Leishmania donovani: clinical, hematologic and hepatic changes in squirrel monkeys (Saimiri sciureus)

Clinical signs, parasite densities, and hematologic and hepatic changes were studied in 7 squirrel monkeys (Saimiri sciureus) each of which was inoculated intravenously with amastigotes (5.0 X 10(7) per kg body weight) of a Khartoum strain (WR 378) of Leishmania donovani. One control monkey was inoculated with uninfected hamster spleen homogenate. Five of the infected monkeys recovered spontaneously from visceral leishmaniasis by 8 to 15 wk postinoculation (wk PI) and 2 of the infected monkeys died at 39 and 59 days PI, respectively. All monkeys inoculated with L. donovani experienced a slight body weight loss, mild but significant anemia, lymphocytosis and an inconsistent neutropenia. Liver parasite densities could be quantitated from liver imprints from 2 to 8 wk PI and reached a maximum mean of 6.3 X 10(7) amastigotes/g liver at 4 wk PI in Experiment 1 and 13.4 X 10(7) amastigotes/g liver at 6 wk PI in Experiment 2. None of the liver imprints contained parasites at 15 wk PI. The characteristic histopathologic findings in liver biopsy and necropsy samples were multiple granulomas consisting of macrophages (some of which contained parasites), lymphocytes and plasma cells. The squirrel monkey is a moderately susceptible host for L. donovani. Squirrel monkey visceral leishmaniasis has a sustained course and certain clinical, hematologic and pathologic characteristics which are similar to human visceral leishmaniasis.