Species: Monkey Strain/breeder: Rhesus macaque (Macaca mulatta) Sex: Male Age: 6 years Study type: Infection Treatment: SIV-Infection Animal status: Euthanized due to progressive immunodeficiency Clinical findings: Pneumocystis carinii pneumonia, chronic-active gastroenteritis Organ: Skin, skeletal muscle, diaphragm Macroscopic finding(s): No abnormalities detected in either organ Staining: H&E Literature: Frenkel JK (1997) In: Connor DH, Chandler FW, Schwartz DA, Manz HJ, Lack EE (eds) Pathology of infectious diseases. Stamford CT, Appleton and Lange, pp 1253-1259 Karr SL, Wong MM (1975) A survey of Sarcocystis in nonhuman primates. Lab Anim Sci 25: 641-645 Lane JH, Mansfield KG, Jackson LR, Diters RW, Lin KC, MacKey JJ, Sasseville VG (1998) Acute fulminant sarcocystosis in a captive-born rhesus macaque. Vet Pathol 35: 499-505 Levine ND (1986) The taxonomy of Sarcocystis (Protozoa, Apicomplexa) species. J Parasitol 72: 372-382 Mandour AM(1969) Sarcocystis nesbitti n. sp. From the rhesus monkey. J Protozool 16: 353-354 Mehlhorn H, Heydorn AO, Janitschke K (1977) Light and electron microscopical study on sarcocysts from muscles of the rhesus monkey (Macaca mulatta), Baboon (Papio cynocephalus) and Tamarin (Saguinus(=Oedipomidas) oedipus). Z Parasitenkd 51: 165-178

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Abstract

Aim of the study
In this case report we describe the appearance of sarcocystosis in an SIV-infected rhesus macaque (Macaca mulatta).

Materials & methods
The animal was euthanized 25 weeks after SIV infection. Representative tissues were fixed in formalin, embedded in paraffin and stained with H&E.

Results
Apart from severe alterations in various organs due to opportunistic infections, the skeletal muscles appeared to be normal. In histology, the skin, skeletal muscles and the diaphragm were shown to contain numerous protozoic tissue cysts within remaining muscle fibres, with the fibres adjacent to the cyst's surface. The cysts were lined by a thick eosinophilic wall with long, regularly arranged, perpendicular cross striations. They contained large numbers of basophilic banana-shaped metrocytes and/or bradyzoites. The interstitial inflammatory reaction was mild and focal host reaction around parasitic cysts together with invading inflammatory cells could be seen. Multinucleated muscle cells indicating muscle regeneration were located next to the tissue cysts and inflammatory infiltrate, which consisted of lymphohistiocytic cells and mast cells accompanied by eosinophilic granulocytes.

Conclusions
With regard to the structure of the parasitic cysts, the shape of the metrocytes and the morphology of the cyst wall, we suspect Sarcocystis kortei to be the etiologic agent. Since infection with Sarcocystis spp. without contact to an intermediate host is not described in rhesus monkeys, the infection of this animal must have taken place before the onset of experiment. The number of sarcocysts and the amount of inflammatory response are of interest in this case, but the morphology of the cyst walls indicates maturity. It has to be considered that the inflammatory reaction is due to rupture of tissue cysts and the progressive failure of the immune system.