Hepatocystis infection in baboons and Old World monkeys can lead to hematologic, gross and histologic changes. Even though the disease is subclinical the changes may lead to diagnostic confusion. The common hematologic, gross and histologic lesions and their significance are illustrated and discussed.
Hepatocystis kochi and H. simiae are malarial-type protozoa that are endemic in Old World nonhuman primates including baboons.3 Transmission is by insect vectors and the parasites are considered to be nonpathogenic.
Blood samples were collected from baboons introduced into quarantine. Tissue samples with lesions were obtained at necropsy from animals that died of a variety of causes.
Early gametocytes appeared as a vacuole in erythrocytes. In 4–5 days these developed into mature gametocytes, which were slightly larger than a normal erythrocyte and contained green-black pigment.
Multiple 1.0–5.0 mm yellow-white foci were present on the surface and throughout the hepatic parenchyma of affected baboons.
These varied from early changes (intracellular granules in hepatic parenchymal cells) to multilocular merocysts. An inflammatory response and eventually fibroplasia and scar formation were also seen.
Parasites can be found in the peripheral blood1 and do cause gross and histologic lesions,2 which could lead to confusion during physical/laboratory examination or during necropsy. This paper discusses and illustrates the hematologic, gross and histologic lesions seen in baboons with Hepatocystis infection.
1. Garnham, P.C.C. 1966. Malarial Parasites and Other Haemosporidia. Blackwell Scientific Pubs. Oxford. Pp. 856–860.
2. Strong, J.P., J.H. Miller, and H.C. McGill. 1964. Naturally occurring parasitic and other lesions in baboons. In: The Baboon in Medical Research. Proc. 1st Symp. on the baboon and its use as an experimental animal. Univ. Texas Press. Austin. Pp. 507–509.
3. Zeiss, C.J. and N. Shomer 2001. Hepatocystosis in a baboon (Papio anubis). Contemp. Top. Lab. Anim. Sci. 40:41–42.