Leishmania in the chick embryo. II. Effects of inoculum size, strain origin and stage injected and infectivity of embryo-derived parasites for hamsters

SYNOPSIS. Amastigotes of Leishmani donovani strains 2S, 3S, 3K, Hm, Gm, and Et were inoculated intravenously into 14‐day chick embryos. The course of infection was followed by examinations of liver impression smears. With strain 33 at 33 C incubation, there was a 29‐fold increase at 6 days postinfection when the inoculum contained ∼4 × 106 amastigotes, but only a ∼6.3‐fold increase when ∼64 × 106 parasites were injected. Infection courses of several geographic strains were compared at 30, 33, and 35 C incubation. Although the results were variable, Sudan strains 2S and 3S appeared to be separate isolations of a single strain. The Burma (Et), Kenya (3K), and Mediterranean (Hm, Gm) strains appeared to be distinct, but confirming evidence of their distinctness should be sought using serologic, epidemiologic, clinical, and biochemical criteria. Strains 2S and 3S multiplied best at 33 C or below, but the embryos usually failed to survive at 28 or 30 C. Multiplication was inhibited partially at 35 C and completely at 37 C. Inoculation of strain 3S promastigotes into chick embryos resulted in a loss of parasites in 1 hr to 2 days postinfection. Only amastigotes were seen in embryos incubated at 28 and 33 C for 4 days. Hamsters infected with parasites passaged once in chick embryos died at median postinoculation times that were closely comparable to those noted among hosts infected with amastigotes from hamster spleen.