Scientists believe that HIV has existed since the early 1950s, if not earlier; a scattering of plasma and tissue samples (from an African, an American, and a Norweigian) shows that it infected at least some people before AIDS became a pandemic. What made the virus so virulent? What changed? Well, HIV is terrifically prone to mutation, so it’s possible that the forms that existed before the 1970s were just less easily transmissible. But it seems more like the modern world makes us more vulnerable — ignoring whether behavioral patterns changed (through increased casual sex or increased use of IV drugs), the formation of a more efficient blood bank system and hugely increased intra- and international travel made it much more easy for the HIV virus to travel. I don’t see this trend going away; just as political and economic instability halfway around the globe can now effect the United States virtually immediately, medical crises are not always going to stay regional in a more interconnected world. In 2000, an estimated 2.4 million sub-Saharan Africans died of AIDS; an estimated 780,000 South and Southeast Asians died; an estimated 5 million people were newly infected with HIV this year. I’m fortunate that no one close to me has acquired AIDS, although friends and relatives of friends and relatives have died, and in the United States, we’ve done a largely masterful job of limiting the transmission of HIV and helping HIV-positive people live longer and more healthy lives; still, I don’t think we’re going to be able to ignore the spread of AIDS outside our borders forever. (Links via MetaFilter‘s day of participation in Link and Think, a weblog project for World AIDS Day, and communication with AIDS-researching MeFilistine Sennoma.) None