Entopolypoides macaci (Babesiidae) in Macaca mulatta

Abstract

Natural infections with Entopolypoides spp. organisms were detected in 11 of 15 Macaca mulatta studied; 6 of these had undergone splenectomy and/or antirhesus lymphocyte globulin therapy. Serial transmission by intravenous injection of infected blood was accomplished, and the prepatent period decreased with successive transfers. Furthermore, Entopolypoides infection did not protect against superinfection with Babesia microti or Plasmodium cynomolgi, and treatment with primaquine phosphate and/ or quinine sulfate did not eradicate the Entopolypoides organisms. This study demonstrates that infection with Entopolypoides may be more common than suspected from previous reports and that the potential for infection of humans should be recognized. Entopolypoides macaci Mayer, 1934, was originally described in Macaca irus monkeys. These intraerythrocytic parasites are ringshaped in the early stages, but later become ameboid with polypoid arms of cytoplasm and dispersed chromatin particles. They are smaller than Babesia and Plasmodium organisms and morphologically distinct. No pigment is formed. In 1948, Fairbaim reported the presence of Entopolypoides organisms in Cercopithecus monkeys. Both of these investigators found that even heavy infection had little apparent effect on the host except for some fever reported by Mayer. In 1972, Hawking observed Entopolypoides in Cercopithecus monkeys and was able to infect a variety of nonhuman primates. Heavy infections (> 5% of erythrocytes containing parasites) were usually detected in splenectomized animals. A splenectomized Macaca mulatta developed a light parasitemia 28 days after inoculation of infected blood. Chronic, latent infection persisted for as long as 4 years in one Cercopithecus monkey. Pathological findings were mild and nonspecific. Hawking was unable to transmit infection using mosquitoes (Aedes aegypti or Anopheles maculipennis), mites (Ornithonyssys bacoti), or soft ticks (Ornithodorus spp.). Transmission by hard ticks (Rhipicephalus sanguineus and/ or Dermacentor andersoni) was under longterm investigation, but no positive results were reported. Similar observations were made by Mayer using Anopheles maculipennis and Rhipicephalus spp. Hawking also reported that the antimalarial drugs, chloroquine phosReceived for publication 7 March 1974. phate and pyrimethamine, were inactive against Entopolypoides and the babesicidal compounds, pentamidine isothionate and berenil, were also inactive against Entopolypoides; but imidocarb diproprionate, an experimental babesicidal drug, was highly effective in eradicating the infection in the one monkey treated. This paper reports on the accidental transmission of Entopolypoides macaci in Macaca mulatta and detection of these organisms in the blood of 10 of 14 other rhesus monkeys examined. Furthermore, the effects of antimalarial therapy and possible protection against infection with Babesia microti and Plasmodium cynomologi were also assessed. MATERIALS AND METHODS