Almost lost my coffee: > Every time a new person is infected with (e.g.) HIV, from an epidemiological perspective, that increases the chances of some copy of t

Almost lost my coffee: > Every time a new person is infected with (e.g.) HIV, from an epidemiological perspective, that increases the chances of some copy of the virus in some person mutating into a virulent - even airborne - version More virulent, sure I'll grant that. But airborne?! HIV is in the Lentivirus family of Retroviridae. They're slow to reproduce, and airborne viruses need to be expelling many viral particles into the air to transmit. Additionally-- from where would HIV aerosolize? The only airborne retrovirus that I came across is Jaagsiekte, and it's benefited by that because it specifically targets the lungs. http://en.wikipedia.org/wiki/Jaagsiekte_sheep_retrovirus http://en.wikipedia.org/wiki/Jaagsiekte_sheep_retrovirus HIV already has lower transmission rates in genital->throat scenarios. It has too many evolutionary hurdles to become an airborne virus. If HIV does oneday become airborne it's morphology would look so different that we'd classify it as something else. Rhinoviruses (the virus that causes the common cold) are easily aerosolized because they're tiny and are in a protein capsid. Sorry, that was maybe an overkill explanation, and the core of your statement ("more virulent") is correct. It just triggered some nerding out :D