A fatal epizootic of undetermined etiology in new world monkeys.

A peracute epizootic disease, strikingly characterized by profuse terminal hemorrhaging from the lungs, caused the deaths of 104 squirrel monkeys and 3 capuchin monkeys over a 22-month period. The case fatality rate was 100%. The pulmonary hemorrhaging was often accompanied by pulmonary edema and congestion, interstitial pneumonia, and hydrothorax. Additional histologic lesions included interstitial nephritis, hepatitis and hepatic necrosis, adrenalitis and adrenal necrosis, myocarditis, splenic atrophy or hypoplasia, pancreatitis and pancreatic necrosis, sialoadenitis, and encephalitis. Macaques maintained under identical conditions were clinically unaffected by the epizootic. There was an incidental relationship with contamination of feed, water, and housing facilities by excrement from feral Norway rats and cockroaches. Due to the association of the disease outbreak with abundant rodent and cockroach populations, and because the histologic features of the disease were suggestive of a viral etiology, encephalomyocarditis virus infection was implicated. However, histopathologic examinations of tissues from 68 monkeys; electron-microscopic studies on five monkeys; bacteriologic culturing; virus isolation attempts from 10 monkeys, rats, and cockroaches; and experimental inoculation studies in mice and squirrel monkeys all failed to reveal the causative agent, to provide a definitive diagnosis, or to reproduce the disease.