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Contributor Comment:  
In fish, Spironucleus salmonicida causes significant mortality in farmed salmon(10). Spironucleus vortexes is a fresh water species that causes disease in the ornamental fish industry and is highly suspected to be one of the potential causative agents of hole-in-the-head disease in cichlids(5,11). In birds, Spironucleus meleagridis was first isolated from turkeys and described and named by McNeil, Hinsha and Kofoid in 1941 but was later found to infect many species of birds(5,9,14). Infection with Spironucleus meleagridis is reported to cause infectious catarrhal enteritis in turkeys and other fowl including Chukar partridges and ring-necked pheasants and is also associated with significant morbidity and mortality(5). Cysts of S. meleagridis are found most frequently in thick mucus and are less frequently found in feces. This mechanism may enhance transmission and survival of the organism in the environment(14).Â
In laboratory rodents, Spironucleus muris (and potentially other Spironucleus species) is a commensal organism of the small intestine of rats, mice, and hamsters but can cause significant disease in immunocompromised animals (i.e. disease, environmental stress, very young animals). In severe outbreaks, there can be up to 50% mortality particularly in young mice that clinically have depression, diarrhea, and weight loss. The organism primarily colonizes the duodenal crypts and may cause an acute or chronic form of disease(12).
In non-human primates, a flagellated organism (Octomitus pithily) was described in the feces of nonhuman primates as early as 1929 by DaCunha and Muniz(6). More recently, phylogenetic analysis was performed on an unknown diplomonad isolated from two rhesus macaques immunocompromised from simian acquired immune deficiency syndrome (SAIDS). The organism was most closely related to Spironucleus meleagridis. Further investigation and screening of both SIV infected and uninfected rhesus macaques revealed that the organism was prevalent in the colony and most likely a commensal organism in normal macaques. It is suspected that the organism invades the colonic mucosa in immunocompromised animals, striking the gastrointestinal associated lymphatic tissue and disseminating either to regional lymph nodes or systemically via the lymphatics or vasculature(1). We suspect that in the present case, the abscess originated in a colonic lymph node following invasion from the colon. Lesions associated with Spironucleus were not seen in other tissues.
The bacteria noted along the epithelial border are consistent with Brachyspira sp. (B. pilsicoli is the most common). This is a common, often incidental finding in the large intestine of macaque species. The role that this bacterium plays in colonic inflammation is currently unknown; however, since it can be found in the colon of almost all macaque species, its role in causing disease is likely negligible.
JPC Diagnosis:  
Conference Comment:  
In SIV-infected monkeys, lymphadenopathy and splenomegaly due to lymphoid hyperplasia is present in early stages of disease with lymphoid atrophy (depletion) in later stages, and thymic atrophy occurs in young animals. Histologically, there is giant cell (syncitial) interstitial pneumonia, granulomatous and giant cell lymphadenitis and splenitis, giant cell meningoencephalomyelitis, non-septic vegetative valvular endocarditis, glomerulosclerosis, and syncitial giant cells may also be present in lymph nodes, kidney, and the gastrointestinal tract(2,3).
Other lentiviruses of veterinary importance include equine infectious anemia virus in horses, Maedi-visna virus which produces ovine progressive pneumonia in sheep, caprine arthritis-encephalitis virus in goats, feline immunodeficiency virus in wild and domestic felids, and bovine immunodeficiency-like virus in cattle(4).
References:
2. Barry P, Martinas M, Lerche M, McChesney MB, Miller CJ. Virology research. In: Wolfe-Coote S, ed. The Laboratory Primate. San Diego, CA: Elsevier Academic Press; 2005:565-569.
3. Baskin GB. Pathology of nonhuman primates. In: Pathology of Laboratory Animals, 49th conference, Armed Forces Institute, 2005.
4. Campbell RSF and Robinson WF. The comparative pathology of the lentiviruses. J Comp Pathol. 1998;119(4):348-352.
5. Cooper GL, Charlton BR, Bickford AA, Nordhausen R: Hexamita meleagridis (Spironucleus meleagridis) infection in chukar partridges associated with high mortality and intracellular trophozoites. Avian Dis 48: 706-710, 2004
6. da Cunah A MJ: Nota sobre os parasitas intstinaes do Macacus rhesus con a descripcao de uma nova especie de octomitus. Mem Inst Oswaldo Cruz 5: 34-35 1929
7. Gardiner CH FR, Dubey JP: An Atlas of Protozoan Parasites in Animal Tissues, 2 ed. Armed Forces Institute of Pathology, Washington DC1998
8. Jorgensen A, Sterud E: Phylogeny of spironucleus (eopharyngia: diplomonadida: hexamitinae). Protist 158: 247-254, 2007
9. McNeil E HW, Kofoid CA: Hexamita Meleagridis Sp. Nov. from the Turkey. American Journal of Epidemiology 34 Section C(2): 71-82, 1941
10. Millet CO, Lloyd D, Williams C, Williams D, Evans G, Saunders RA, Cable J: Effect of garlic and allium-derived products on the growth and metabolism of Spironucleus vortens. Exp Parasitol 127: 490-499, 2011
11. Paull GC MR: Spironucleus vortens, a possible cause of hole-in-the-head disease in cichlids. Diseases of Aquatic Organisms 45: 197-202, 2001
12. Percy DH BS: Pathology of Laboratory Rodents and Rabbits, 3 ed. Blackwell Publishing, Ames, Iowa, 2007
13. Wenrich D: A Species of Hexamita (Protozoa, Flagellata) from the Intestine of a Monkey (Macacus rhesus). The Journal of Parasitology 19: 225-229, 1933
14. Wood AM, Smith HV: Spironucleosis (Hexamitiasis, Hexamitosis) in the ring-necked pheasant (Phasianus colchicus): detection of cysts and description of Spironucleus meleagridis in stained smears. Avian Dis 49: 138-143, 2005