A Planet of Viruses - Carl Zimmer [21]
Little did they know that they were publishing the first observations of what would become the greatest epidemic in modern history. The five Los Angeles men did indeed have a cellular-immune dysfunction, one that would turn out to be caused by a virus known today as human immunodeficiency virus (HIV). The virus, researchers would later discover, had been secretly infecting victims for fifty years. During the 1980s it finally exploded, and since then it has infected sixty million people. It has killed nearly half of them.
HIV’s death toll is all the more terrifying because it’s actually not all that easy to catch. You can’t get HIV if an infected person sneezes near you or shakes your hand. HIV has to be spread through certain bodily fluids, such as blood and semen. Unprotected sex can transmit the virus. Contaminated blood supplies can infect people through transfusions. Infected mothers can pass HIV to their unborn children. Many people who take heroin and other drugs have acquired HIV if they’ve shared needles with infected users.
Once HIV gets into a person’s body, it boldly attacks the immune system itself. It grabs onto certain kinds of immune cells known as CD4 T cells and fuses their membranes like a pair of colliding soap bubbles. Like other retroviruses, it inserts its genetic material into the cell’s own genome. Its genes and proteins manipulate then take over the cell, causing it to make new copies of HIV, which escape and can infect other cells.
At first, the population of HIV in a person’s body explodes rapidly. Once the immune system recognizes infected cells it starts to kill them, driving the virus’s population down. To the infected person, the battle feels like a mild flu. The immune system manages to exterminate most of the HIV, but a small fraction of the viruses manages to survive by lying low. The CD4 T cells in which they hid continued grow and divide. From time to time, an infected CD4 T cell wakes up and fires a blast of viruses that infect new cells. The immune system attacks these new waves, but over time it becomes exhausted and collapses.
It may take only a year for an immune system to fail, or more than twenty. But no matter how long it takes, the outcome is the same: people can no longer defend themselves against diseases that would never be able to harm a person with a healthy immune system. In the early 1980s, a wave of HIV-infected people began to come to hospitals with strange diseases like pneumocystis pneumonia.
Doctors discovered the effects of HIV before they discovered the virus, dubbing it acquired immunodeficiency syndrome, or AIDS. In 1983, two years after the first AIDS patients came to light, French scientists isolated HIV from a patient with AIDS for the first time. More research firmly established HIV as the cause of AIDS. Meanwhile, doctors were discovering more cases of AIDS, both in the United States and abroad. Other great scourges, such as malaria and tuberculosis, are ancient enemies, which had been killing people for thousands of years. Yet HIV went from utter obscurity in 1980 to a global scourge in a matter of a few years. Here was an epidemiological mystery.
To solve it, scientists began to sequence the genes of HIV they isolated from different patients. They examined HIV not just from the United States but from other countries around the world where it was beginning to spread as well. They drew evolutionary trees, with each strain of HIV a branch sprouting from a common ancestor. Researchers