Histologic lesions in cynomolgus monkeys (Macaca fascicularis) naturally infected with simian retrovirus type D: Comparison of seropositive, virus-positive, and uninfected animals

Simian retrovirus (SRV) type D is a common cause of simian acquired immunod eficiency syndrome (SAIDS), a usually fatal immunosuppressive disease of ma caques. Associated grass and histologic lesions have been well described fo r the rhesus macaque (Macaca mulatta) in experimental and natural infection s. However, morphologic changes induced by this virus at the gross and ligh t-microscopic level have not been documented in the cynomolgus macaque (Mac aca fascicularis). In 1996, sporadic cases of anemia, weight loss, and diar rhea were noted in a colony of cynomolgus macaques in our research facility . Out of 28 animals. 24 tested positive for SRV by serology or virus isolat ion. Animals could mainly be classified into 1 of 2 categories: 1) positive for virus isolation but negative for SRV antibody and 2) negative for viru s isolation but antibody positive. During the process of eliminating the vi rus from the colony, a complete postmortem examination was performed on the 24 infected animals that had to be culled. Twelve SRV-negative animals wer e available as controls. Minimal to mild follicular lymphoid infiltrates we re seen in various organ systems in 75% of the negative animals, compared w ith moderate to marked infiltrates in 83% of infected animals. Lymphoid inf iltrates were more common in the brain. bone marrow, and salivary gland of viremic animals and were rare to nonexistent in seropositive or negative an imals. Lymphoid hyperplasia was present in 38% of the infected animals, whe reas lymphoid depletion was seen in 47% of the infected animals. Overall, l esions were of greater severity in viremic animals than in virus-negative o r seropositive animals. Overall, infected animals had lower. statistically significant hematocrit and lymphocyte values. Viremic animals had significa ntly lower hematocrit. white blood cell, lymphocyte, and neutrophil values than did controls. Only 1 out of 24 infected animals had clinical signs tha t were consistent with the definition of SAIDS, and none had evidence of op portunistic infections. Lesions were similar to those already reported in o ther species of macaques, but the absence of severe illness that was consis tent with SAIBS in most viremic animals suggests that there may be a differ ent manifestation of disease in the cynomolgus.