Fatal outbreaks of proliferative enteritis caused by Lawsonia intracellularis in young colony-raised rhesus macaques

Ten juvenile rhesus monkeys (Macaca mulatta) died acutely in two separate d isease outbreaks. The animals had segmental thickening of the distal ileum with associated proliferative, rugous appearing mucosae. Microscopically, n ecrosis, exudative inflammation, mucosal ulceration, and crypt hyperplasia were present. Intracellular organisms were seen histochemically and ultrast ructurally, and were confirmed to be Lawsonia intracellularis using a speci fic immunohistochemical method. Proliferative enteropathic conditions cause d by L. intracellularis are reported in an ever-increasing range of hosts, suggesting that the infection may exist unrecognized in an even greater arr ay of species, possibly including man.