Comparative susceptibility of African green monkeys (Cercopithecus aethiops) to experimental infection with Leishmania leishmania donovani and Leishmania leishmania infantum.

The leishmaniases are global health problems that affect both humans and animals. The availability of nonhuman primate models is desirable for such important areas as testing candidate vaccines and newly developed chemo- and immunotherapeutic agents. Visceral leishmaniasis was experimentally induced in African green monkeys (Cercopithecus aethiops) by intravenously inoculating 10(7) amastigotes/kg of body weight of either Leishmania leishmania donovani of human origin (group 1) or L. l. infantum of canine origin (group 2). The infected monkeys were monitored for 12 weeks. The monkeys developed persistent infections, became emaciated, and lost between 9 and 22% of their body weights. Splenomegaly developed by 6 to 10 weeks postinfection. All infected monkeys developed normocytic, normochromic anemia (3.5 to 3.8 x 10(6)/microliters), leukopenia (3,000 to 3,700/microliters), and neutropenia of varying severity. Hyperproteinemia with hyperglobulinemia (5.22 to 6.12 g/dl) was present in all monkeys to various degrees. Antibody responses gradually increased to peak values at 2 weeks postinfection in the L. l. donovani group and by 6 weeks postinfection in the L. l. infantum group. Lymphocyte blastogenesis proliferation responses were mildly decreased in all infected monkeys at 10 to 12 weeks postinfection. Parasite numbers were consistently higher in the livers than in spleens, and parasites were present in smears or cultures of the liver, spleen, bone marrow, and lymph nodes. Contrasting data between the two groups included 20-fold-higher parasite numbers in the livers (3.23 to 9.48 x 10(9)) and 39-fold-higher parasite numbers in the spleens (6.7 x 10(8) to 2.69 x 10(9)) of group 1. Granulomatous inflammatory reactions of various severity and intensity were observed in the liver, spleen, lymph nodes, thymus, and bone marrow of all infected monkeys. Within the granulomatous inflammatory reactions, clusters of macrophages, often containing amastigotes, were present. The morphologic changes in the bone marrow suggested a myelophthisic disease and those in lymph nodes and spleen suggested a B-cell proliferation. The clinicopathologic changes, mild suppression of cell-mediated immunity, and high antibody response in all infected monkeys indicated that African green monkeys can be a useful laboratory model for studying the clinicopathologic and immunopathologic changes induced by both L. l. donovani and L. l. infantum.