Chronic Interstitial Myocarditis in Primates

Chronic interstitial myocarditis is a frequent disease of primate hearts. It is of uncertain clinical importance and unknown cause [3. 41. In recent toxicological studies conducted at Bio-Research Laboratories. 3 I2 hearts from squirrel (Saimiri sciureus), cynomolgus (Macaca fascicularis). rhesus (Maraca mularra) and assam (Maraca assamensis) monkeys were examined. The incidence of chronic interstitial myocarditis is presented in table I. One hundred and six monkeys (34%). almost equally divided among males and females, had this condition. Others have reported an incidence from 2% [I] to 50% [6]. One author [2] reported a higher incidence of myocarditis in females ( 13%) than males (5%) in howler monkeys (Alouarra caraya). Hearts examined after necropsy did not have gross abnormalities and their weights were within the normal range for the species. Histological lesions were similar to those described by others [3, 61. There were focal random collections of lymphocytes. mononuclear cells, plasma cells and sometimes eosinophils in myocardial fibers or perivascular locations or both. Myocardial necrosis was not constant. but when present, was slight. There was inflammation of myocardium of all chambers of the heart, as well as the interventricular septum. Bacteria, viral inclusions or parasites were not seen near the lesions. Certain bacteria and viruses have been ruled out because no neutralizing antibodies were detected in the sera of monkeys given these agents experimentally [5]. Perhaps the condition is caused and precipitated by stress because it was less severe in monkeys rested for 12 to 14 weeks after capture than in those rested for 6 weeks [5].