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The factory is extraordinarily efficient. Research conducted by Harvard's Haseltine and published in the July issue of the journal Cell reveals that the virus has a unique genetic component that allows it to reproduce itself a thousand times as fast as any other kind of virus. The mechanism for this reproduction "is one of the biggest effects I've seen in biology," says Haseltine. "It helps explain why AIDS is such a devastating disease and why it can spread so fast." In the process of rampant replication, the AIDS virus destroys its home, the T cell. Thus it is a peculiar feature of this disease that as it progresses, the helper T cells disappear and so does the virus. By then, however, the patient is invariably beyond recovery.
But not everyone infected with the AIDS virus develops the deadly syndrome. Most develop a seemingly peaceful coexistence with the virus, says Dr. James Curran, who heads the CDC task force on AIDS. "They have no symptoms at all or very minimal symptoms, but they have persistent infection and are probably persistently infectious to others." Another group suffers a mild version of immune-system depression, with symptoms and signs that include malaise, weight loss, fevers and swollen lymph nodes. This syndrome, called AIDS-related complex, or ARC, sometimes but not always develops into full-blown AIDS.
Curran estimates that for each of the 12,000 cases of AIDS reported so far in the U.S., there are at least five to ten cases of ARC. Sample studies based on blood tests suggest that an additional 500,000 to 1 million Americans are symptomless carriers of the virus. What will happen to this group is the object of much speculation and study. "That's the million-dollar question," says Dr. Michael Lange of St. Luke's-Roosevelt Hospital in New York City. The guess is that 5% to 10% of people who do not have symptoms but do have antibodies to the virus (meaning they have been exposed) will develop AIDS within five years. There is no way to tell which ones will get it. "It's like Russian roulette with one bullet and ten chambers," says Ronald Sanders of the Los Angeles health department. For people with ARC, the odds of developing AIDS within three years may approach 20%, or two bullets.
Researchers are hunting for clues to why one person develops the disease while others merely harbor the virus. Some investigators suspect that additional viral infections may play a role as accomplices or triggers. The main suspects: Epstein-Barr virus and cytomegalovirus (both members of the herpes family) and the virus that causes hepatitis B. The difficulty, says Lange, comes in determining whether such viruses are in fact co-agents of AIDS or merely tagalong infections.
Scientists are also trying to learn more about how and when the disease is spread. Are there, for example, certain periods of time when a person is more infectious than others? Many answers will be found within the next year or so, predicts Curran. "We'll know the risk of a pregnant mother in delivering a healthy infant vs. an ill one or a stillborn. We'll be able to quantify those kinds of things."
Just how immediate a threat AIDS poses to heterosexuals is much debated. The fact is, nobody knows. "There is nothing about the biology of the virus to lead us to think anyone is immune solely on the basis of the type of sexual partner," says Volberding of San Francisco General. "Heterosexuals are clearly at risk of acquiring the disease from sexual contact." The Burk family of Cresson, Pa., is a sad case in point. Patrick, 27, a hemophiliac, contracted AIDS from a contaminated batch of blood-clotting factor, which he requires to control his condition. His wife Lauren, 24, has since developed ARC and apparently passed the virus on to their 15-month-old son Dwight, most likely during her pregnancy. Daughter Nicole, 4, is the only one in the family left untouched by the disease.