Serological and histological studies on adult rabbits with recent, naturally acquired encephalitozoonosis.

Twenty adult rabbits were killed two to 12 weeks after antibodies to Encephalitozoon cuniculi were first detected in their sera. Specimens of urine were examined for E cuniculi and sections of kidneys and brains were examined both for organisms and lesions consistent with encephalitozoonosis. Organisms were observed in the kidneys from two weeks after the appearance of antibodies, and histological lesions in the kidneys were observed after five weeks. However, organisms were rarely seen in the brain and lesions in this organ were infrequent and, generally, not present until at least eight weeks after the first detectable antibody. The results indicate the course of natural infection of encephalitozoonosis in rabbits and show that serology is the most sensitive procedure for its early diagnosis.