Important note: Information in this article was accurate in 1999. The state of the art may have changed since the publication date.
Newsday - February 4, 1999
Laurie Garrett - Staff Correspondent
"The virus can evolve resistance to members of each class of drugs," Dr. John Mellors of the University of Pittsburgh said in a news conference yesterday. "And given enough time it can develop cross-resistance to all members of each class . . . and transmission of cross-resistant viruses from person to person is a serious problem."
Mellors said recent studies indicate that about 3 percent of all new infections in the United States involve viruses that are resistant to the family of drugs that includes AZT and ddI. Five to 10 percent are resistant to the family that includes nevirapine, while as many as 10 percent are resistant to the protease inhibitor class of drugs.
"I don't think resistance is inevitable" in every patient, Mellors added. "But that's not to say that reduction of viral loads to below the limits of detection signifies complete cessation of viral replication."
Some very simple mutations - including single changes in an HIV gene - can increase the virus' ability to resist a class of drugs by more than 10,000-fold, reported Dr. Brendan Lardner of the Virco Company in Cambridge, England. "There really are a lot of these kinds of mutations around," he said.
Meanwhile, Dr. Luc Perrin of the University of Geneva, said he found one mutation against AZT that has increased steadily in prevalence. In 1988, less than 4 percent of HIV cases found in Europe, the United States and Australia carried the mutation, he said, and now 13 percent do.
More alarming has been the rising prevalence of viruses resistant to protease inhibitors, a class of drugs that have been in widespread use for only about 2 1/2 years. No resistant strains were seen in 1997 in Europe, Perrin said. But by the end of last year, anywhere from 3 to 9 percent of European HIV strains were found to be resistant.
In a separate study, Dr. Robert Colgrove of Harvard Medical School analyzed viruses carried by 75 newborn, infected babies and found that more than half carried AZT resistance.
Even more troubling are discoveries of different types of drug resistant viruses carried in various parts of a single individual's body. A University of California in San Francisco study, for instance, showed that some patients had multidrug-resistant HIV in their brains, but not in their blood. This means that simple blood tests failed to see that drug therapy wasn't working, and the patients died as HIV decimated their central nervous systems.
Bette Korber of the Los Alamos National Laboratory and Dr. Steven Wolinsky of Northwest University have analyzed genetic details of thousands of viruses, collected from around the world over nearly 30 years. They've found that the virus' genome changes "at a rate of 1 percent per year, in terms of its evolution," Wolinsky said.
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