Course of infection of Leishmania donovani in hamsters inoculated by the intraperitoneal route.

Groups of golden hamsters were inoculated intraperitoneally with a logarithmic dilution series of L. donovani obtained from homogenized hamster spleen tissue. The prepatent period and median time to death were determined at each dosage level by examining subgroups of animals at various intervals postinoculation. Patent infections were detected by examination of spleen and liver impression smears stained with Giemsa's stain and by inoculation of culture tubes containing Tanabe's medium with ground spleen tissue. The median time to death at each dosage level was compared to that resulting from intracardially induced infections. Both the prepatent period and median time to death were increased at each 10-fold reduction in inoculum size following intraperitoneal injections. The median time to death was greater in intraperitoneally induced infections than intracardially induced infections for each dosage. The culture method was a more sensitive means of demonstrating parasites. The hamster has long been used as a diagnostic tool in the study of leishmaniasis. Tissue from suspected human or animal infections is injected into the animals and evaluated by examining spleen and liver impression smears for leishmaniform parasites and by examining culture tubes, inoculated with hamster tissue, for leptomonads. The route of hamster inoculation is a critical determinant of the course of the infection. Intracardial injections induce consistently reproducible infections (Stauber, 1955, 1958) whereas intraperitoneal inoculations cause more variable results. In addition, both the prepatent period and the time to death are longer when the intraperitoneal route is used. The ease of the intraperitoneal injection technique, however, in spite of the subsequent problems, has made it the more preferred method. Consequently, an attempt was made in this work to evaluate the leishmanial infection in terms of prepatent periods and median times to death following intraperitoneal inoculations of different dosages of parasites. MATERIALS AND METHODS Groups of golden hamsters were inoculated intraperitoneally (IP) with 10-fold dilutions of Leishmania donovani (Khartoum strain) obtained from homogenized hamster spleen. Subgroups of one to 10 hamsters were subsequently killed at various intervals, and the patency of the infections Received for publication 19 September 1966. * Supported by USPHS Research and Training Grants AI-00092 and AI-00187 from NIAID. t Present address: Department of Zoology, University of Georgia, Athens, Georgia 30601. 641 was determined by the following methods: (1) by finding at least one parasite per 1,000 organ cell nuclei counted on spleen and liver impression smears stained with Giemsa's stain, (2) by positive cultures of leptomonads from known amounts of ground spleen tissue in Tanabe's medium following 2 to 3 weeks' incubation at 25 C (Hanson and Stauber, 1964). Total parasite counts from impression smears were determined by the method of Stauber (1955, 1958). The last examination period is referred to as the median time to death (MTD). This represents the time when half of the animals in the final group had died, and the remaining ones were examined for parasites.