Entopolypoides macaci, a Babesia-like parasite in Cercopithecus monkeys

Abstract

A description is given of a Babesia-like parasite found in the erythrocytes of two Cercopithecus pygerythrus monkeys probably from East Africa. Morphologically it seems identical with a parasite found by Mayer (1934) in Macaca irus monkeys from Java and named by him Entopolypoides macaci. On the other hand, the present African type differs from the Javan one in that it does not readily infect M. irus or M. mulatta monkeys; and it might well be named provisionally E. macaci (cercopitheci). Morphologically, the early forms are fine rings with a large vacuole but the more mature parasites form several fine long processes which are best seen under phase-contrast illumination. The cycle in the erythrocytes probably ends by division into four new parasites and it takes 3 days to quadruple the number. There is no synchronicity, such as occurs with malaria. The parasite was passed by syringe into Erythrocebus patas, Papio papio and Cercocebus galeritus monkeys in which it produced a light parasitaemia if they were intact, or an intense one (up to 70% erythrocytes parasited) if they were splenectomized. In both cases the bouts of parasitaemia are prolonged for weeks, and they may continue with relapses apparently for years. A light transient infection was produced in one splenectomized Macaca mulatta and in one out of two intact M. irus monkeys, but not in one M. arctoides (splenectomized), one Cebus albifrons, one C. apella, two Aotus trivirgatus and two Pan troglodytes (one splenectomized). Apparently the parasite readily infected African lower primates, hardly infected Asiatic ones, and did not infect American ones. Even in susceptible splenectomized monkeys, in which it produced prolonged intense parasitaemia, the parasite causes little pathogenic effect beyond a moderate anaemia. Attempts were made to transmit it through Rhipicephalus sanguineus, Dermacentor andersoni, Ornithodoros (sp.), Ornithonyssus bacoti and Aedes aegypti but they were unsuccessful. Probably the vector is an Ixodid tick. Chemotherapeutically the parasite was sensitive to a babesicidal compound, Imidocarb (3,3′-bis-(2 imidazolin-2yl) carbanilide) and to primaquine but not to chloroquine, pyrimethamine, pentamidine, Berenil or homidium.