Toxocara seroprevalence in Canada-Climate, environment and culture

Human infection with larvae of canine and feline roundworms belonging to the genus Toxocara can lead to devastating visceral, neural or ocular larvae migrans disease. However, such overt disease represents a fraction of cases. Far more common is covert toxocariasis, a less severe, but clinically symptomatic form of disease, and those who are exposed to infective larvae and seroconvert, but appear to be asymptomatic. Canada represents a unique epidemiological environment for Toxocara infection and exposure. Although the freezing conditions of the vast Arctic Tundra region of the North are thought unlikely to support the lifecycle of Toxocara spp., exposure and seroconversion does occur in people belonging to Inuit communities of this region. Further south, in the sub-Arctic of northern Quebec and Saskatchewan, there is a higher seroprevalence in many Canadian First Nations communities. The epidemiology of these infections is different to that seen in the non-Indigenous communities of the Humid Continental region. Poverty and climate play a major part in the risk of Toxocara seropositive status in Canada, but other factors such as unique cultural practices, population density of humans and reservoir hosts, and contact with wildlife are also factors in exposure and subsequent seroconversion in Canadian communities. This review discusses previous Toxocara seroprevalence studies performed in Canada, summarizes the data for domestic and wild animal reservoir hosts of Toxocara canis, Toxocara cati, Toxocara vitulorum and the closely related helminth, Toxascaris leonina. It also discusses how the unique and varied aspects of climate, culture and environment impacts human Toxocara exposure in Canada.