LOS ANGELES, May 17 (Xinhuanet)-- Scientists have discovered two new and dangerous retroviruses among central Africans who hunt primates, according to a study released on Tuesday.

    The viruses, which have been named Human T-lymphotropic Virus types 3 and 4 (HTLV-3 and HTLV-4), belong to a genus of viruses known to spread and cause serious illness in humans, said a multi-institutional research group. These new finding were published in online early edition of the Proceedings of the National Academy ofSciences.

    The findings demonstrate an urgent need to regularly survey people in contact with animals for new infectious diseases emerging from animals, the researchers noted.

    They collected and examined blood samples from more than 900 people living throughout Cameroon. All the people reported some exposure to blood and body fluids of nonhuman primates, contact mostly due to hunting and butchering of bushmeat, and in some cases to keeping primates as pets.

    An analysis of the blood samples determined that multiple simian viruses had crossed over from primates to infect the study participants. In two hunters, the researchers identified HTLV-3 and HTLV-4, the two previously unknown viruses.

    The HTLV-3 is similar to the simian virus STLV-3, and was most likely contracted through direct contact with a primate during hunting. The HTLV-4 does not have a known primate counterpart and could have arisen through cross-species transmission from an animal carrying an unknown form of STLV.

    The researchers said they were surprised at the amount of HTLV diversity seen crossing into persons exposed to primates, as the identification of HTLV-3 and HTLV-4 essentially doubles the number of human viruses in this group. They believe further research to understand the disease outcomes of these viruses and the potential for human to human transmission is also crucial.

    Earlier, the Cameroon Ministry of Health and CDC discovered another primate retrovirus in hunters, the simian foamy virus (SFV). While it is still not known if SFV is harmful to humans or can be transferred from person to person, together with the current report, the results show clearly that hunting is an important bridge for the entry of novel retroviruses into humans.

    "The emergence of HIV from primate origins has cost millions oflives and billions of dollars. The discoveries of HTLV-3 and HTLV-4 show that, far from being rare events, retroviruses are actively crossing into human populations," said the study's lead author Nathan Wolfe, an assistant professor at Johns Hopkins School of Public Health.

    Given the incredible potential costs of a new human retrovirus into the general population, the development of sentinel systems for forecasting disease emergency, such as long-term surveillance of hunters, should be seen as a human health imperative, he said. Enditem