbreaks in lions in the Serengeti, and lice of presumed dog origin are causing serious disease in Alaskan wolf populations (K.B. Beckmen, pers. comm.). Neospora caninum detected in this study may be a new parasite in this ecosystem with potentially serious consequences for wildlife. The remaining parasites are presumed present in local wildlife and can have a negative effect on the health of dogs and wildlife. More detailed, quantitative investigation is required to evaluate the role of dogs as potential sources of new, or amplifiers of existing, pathogens for wildlife.
Our results highlight important health issues associated with the interface between dogs, wildlife, and humans in remote northern communities. Disease associated with parasites in this study is often subclinical but can have serious effects on health and productivity of humans, dogs, and wildlife (e.g., Giardia spp.). Although these parasites are relatively easy to control, there was no evidence that sporadic veterinary presence in Fort Chipewyan reduced parasitism. This finding emphasizes the need for a new approach to domestic animal healthcare in the north. Inaccessibility of communities, uncertain and changing roles of dogs, and current regulations in the veterinary profession restricting remote delivery of services hinder development of effective disease detection and preventative medicine programs. Innovative new methods for delivery of animal healthcare services are required. These methods should include long-term commitment to an integrated health approach, focusing on education, engagement, and development and support of local capacity for delivery of basic animal health services. Ongoing communication and partnerships between animal and human health professionals will enhance the effectiveness of such initiatives.

Emerging Infectious Diseases
January 8, 2008

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