New York, Aug 21 (IANS): Viruses closely related to human immunodeficiency virus (HIV) that may cause AIDS have infected primates in Africa for as long as 16 million years, says a new study.

"Lentiviruses closely related to modern SIVs (simian immunodeficiency virus) were present in Africa and infecting the ancestors of cercopithecine primates as far back as 16 million years ago,” the study noted.

Interested in the history of lentiviruses--the group of retroviruses to which HIV and its simian (monkey) relatives, the SIVs belong--Welkin Johnson, from Boston College, US, and colleagues studied the evolution of on an antiviral gene called TRIM5 in African monkeys.

TRIM5 is part of a group of antiviral genes called "restriction factors," which have evolved to protect host cells from infection by viruses.

The human version of TRIM5 does not interfere with--and therefore not protect against--HIV, but many monkeys have TRIM5 variants that do render HIV harmless and are therefore immune to HIV/AIDS, the study said.

The findings appeared in the journal PLOS Pathogens.