I hate my computer. I had a huge post about this, and then it logged me out, thus.. Not posting it. Oh well, i'll write it out all over again :)
hiv (human immunodeficency virus) is the virus that causes aids (auto immunodeficency syndrom). Hiv is an std (sexually transmitted disease). Some other common std's are herpes and syphillus.
Std's are spready by sexual contact of one infected partner with another partner, when the sexual fluids of one partner (like semen, precum, vaginal fluids and sometimes blood) come in contact with the bloodstream of the other partner, through cuts in the anus, vagina, rare lacerations on the penis or testicles, or through the foreskin. Also, the skin of the anus and vagina is extremely absorbent on it's own, so a cut might not even be necessary.
It is true that it is much harder for a woman to give an std to a man through vaginal or anal sex. In the same way, it is hard for the partner receiving anal sex to give an std to his/her partner.
Hiv is spread like any other std. Here's how it can happen in relation to anal sex. The skin inside of the anus is very delicate, and it rips easily, which is a direct path to the person's bloodstream. If the man giving anal sex orgasms inside of his partner (male or female) and the anus has rips, then the semen (which contains some of the std) can come into direct contact with the bloodstream, thus transmitting the std. Plus, the anus is extremely absorbent, so even if there aren't rips, the disease may still be transmited.
Condoms are the only safe way to protect against std's. They keep the male's semen from coming in contact with the vagina or the anus, and they prevent vaginal fluids or blood from the vagina or anus from coming in contact with his penis. There is also protection for lesbians called a dental dam, but that's not relevant to this discussion of anal sex.
Plus, condoms are effective at preventing pregnancy, though with anal sex, the likelyhood of a male impregnating a female is very small.
I hope this has been informative!
