Ok, there are many ways through which a person (male or female) can contact HIV AIDS. Drug users sharing "dirty" (or shared) neeldes run the highest risk. It takes also only ONE drop of infected blood to transmit that disease. So, also you have in the porn industry "actors" who will get paid higher fees if they accept to go "bareback" (no protection, no condom), thus a very very high risk of getting or spreading this disease (and some people even have it and don't know that they do....).
Consider also that the anus is not a vagina: its sides are pretty much like scissors. They cut. Which is why condoms are also suggested (with water-based gell....no oïl: oïl will help perforate)..
And, of course, the anus does not return to a normal closure after sex. And while some people get used to ever bigger "thrills" with bigger sex toys...and go even to what is known as "fist-fucking", then you end up with people (man and women) who must wear adult diapers at a relatively Young age................So be careful indeed,