JPC SYSTEMIC PATHOLOGY
SIGNALMENT (JPC #2317402): African green monkey (Cercopithecus aethiops)
HISTORY: Incidental finding at necropsy
HISTOPATHOLOGIC DESCRIPTION: Liver: Multifocally and randomly affecting approximately 15% of the hepatic parenchyma are scattered, variably sized, up to 4mm, granulomas characterized by a central area of eosinophilic cellular and karyorrhectic debris (lytic necrosis) admixed with abundant degenerate eosinophils and neutrophils, basophilic material (mineral), surrounded by moderate numbers of epithelioid macrophages, eosinophils and few multinucleated giant cells, further surrounded by plasma cells, lymphocytes, few fibroblasts and minimal fibrous connective tissue. Adjacent hepatocytes are frequently pale with swollen cytoplasm (degenerate), or, less commonly, shrunken with hypereosinophilic cytoplasm and pyknosis (necrotic). Multifocally associated with granulomas or randomly scattered within the parenchyma there are round to oval protozoal merocysts ranging from 300-1800 um in diameter with a thin eosinophilic hyaline capsule and containing numerous oval to elongate to irregular 25X50um schizonts, which have a 2um eosinophilic capsule imparting a internally septate appearance to the merocyts, and are filled with abundant 2-3 um basophilic merozoites. Larger, more mature merocysts undergoing various stages of degeneration or rupture, have a large central cavitation with fibrillar eosinophilic material and a basophilic merozoites scattered througout. There are low numbers of portal/periportal lymphocytes and plasma cells as well as scattered macrophages and hepatocytes which contain brown granular pigment (hemosiderin).
MORPHOLOGIC DIAGNOSIS: Liver: Granulomas, eosinophilic, multiple, random, with protozoal merocysts, etiology consistent with Hepatocystis kochi, African green monkey (Cercopithecus aethiops), nonhuman primate.
ETIOLOGIC DIAGNOSIS: Hepatic hepatocystosis
CAUSE: Hepatocystis kochi
- Apicomplexan hemoprotozoan which is the most common malaria-type parasite of African primates; does not infect humans
- Distribution: India to the East Indies; Africa – south of the Sahara Desert
- Family Haemospororida; also includes the genera Plasmodium, Haemoproteus, and Leucocytozoon
- Hosts include Old World monkeys: African green monkeys, guenons, mangabeys, baboons, patas monkeys, colobus monkeys, Formosa rock macaques, other Macaca and left monkeys) and apes (gibbons)
- Species reported in nonhuman primates include H. kochi, joyeuxi, H. bouillezi, H. cerocopitheci, H. simiae, H. semnopitheci, and H. taiwanensis
- Typically incidental; primary effect is interference in research data
- Little or no inflammatory response to immature merocysts
- Suppurative response generated toward the maturing merocyst as merozoites are released
- Progressive increase in histiocytes, formation of granulomas, and eventual resolution as a fibrous scar
- kochi’s life cycle:
- Resembles Plasmodium, however asexual schizogony does not take place in erythrocytes of the host but in the liver, schizonts mature in 1-2 months, leading to characteristic cysts known as merocysts, which are visible grossly
- Indirect with midges (Culicoides, ) which is the biological vector for the gamont stage
- Merocysts rupture, releasing merozoites which invade erythrocytes; develop into gametocytes
- The midge ingests infected blood
- Microgamonts (microgametocytes) undergo repeated nuclear division to form microgametes; fertilization and sporogony occurs to produce sporozoites
TYPICAL CLINICAL FINDINGS:
- Typically the infection is asymptomatic
- Mild microcytic anemia
TYPICAL GROSS FINDINGS:
- Random, multifocal 2-4 mm, grayish-white, somewhat translucent foci on the surface of the liver and/or white fibrotic scars
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Multifocal merocysts in variable stages of maturation may reach 4 mm in diameter
- Mature merocysts form large lakes of colloid in their center and containing numerous schizonts filled with merozoiteswhich may be further surrounded by neutrophils
- Granulomatous and eosinophilic inflammation (granuloma formation) following cyst rupture with surrounding fibrosis
- Trophozoites and microgamonts and macrogamonts within erythrocytes
ADDITIONAL DIAGNOSTIC TESTS:
- Identification of parasite in thick or thin blood smears
- Hepatic lesions with organisms are diagnostic
- Giemsa – microgamonts in the erythrocytes have an unusual nucleus with a large oval pink nucleoplasm
- Plasmodium – do not form mature merocysts with a central area of colloid
- Tuberculosis - granulomas without merocysts
- Species infected by different Hepatocystis: Multiple nonhuman primates of Africa; fruit bats; oriental squirrels; deer mice; hippopotami
- Benirschke K, Farner F, Jones T. Protozoal and metazoal diseases. In: Pathology of Laboratory Animals. New York, NY: Springer-Verlag; 1978:1612.
- Flynn R. Sporozoans and neosporans. In: Parasites of Laboratory Animals. Ames, IA: The Iowa State Univeristy Press; 1973:72-5.
- Gardiner C, Fayer R, Dubey J. An Atlas of Protozoan Parasites in Animal Tissues. Washington, DC: American Registry of Pathology; 1998:67-8.
- Strait K, Else JG, Eberhard ML. Parasitic diseases of nonhuman primates. In: Abee CR, Mansfield K, Tardif S, Morris T, eds. Nonhuman Primates in Biomedical Research: Diseases. Vol 2. San Diego, CA: Academic Press; 2012:216-218.