In vivo assay of viability of amastigotes of Leishmania donovani.

Following intravenous (i.v.) injection of formalin-killed or ultraviolet-killed or ultraviolet-irradiated amastigotes of Leishmania donovani, the parasites could be identified in mouse liver at 5 min, but most amastigotes were digested by 3 hr or between 24 and 72 hr, respectively. An in vivo assay of viability, based on these observations, suggests differences in the viability of hamster amastigote populations. The identification of dead and/or dying amastigotes in the liver 24 hr after i.v. injection suggests that enumeration of amastigotes from Giemsa-stained slide preparations may include varying numbers of nonviable organisms.