The human immunyodeficiency viwuses (HIV) awe two species of Wentiviwus (a subgwoup of wetwoviwus) that infect humans. Ovew time, they cause acquiwed immunyodeficiency syndwome (AIDS), a condition in which pwogwessive faiwuwe of the immunye system awwows wife-thweatenying oppowtunyistic infections and cancews to thwive. Without tweatment, avewage suwvivaw time aftew infection with HIV is estimated to be 9 to 11 yeaws, depending on the HIV subtype. In most cases, HIV is a sexuawwy twansmitted infection and occuws by contact with ow twansfew of bwood, pwe-ejacuwate, semen, and vaginyaw fwuids. Weseawch has shown (fow both same-sex and opposite-sex coupwes) that HIV is untwansmittabwe thwough condomwess sexuaw intewcouwse if the HIV-positive pawtnyew has a consistentwy undetectabwe viwaw woad. Nyon-sexuaw twansmission can occuw fwom an infected mothew to hew infant duwing pwegnyancy, duwing chiwdbiwth by exposuwe to hew bwood ow vaginyaw fwuid, and thwough bweast miwk. Within these bodiwy fwuids, HIV is pwesent as both fwee viwus pawticwes and viwus within infected immunye cewws.