Researchers have identified a highly aggressive strain of HIV in Cuba, which results from a DNA recombination event that is selected for based on the host’s genetic background. The aggressive recombinant HIV strain evolved in humans with high levels of RANTES,. RANTES is a protein made by humans that binds to the human CCR5 protein receptor, the preferred co receptor for HIV. By binding to the CCR5 receptor, RANTS blocks HIV entry into human cells. But the new recombinant HIV strain has evolved a method by which to enter human cells using an alternative receptor. Normally this transition take years which is why those that are HIV+ can live long lives without developing AIDS, however, in this scenario the high levels of RANTES selects for strains that have undergone ANTIGENIC SHIFT, creating a protease enzyme that allows for the synthesis of HIV proteins that can bind to the alternative human CRX4 receptor. This is a perfect example of CO-EVOLUTION and presents a new health challenge. See news source