Current status of food-borne parasitic zoonoses in Singapore.

Parasitic infections adopt a rather low profile in the highly urbanized setting in Singapore. Very few food-borne parasitic infections are encountered. Apart from a few reports of infections with Clonorchis/Opisthorchis, Taenia spp. and hydatid disease, there are no other citations of such helminthic infections. Seroprevalence surveys have shown the presence of toxoplasmosis in local meat animals (sheep, pigs and cattle) and Toxoplasma strains have been isolated from the pig, tree shrew (Tupaia glis), slow loris (Nycticebus coucang) and guinea pigs. Human toxoplasmosis is prevalent in Singapore. Anti-Toxoplasma antibodies are found in the normal population as well as in clinical cases (cervical lymphadenopathy, ocular disease and congenital toxoplasmosis). Carcasses/organs from meat animals (sheep, pigs, cattle) slaughtered at local abattoirs were examined for parasites. The main parasites found were Ascaris suum, Dictyocaulus, Metastrongylus, Cysticercus ovis, Fasciola hepatica and Sarcocystis spp. Pigs were also examined for trichinosis and, thus far, these have all been negative.

Toxoplasmosis in Singapore.

The present paper reports research done in the following areas in the Parasitology Unit of the Department of Microbiology, National University of Singapore: determination of anti-Toxoplasma gondii antibodies in different IgG subclasses; immunoblot analysis of the antibody response to T. gondii and identification of key reactive epitopes; production and characterization of monoclonal antibodies to T. gondii; and the development of an IgM capture ELISA. IgG1 is the dominant subclass involved in the humoral response to T. gondii. IgG3 and IgG4 may be produced at low but significant levels. IgG2 production was not apparent. Immunoblot analysis of the positive sera revealed that the major antigens recognized by IgG and IgM antibodies were of MW 22, 35 and 67 kDa. Many of the bands observed in blots with positive sera were also present in blots with negative sera. The 22 kDa band was seen in majority of positive sera and was generally absent in negative sera. Anti-Toxoplasma sera also revealed IgA antibodies. Immunoblot analysis of the antigen revealed a 14 kDa band that reacted with all IgA positive sera. From a panel of monoclonals produced against T. gondii, one monoclonal, 5F3 (A) was selected for development of a monoclonal based IgM capture ELISA for detection of antibodies to 22 kDa and 41 kDa epitopes of T. gondii.

Distribution and ecological consideration of Breinlia booliati infecting wild rodents in Malaysia.

Seven of the 18 species of lowland forest terrestrial and semi-arboreal murids were found naturally infected with Breinlia booliati. Of these, two species, Rattus sabanus and R. cremoriventer, were found to be the most preferred hosts. None of the murids from the highland, field or human-inhabited areas was infected. This could have been due more to the greater scarcity of the vectors in these habitats than to the susceptibility of the hosts. The absence of this parasite in the squirrels examined may be attributed either to host specificity or to the normal activity cycles or vertical stratification of the vectors, separating them in space and/or time from the squirrels. The pattern of dispersion of the parasite is influenced by the wide distribution of suitable hosts, and the hypothesis that the parasite is of forest origin is discussed.