Endemicity of toxoplasmosis in Costa Rica.

Toxoplasma infection can be transmitted to humans by ingestion of tissue cysts in meat or by ingestion of oocysts in cat feces or fecally contaminated soil. since meat is traditionally well cooked in Costa Rica and the authors were able to exclude meat and eggs from playing a role in transmission, they postulated that ingestions of oocysts should entirely explain transmission. To test this hypothesis, they studied seven populations in Costa Rica and serologically tested 883 people between 15 and 26 years of age. By interviews and surveys, they determined mode of living, soil contact, cat contact, and cat density. The infection rate in cats was studied by stool and serologic examination, and soil availability for defecation was determined from aerial photographs. Antibody was taken as indicating infection and was found to be acquired most actively in children and young cats. In a retrospective analysis, antibody prevalence in humans correlated highly with individual cat contact (both owned and stray), with cat density, with living in houses with wood floors and a crawl space underneath, and with living with cats on a cement floor. antibody prevalence in humans correlated negatively with soil availability to cats for defecation and with soil contact by humans, suggesting that oocysts may be transmitted optimally near house in areas where most terrain is covered by asphalt and concrete and little soil is available for defecation or for human soil contact. Cats acquire infection by eating intermediate hosts; 16% sparrows, 3.5% of mice and 12.5% of rats have been found infected. Favoring transmission are young non-immune cat populations, shade and moisture, older intermediate hosts, a high percentage of which have become infected, and concentration of houses in city blocks. Transmission is diminished when houses are dispersed or arranged along a road in an open rural setting, permitting dispersal of cat fecal deposits.