A comparative study of infections with rodent isolates of Giardia duodenalis in inbred strains of rats and mice and in hypothymic nude rats.

Giardia isolated from mice and rats have been identified as Giardia duodenalis by morphological criteria. No differences in the electrophoretic mobilities of 28 enzymes were detected between the mouse and rat isolates or between these isolates and human and cat isolates. Infections with both rodent isolates have been studied in several strains of inbred rats. No significant differences were detected between the rat strains, with the mouse isolate producing a self-limiting infection and the rat isolate a chronic infection. After the primary infection was eradicated with metronidazole, all strains of rats were resistant to reinfection with the homologous isolate. Both isolates produced chronic infections in hypothymic nude rats. BALB/c mice were found to be relatively resistant to primary infection with either isolate but C3H mice became infected chronically with the mouse isolate and experienced a prolonged infection with the rat isolate. These findings resemble those observed with infections with G. muris in the same strains of mice (Roberts-Thomson & Mitchell 1978). It is suggested that infections with G. duodenalis in rats may offer a model for giardiasis that is based on organisms related closely to G. lamblia. Comparative studies using the two rodent isolates may lead to a better understanding of how the parasite establishes as a chronic infection and which antigens induce protective immune responses.