Studies of the Exoerythrocytic Stages of Simian Malaria VI. Plasmodium hylobati

Abstract

Exoerythrocytic schizonts of Plasmodium hylobati were found in hepatic tissue acquired 7 and 14 days following intravenous inoculation of a gibbon (Hylobates moloch) with sporozoites from Anopheles balabacensis balabacensis. In addition, tissue schizonts were observed in hepatic tissue acquired 7 days after intrahepatic inoculation of an owl monkey (Aotus trivirgatus) with sporozoites also from A. b. balabacensis. While the morphologic features of the exoerythrocytic stages were not sufficiently distinctive, the size difference may be adequate to differentiate this species from other tertian plasmodia of nonhuman primates. This paper is the sixth in a series on the exoerythrocytic (EE) stages of simian malaria (Held and Contacos, 1967; Held et al., 1967a, 1968; Sodeman et al., 1969a, 1969b). The last paper in this series dealt with the EE stage of Plasmodium jefferyi, one of four malaria species described from the gibbon (Warren et al., 1966). The present report describes the EE body of another species of gibbon malaria, P. hylobati, in the gibbon and in the owl monkey. This species of malaria has a tertian periodicity and was initially described by Rodhain (1941) in a Hylobates moloch gibbon from Java. MATERIALS AND METHODS An H. moloch gibbon, harboring a natural infection of P. hylobati, was made available for study by Professor P. C. C. Garnham. The details of the history of this gibbon were described by Collins et al. (1972). Upon arrival, thick blood smears demonstrated a very low-grade parasitemia. Splenectomy (Sodeman et al., 1970) was performed which resulted in a marked elevation of parasites in the peripheral blood. Within 6 days, gametocytes appeared in the peripheral circulation which proved infective to insectary-reared Anopheles balabacensis balabacensis mosquitoes. The method used in the infection and maintenance of the mosquitoes, as well as the details of the sporogonic cycle, are reported elsewhere (Collins et al., loc. cit.). Eight days after splenectomy, the parasite count reached 315,000/mm3, and the gibbon was given a curative dose of chloroquine. Sporozoites were harvested in 10% monkey serum saline from salivary gland preparations of A. b. balabacensis mosquitoes after 11, 12, and 13 days of extrinsic incubation. Sporozoites from 95 Received for publication 18 May 1971. * Present address: University of Michigan Medical Center, Department of Pathology, Ann Arbor, Michigan 48104. pairs of heavily infected glands were inoculated intravenously into the same gibbon that yielded the original infection, 10 days after completion of chloroquine therapy. At the same time, triturated bodies of the same mosquitoes from which sporozoites had been harvested were inoculated intravenously. Sporozoites from 20 pairs of heavily infected glands after 13 days of extrinsic incubation in A. b. balabacensis mosquitoes were inoculated at laparotomy directly into the liver of an owl monkey (Aotus trivirgatus) that was free of malaria, and the site of inoculation was tagged with a stainless steel wire after the technique of Held et al. (1967b). No antibiotic medication was given after the inoculation of sporozoites. Seven and 14 days following inoculation of the gibbon and 7 days following intrahepatic inoculation in the owl monkey, hepatic biopsies were performed. Tissues acquired at the biopsies were fixed in Caroy's fluid, embedded in paraffin, and sectioned at 1, 2, 3, and 6 /L. These sections were stained with Giemsa by the technique of Shortt and Cooper (1947) as modified by Eyles (1960). The photomicrographs were made with a Zeiss photomicroscope.