Retroviruses: ancient and modern

Retroviruses are transmitted in two distinct ways: as infectious virions an d as 'endogenous' proviral DNA integrated in the germ line of their hosts. Modern infectious viruses such as HIV recently infected mankind from simian hosts, whereas human endogenous retroviral genomes have been present throu ghout old world primate evolution. Recently we have characterised novel ret roviruses in humans and pigs. Human retrovirus 5 (HRV-5) is detected as an exogenous genome in association with arthritis and systemic lupus erythemat osus. Porcine endogenous retroviruses (PERV) are carried in swine DNA but c an be activated to produce virions that are infectious for human cells, whi ch has implications for xenotransplantation. A brief account of HRV-5 and P ERV is given here.