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Stool specimens from 89 high-risk, sexually active homosexual men were screened for enteric protozoal cysts. Patients whose specimens contained nonpathogenic cysts were investigated further by examination of fresh purged specimens. A total of 27 of the initial specimens (30%) contained protozoal cysts. Twenty-three patients (26%) harbored pathogens. There were 18 cases (20%) of amebiasis and 11 cases (12%) of giardiasis. Six men (7%) had concurrent amebiasis and giardiasis. The presence of infections correlated with a history of anilingus but not with place of birth, travel, or history of symptoms. The exceptionally high rate of prevalence of intestinal protozoal infection in this population suggests that enteric protozoal infections are important among sexually transmitted diseases.

Increasing travel, migration and other forms of international exchange have given a new importance to imported diseases in Canada. This is reflected in the maintenance of an immigration medical screening program, the development of specialized clinics in major cities, increasing interest in tropical medicine and international health, and the designation of a national reference centre for parasitology.The introduction of a point system for immigration selection in 1967 gave rise to a burgeoning influx of people from developing countries that may have plateaued only within the past year. While tuberculosis is probably the single most important health problem in immigration, parasitic infections are of increasing concern. The popularity of overseas travel among Canadians is now also a major factor in the introduction of exotic diseases into Canada. Importation of disease by international trade is far less common than by travel and immigration.On a community health scale a system of monitoring trends of immigration to Canada and travel of Canadians to and from countries with a known risk would likely provide the best indicator of trends in disease importation. Thus, there was an increase of almost threefold (11.6% to 31.1%) between 1965 and 1975 in the proportion of immigration to Canada from countries with a malaria risk and a 2.78-fold increase between 1967 and 1974 in the overall amount of Canadian travel to such countries from which statistics were available.

In two cases there was simultaneous or sequential occurrence of amebiasis, shigellosis, and giardiasis in male homosexuals. Enteric pathogens may, under the proper conditions, be venereally transmitted. In particular, the sexual practices of male homosexuals, most significantly, oral-anal contact, appear to provide the necesseary link for transmission. Evidence suggests that this is a growing problem.

Naegleria fowleri, a free-living ameboflagellate, is the causative organism of primary amebic meningoencephalitis. Intranasal inoculation of N. fowleri in mice produces an infection similar to human disease. Mice immunized with live N. fowleri by intraperitoneal injection were found to be more resistant to subsequent intranasal challenge. These results may provide a lead to the development of immunotherapy for this virulent disease for which satisfactory chemotherapy is presently unavailable.