The Indian Langur: Preliminary Report of a New Nonhuman Primate Host for Visceral Leishmaniasis

Described are the susceptibility of the Indian langur (Presbytis entellus) to Leishmania donovani and the consequent haematological and serum biochemical changes. The host response to antileishmanial chemotherapy and the immunological profile were also examined. Each langur was inoculated intravenously with 1 x 10(8) amastigotes; a spleen biopsy carried out on day 35 post-infection (p.i.) revealed 10-13 L. donovani bodies per 500 cell nuclei, which reached a maximum of 130-195 at death (day 105-110 p.i.). The infected monkeys lost body weight, developed severe anaemia, lymphocytosis, hyperproteinaemia, hypergammaglobulinaemia, hypoalbuminaemia and an increase in the level of alkaline phosphatase and alanine aminotransferase (AAT). Treatment with sodium stibogluconate (60 mg Sb5+ per kg body weight intramuscularly for 10 days) reduced the number of spleen parasites (0-1 amastigotes per 500 cell nuclei) but after the therapy the parasites appeared in the skin, which had previously been free of infection. Relapse occurred on day 30 post-treatment (10-24 amastigotes per 500 cell nuclei) and the parasites were resistant to repeat intensive therapy (120 mg Sb5+ per kg per day x 30 days). The stibogluconate treatment caused a proportionate reduction in the haematological and biochemical parameters to normal values except for alkaline phosphatase and AAT, which remained elevated. The level of IgG antibodies, which rose during the infection, rapidly fell to the pretreatment value following the first therapeutic schedule and then increased a second time coinciding with relapse. Our findings suggest that langurs could serve as acceptable models for human visceral leishmaniasis.