Medicine: AIDS Research Spurs New Interest in Some Ancient Enemies

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Latency is a characteristic common to all members of the troublesome herpes family. Herpes zoster, which causes chicken pox, sometimes hides in nerve cells, where no drug or antibody can reach it. Years after the pox attack, usually in middle or old age, zoster can sneak out and cause excruciating attacks of shingles. The Epstein-Barr virus, a herpes family member that causes infectious mononucleosis, follows a similar strategy, though its hiding place is not in the nerves but in the B cells, the very cells that make antibodies to viruses. In contrast to the dormant staying power of herpes viruses, the persistent hepatitis B virus can linger in the liver for decades while continuing to multiply. Those who are infected as infants, as many newborns in China, Southeast Asia and Africa are, almost always become lifelong carriers. "The virus doesn't do much damage for a long time," says Jesse Summers of the Fox Chase Cancer Center in Philadelphia, "but then, after 20 or 30 years, chronic liver problems develop." Papillomaviruses, which cause warts, may also take up permanent residence in the body, biding their time in skin cells.

Some DNA viruses become inactive and escape detection by the host's immune system by insinuating their genetic material into the DNA of the host cell. A retrovirus, however, must first use its enzyme called reverse transcriptase to convert its RNA into a DNA molecule, which can then insert itself into the cell's DNA and order the cellular machinery to begin producing more retroviruses. Or it can remain dormant and invisible to the immune system, / awaiting some signal to begin causing trouble. Hidden in the cell's DNA, says David Baltimore, who shared a Nobel Prize for the discovery of reverse transcriptase, the viruses "have found the perfect niche."

Many of these chronic viruses are now being linked to cancer. A landmark study conducted in Taiwan between 1975 and 1978 by Dr. R. Palmer Beasley, now at the University of California, San Francisco, found a striking connection between chronic hepatitis B infection and liver cancer, a leading killer in the Third World. "Someone infected with hepatitis B has 100 times the normal risk of developing liver cancer," says Beasley, "and that's being conservative." The Epstein-Barr virus has been associated with a couple of types of cancer. In Central Africa and New Guinea, it has been linked to Burkitt's lymphoma, an immune-cell cancer that primarily strikes children. In southern China, the virus plays a role in nasopharyngeal carcinoma, a malignancy of the nose and throat that afflicts more than 50,000 people a year. Retroviruses are known to cause cancer in a wide range of animals, from mice to chickens. In the early 1980s, Dr. Robert Gallo and his co-workers, as well as a group of Japanese researchers, showed for the first time that a retrovirus is responsible for cancer in humans. The culprit is now called human T-cell lymphotropic virus, type 1 (HTLV-1), which causes a rare and extremely aggressive adult leukemia that occurs mainly in the southern islands of Japan and parts of Central Africa and the Caribbean.