HIV: if you can't beat them ...

HIV came out of the closet when I was in medical school. We followed it closely, back when it was a disorder of Haitians and hemophiliacs. The gay connection came later.

There's a lot been learned about its biology since then. For an old-timer this Loom article gives a flavor of what's current (emphases mine) ...

Learning To Ignore Your Viruses. The Loom: A blog about life, past and future:

In an opinion piece in PLOS Pathogens, Viktor Muller and Rob J. De Boer ... [show] the relationship of HIV-like viruses in apes and monkeys... HIV, marked in red, is not a single lineage of viruses. One form, HIV-2, jumped from sooty mangabey monkeys into people several times. The more common form, HIV-1, descends from chimpanzee viruses, which have moved into humans many more times. As the tree shows, lots of primates get infected by their own HIV relatives, and this appears to have been going on for millions of years. But if you look at sooty mangabeys or some other monkey, you generally find abundant amounts of the virus without any sign of an overactive immune system... The blue arrows on the tree mark the rise of new virus strains in macaques that came from sooty mangabeys. This shift appears to have happened at primate research centers in the past few decades. In their new hosts, these viruses cause lots of nasty symptoms.

Muller and De Boer propose an intriguing hypothesis to explain all of this: perhaps apes and monkeys don't suffer ill effects from these viruses because they carry copies of the viruses in their own genome. After all, the authors point out, HIV's genes have been isolated in human sperm DNA, so these viruses clearly have the potential to make their way into a host genome. Muller and De Boer suggest that primate viruses got into their hosts' genome. The young primates then began making proteins from the virus, which their developing immune system recognized as part of their 'self.' When the primates then got infected with new copies of the virus, they didn't mount an attack or become overstimulated. The viruses infected the primate's immune cells, but they were only a minor burden to the primates compared to a collapsed immune system...

...It's cool but a little frightening to imagine if Muller and De Boer are on to something. It would mean that primates have not survived their own HIV epidemics by destroying the virus. Nor would it mean that the virus had become more benevolent, in order to spare its host. It would mean that they simply evolved to ignore the virus altogether...

Invite them in. Give them food. Let them take what they want. Go about one's business. Didn't China do that with the invading Mongols?