Mesenchymal neoplasms associated with type D retroviruses in macaques

The type D subfamily of retroviruses contains five distinct viruses which are found in New and Old World monkeys. The retroviruses found in Old World macaque (genus Macaca) monkeys are exogenous to the species and upon injection induce a fatal simian acquired immune deficiency syndrome (SAIDS). Two serotypes of type D virus, SAIDS retrovirus types 1 and 2 (SRV-1 and SRV-2), are found in captive macaques in primate centres in the United States. In addition to SAIDS, two neoplasms, retroperitoneal fibromatosis (RF) and subcutaneous fibrosarcomas (SF), have been found in macaques with type D retrovirus-induced SAIDS. Only SRV-2 is found in association with RF, and only about 35% of SRV-2-infected macaques develop RF. SF is found in association with both serotypes, but less than 5% of infected monkeys develop SF. The RF in macaques is potentially a model for human disease since the lesions in macaques are similar to the idiopathic RF described in humans. Thus far, RF has not been found in species other than macaque or man. The complete sequence of three type D retroviruses is known. Importantly, no oncogenes are present in the viral genome. Therefore, the mechanisms for tumour induction which involve immunosuppressive or genetic properties of the virus that are distinct from classic oncogenes must be considered.