AIDS: new viruses to fill in the blanks.

AIDS: New Viruses to Fill in the Blanks

Two new members were proposed last week for the AIDS group of viruses. One apparently causes AIDS, while the other appears harmless to humans and may even protect against AIDS. According to the researchers, the findings bring possibilities for Prevention as well as for understanding the origin of the disease.

One of the newly identified variants, named human T-lymphotropic virus type IV (HTLV-IV), was first osolated healthy prostitutes in Senegal. Max Essex of the Harvard School of Public Health in Boston, who heated the team that discovered the virus as well as a similar strain in African green monkeys, says the virus may be a "missing link" between the monkey and human viruses.

The devastating effect of the AIDS virus may be due in part to its youth: Human bodies have yet to evolve defenses against it. But the origin of the disease has been a mystery. Serum samples drawn from Africans in the mid-1970s and tested in the last few years show signs of the virus, or of a closely related one, and retrospective diagnoses of AIDS have been made for a few Africans who came to Europe for treatment at about that time.

Essex postulated last year (SN: 4/20/85, p. 245) that the AIDS virus made its way into Africans who ate or were bitten by primates infected with a closely related virus, but the idea has met with hostiliy from Africans who feel unjustly burdened with responsibility for the epidemic.

HTLV-IV is closely related to the AIDS virus: Some antibodies made in response to one virus recognize and cross-react with particles from the other, and the viruses home in on the same target in the body, a T cell subgroup of the immune system. But while the AIDS virus is lethal, people infected with HTLV-IV remain healthy. The team has followed more than 50 infected Senegalese for up to three years, and has found no signs of virus-caused illness, including AIDS. In fact, there has been only one reported case of AIDS in the entire country. "You have to wonder why [AIDS] is in neighboring countries and not there [in Senegal]," says Phyllis Kanki of the Harvard School of Public Health. And there is no evidence of asymptomatic infection with the AIDS virus in Senegal, Essex says, though "to our knowledge, HTLV-III-LAV [the AIDS virus] is present in Dakas, Senegal, where we did our study."

All this could mean, Essex suggests, that HTLV-IV affords natural protection agaisnt AIDS. At the least, the variant could serve as a natural laboratory for scientists studying the disease process in AIDS. "We fell that what we might have is a naturally attenuated variant in this general family [of human T-lymphotropic viruses]," Essex says. "It doesn't seem to be killing the same cells, although it infects them.... So we should be able to learn a lot about how people can be protected against disease development after infection with a virus of this general type."

The new findings have rekindled long-simmering competition among scientists in this area. Essex's decision to announce his findings two weeks before their scheduled publication in the April 11 SCIENCE appeared to be prompted by the release the day before of new, unpublished AIDS findings by a European team. According to Luc Montagnier of the Institut Pasteur in Paris, his team has isolated a previously inidentified AIDS-causing virus in two patients in European hospitals. Montagnier's group was the first to isolate a virus associated with AIDS which he called LAV, for lymphadenopathy-associated virus. He has named his new variant LAV-II.

While LAV-II is no cause for optimism, HTLV-IV might bring researchers closer to an AIDS vaccine. It is "totally impossible," Essex says, to use HTLV-IV itself as a vaccine, since it sets up a persistent infection of unknown outcome. But it may be helpful because it shares many antigens with the AIDS virus--most significantly, perhaps, some surface antigens that are likely candidates as the viral part that recognizes the T cell target. "i think that taking parts of this virus, to see whether or not they would be effective as a vaccine, is certainly appropriate," says Essex.

These are not likely to be the only variants found. "We predict that there will be other viruses in the spectrum that range from the African green monkey prototype ... through to the HTLV-III/LAV-type virus as we know it," says Essex. "It's quite generally understood that this family of viruses has a very sloppy means of replication and therefore a very high rate of mutation."