Metastasizing adenocarcinoma of the cecum in a squirrel monkey (Saimiri sciureus).

Abstract

perinodal connective tissue, and the lymphatics were occluded by epithelioid cell aggregates. There was a multifocal, mild to moderate, mixed inflammatory cell infiltration in the liver and lung. The cells included epithelioid cells and occasional multinucleated giant cells. Both cell types had very few acid-fast bacteria in their cytoplasm. No specific lesions were seen in the kidney, spleen, or heart. M. avium serotype 1 was isolated from the jejunal contents. This case of granulomatous enteritis caused by M. avium in a pig is unusual, both in terms of severity and the location of the main lesion. It is generally believed that infection with M. avium usually starts in the lymphoid tissues of the pharynx and/or in the small intestine and from there can spread to different organs, especially to the mesenteric lymph nodes.? In rare instances macro- and/or microscopic lesions are seen in the intestine, but these are believed to disappear early in the course of the disease and are in any case probably often o~erlooked.~ These intestinal lesions tend to localize in the Peyer’s patches and consist of microgranulomas.’ In other organs, especially lymph nodes, the bacteria usually cause a diffuse proliferation of epithelioid cells that contain acid-fast ba~teria.~.~ The histological picture is, however, not diagnostic for the type of mycobacterial infection. and therefore bacterial isolation is necessary.5 The mechanism behind mycobacterial infection has not been fully determined, but cell-mediated immunity and the activation of mononuclear macrophages are important in protection of the host.25 When lesions or clinical disease occurs due to mycobacterial infection, it is usually in an immunologically compromised host.* The clinical presentation and particularly the morphologic characteristics of the lesions seen in this case resemble those seen in ruminants infected with M. paratuberculosis. This bacterium is antigenically related to other species of mycobacteria, in particular M. avium.’ Pigs are susceptible to M. paratuberculosis infection, as has been reported from experimental studies and natural infections, but lesions are limited to the mesenteric lymph nodes.’ A vast majority of M. avium infections in pigs are ali~nentary.~ Because the lesions in this animal were most pronounced in the intestine and mesenteric lymph nodes, a peroral route of infection is most likely. The bacteria is a saprophyte and widespread in the surroundings. The source of infection is therefore often difficult to determine and remains unknown in this case. The pig came from a farm where there were no specific management or disease problems. No tuberculoid lesions have been registered in slaughtered animals from the farm. Since the diagnosis of M. avium infection, an intradermal skin test, with both avian and bovine tuberculin, was performed on the 19 sows on the farm. Two sows had a positive reaction to both types oftuberculin, while the other 17 were negative. It is uncertain whether these two sows were truly infected or not. One is still clinically healthy, and the other one was slaughtered shortly after the testing without any further examination. It can be concluded that M. avium infection, which usually is asymptomatic, can, on a rare occasion, cause a severe disease in pigs, with granulomatous inflammation in the intestine leading to chronic diarrhea and wasting.