A Planet of Viruses - Carl Zimmer [23]
All this evidence is now pointing to how HIV-1 got its start. HIV-1-like viruses had been circulating among populations of chimpanzees throughout Africa. Hunters sometimes killed chimpanzees for meat, and from time to time they became infected by the viruses. But these hunters, living in relative isolation, were a dead end for the viruses. In the early 1900s the opportunities for these viruses changed as colonial settlements in central Africa began to expand to cities of ten thousand people or more. Commerce along the rivers allowed pathogens to reach the cities from remote forests. The chimpanzees carrying viruses most closely related to HIV-1 live today in the jungles of southeast Cameroon. It may be no coincidence that the rivers of that region flow south and eventually reach Kinshasa.
In the growing city of Kinshasa (then known as Leopoldville), HIV-1 could multiply. Instead of a few dead ends, it found a population that could sustain it and inside of which it could evolve into new forms better adapted to humans. By 1960, HIV-1 had bloomed into a wide genetic diversity, although it probably only infected a few thousand people.
Worobey and his colleagues have started to map the subsequent spread of HIV-1 out from Kinshasa to the rest of the world. The most common strain of HIV in the United States, for example, is known as HIV-1 subtype B. The oldest lineages of HIV-1 subtype B are found in Haiti, and Worobey estimates they branched off from African strains in the 1960s. That happens to be a time when many Haitians who had been working in the Congo returned to their homeland after the country became independent from Belgium. They may have unwittingly brought HIV back to the New World with them. Haitian immigrants or American tourists may have then brought HIV to the United States. The oldest lineages of HIV-1 subtype B in the United States, Worobey and his colleagues found, date back to about 1970. That’s about four decades since the virus became established in humans, and about one decade before five men in Los Angeles became sick with a strange form of pneumonia.
By the time scientists recognized HIV in 1983, in other words, the virus had already begun to turn into a global catastrophe. As a result, HIV has had a huge head start on scientists who hope to halt its spread. It would not be until the early 1990s that some strategies began to show real promise for slowing the epidemic. Changing people’s behaviors has proven effective. Uganda launched a major campaign against HIV that featured condom use and other public health measures. As a result, the country reduced its HIV rate from about 15 percent in the early 1990s to about 5 percent in 2001. Unfortunately funding for these programs began to ebb after a few years, and the infection rate in Uganda has begun to rise again.
Other researchers have investigated medications that can slow the rise of HIV in infected people, so that their immune systems can remain strong enough to block the onset of AIDS. Millions of people now take a cocktail of drugs that interfere with the ability of HIV to infect immune cells and use them to replicate. In affluent countries like the United States, these drug therapies have allowed some people to enjoy a relatively healthy life. But the cost of these drugs has meant that most people with HIV—living in the poorest countries—cannot afford a treatment that might give them extra years or even decades of life. That’s beginning to change rapidly, as the United States and nongovernmental organizations are now starting to provide these drugs to the most afflicted countries and as treatment programs are starting to be scaled up dramatically.
Yet these drugs,