Hepatocystis in Baboons (Papio sp.)
American Association of Zoo Veterinarians Conference 2005

Robert E. Schmidt, DVM, PhD, DACVP

Zoo/Exotic Pathology Service, West Sacramento, CA, USA


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.


Clinical Pathology

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.

Gross Lesions

Multiple 1.0–5.0 mm yellow-white foci were present on the surface and throughout the hepatic parenchyma of affected baboons.

Histologic Lesions

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.

Literature Cited

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.


Speaker Information
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Robert E. Schmidt, DVM, PhD, DACVP
Zoo/Exotic Pathology Service
West Sacramento, CA, USA

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