Prevalence of Antibody to Toxoplasma among Alaskan Natives: Relation to Exposure to the Felidae

In an assessment of the role of felids in transmitting toxoplasmosis to humans, sera from 1,572 Alaskan natives with different degrees of potential exposure to Felis catis and Lynx canadiensis were examined for antibody to Toxoplasma by the indirect fluorescent antibody test and the indirect hemagglutination test. Prevalence varied widely irrespective of geo-ethnic classification. Overall, approximately 28% of the sera examined had antibody (detectable by the indirect fluorescent antibody test) at a dilution of 1:16. A complementary assessment, in which the indirect hemagglutination test was used to titrate sera for end points of antibody to Toxoplasma, yielded a prevalence rate of about 16% at a dilution A 1:32. Previously, toxoplasmosis was thought to be absent in Eskimos. Contrary to expectation, felids could not be excluded as possible vectors of infection even in the remotest regions of the far north. Animals used as food by Alaskan natives may also have contributed to the relatively high prevalence rate found, but virtually nothing is known about the epizoology of toxoplasmosis in the Arctic. How much of the prevalence of antibody to Toxoplasma among humans results from exposure to members of the cat family, Felidae, and how much from ingestion of raw or partially cooked meat or other animal products containing viable encysted Toxoplasma is a moot question. Transplacentally and occupationally acquired infections obviously contribute only slightly to the variable, but high, prevalence found in many human populations [1]. Epidemiologic evidence accumulated thus far does not permit evaluation of the relative importance of felids vs. animal flesh in transmission in free-living human societies. Wallace collected serologic evidence from ecologically simple islets in the western Pacific within 10' of the equator that suggests that cats may play a major role in the transmission of toxoplasmosis to humans in that setting [2, 3]. In a study in Seattle, Washington, prevalence among individuals who said that they had had a pet cat sometime during their lives was significantly greater than among those who denied having had