The protective effect of the epimastigote forms of the PF strain of Trypanosoma cruzi against a virulent homologous infection.

Epimastigotes are assumed to be non-infective forms of trypanosomes. However, epimastigotes of the PF strain of the Trypanosoma cruzi when injected in mice, in a single low dose, conferred on the animals a very good protection against challenge of a virulent homologous strain.