National Geographic : 1994 Jul
strike, infecting and disabling the immune sys tem's critical T cells. They realized also that HIV is relatively fragile and cannot survive long outside the body. Therefore, HIV infects new hosts through bodily fluids-primarily blood and semen. "Initially AIDS looks much like any other infection," explained Anthony Fauci. "HIV is readily detected in the blood. Very quickly the immune system begins producing antibod ies to neutralize the virus. Six months later it may be all but impossible to find the virus itself in the bloodstream." Antibodies to the virus persist; their pres ence is what AIDS-testing detects. The virus, however, is hiding. Where? Fauci showed me a magnified cross section of a lymph node from one of his patients. Pea size nodules scattered throughout the body, lymph nodes normally act as filters, trapping viruses so that immune cells can detect and destroy them. During certain illnesses lymph nodes grow crowded with infection-fighting T and B cells. Then we call them swollen glands. A lymph node-the lion's den of the immune system-would seem the last place a virus should hide. But the lymph node from Fauci's patient was speckled with tiny black dots: AIDS viruses. Somehow, perhaps by con cealing themselves in a coating of substances that the immune system itself makes, HIV incubates safely in the lymph nodes for years. Eventually the viruses multiply. Then, bloated with HIV, lymph nodes deteriorate, spilling viruses into the bloodstream. After that the host's immune cells face a far more confounding enemy. AIDS researchers have learned that HIV mutates as it copies itself, creating an army of variant strains within each infected person. No longer one beast but ten thousand, AIDS viruses now have an unassailable advantage. The immune system must create a new and different contingent of T cells to battle every new viral strain. Meanwhile, all AIDS viruses can attack and destroy critical T cells. "Eventually," said biologist Robert May of Oxford University, "so many different preda tors simply overwhelm the immune system." How DO RESEARCHERS keep track of the huge, evolving menagerie of different AIDS viruses? At the Los Alamos National Laboratory in New Mexico, molecu lar geneticist Gerald Myers oversees the world's largest data bank of molecular infor mation about HIV. As I visited him at the lab's HIV Sequence Database and Analysis Unit, the newest addition was arriving. It was not a biological specimen. Rather it streamed across a computer monitor as a long string of num bers and letters. Myers was downloading information from England about the strain that may have killed the 25-year-old British sailor in 1959. The virus would be preserved on a computer disk as a sequence of chemical codes that describe the makeup of its genes. Myers showed me catalogs with hundreds of pages of coded sequences of the various viruses in his collection. HIV has been broken into types, subtypes, and strains. The primary AIDS virus is a type called HIV-1. To date, scientists have detected at least seven major subtypes and thousands of strains. Research ers also have identified another type of the virus, called HIV-2, which usually causes a less severe form of the disease. Nightmare in the making * A long evening lies ahead for women who work the brothels of Bombay, a center of India's AIDS explosion (right). Though some now insist on condom use, half the city's 100,000 sex workers have already been infected. Even with rampant warts (top), caused by a papilloma virus, an HIV-weakened worker finds clients. Professional blood donors and lax medical procedures also spread HIV. "We need to fight this as a national emer gency, not a mere health problem," says Bombay doctor Ishwar Gilada, who treats and counsels sex workers.