| All mammals have within their genetic makeup leftover traces of past virus infections, especially those with the retrovirus family of viruses. These viruses are special in that part of their replication strategy is to put their genome into the host (the cell which they have infected) cell's chromosomes. If this occurs in cells used for reproduction, then the virus becomes fixed as part of the host's genetic makeup and does not need to replicate itself; these are called endogenous retroviruses. There are other retroviruses which have to infect new host animals, replicate and produce progeny to continue to survive (e.g. HIV) and these are called exogenous retroviruses. There is no clear link with disease caused by endogenous retroviruses but exogenous retroviruses do cause many important human and veterinary diseases. Work done in humans has indicated a potential role for human endogenous retroviruses (HERV) in a broad range of pathology and autoimmune disease. |