Living with a million-year long infection

Despite eliciting host immunity, several viruses establish chronic, often life-long infection in humans that can affect immune function. The ultimate form of parasitism and evasion of host immunity is for the virus genome to enter the germline of the host. Retroviruses have invaded the host germline on the grandest scale, and this is evident in the extraordinary abundance of endogenous retroelements in the genome of all vertebrate species that have been examined.

Recent studies suggests that such viral endogenisation events continue to shape host immunity and other physiological systems over long evolutionary times and through diverse mechanisms. Some acquire novel function that provides a host fitness advantage, a process known as exaptation. Although recent integrations may be more detrimental to host physiology or immunity, evidence will be presented that integrations acquired millions of years ago were positively selected and continue to shape host physiological and pathological processes in humans.