New York Times Outlines the ‘AIDS Questions that Linger’
As scientists, doctors and health officials prepare for next week's Conference on Human Retroviruses in Chicago, New York Times science writer Dr. Lawrence Altman has compiled an assortment of answers from leading HIV/AIDS experts to questions that still "linger" about research, vaccines, treatment and prevention. UNAIDS Executive Director Dr. Peter Piot and Dr. Stefano Vella, president of the International AIDS Society, said that "reviewing unanswered questions could prove useful as a measure of progress for AIDS and other diseases." The questions, and the experts' responses, appear below.
- How many people are infected in the United States and has the rate changed in recent years?
Since only 36 states report statistics on HIV infections, the "precise" number of HIV-infected individuals is unknown. The CDC estimates that over the last decade, the number of newly infected people in the United States has "remained stable" at 40,000 per year. Gay men accounted for about 40% of all infections in 1999.
- Why does AIDS predispose infected persons to certain types of cancer and infections and not others?
Altman explains that while individuals with AIDS are "much more prone to certain cancers like non-Hodgkins lymphomas and Kaposi's sarcoma," they are not at increased risk for breast, colon and lung cancers. "This pattern suggests that an impaired immune system [found in individuals with AIDS] does not allow common cancers to develop," Altman writes. He adds that an "[e]qually puzzling" trend is the development of infections such as pneumonia and meningitis in people with AIDS. Dr. Henry Masur, an official at the National Institutes of Health, added, "we do not know very much more about why [certain cancers and diseases develop in AIDS patients] than we did 20 years ago when the first work was done."
- What route does HIV take after it enters the body to destroy the immune system?
When transmitted sexually, HIV must "cross a tissue barrier" to enter the body and eventually travels through lymph vessels to lymph nodes and throughout the lymph system, Altman explains. How HIV crosses the tissue barrier "is still unclear," Michel Kazatchkine, the director of the French national agency for AIDS research in Paris, said. But information concerning HIV's entry into the body is "key" to developing products designed to block transmission, such as microbicides, Altman says.
- How does HIV subvert the immune system?
Although HIV kills immune system cells, which leads to a weakened immune status, the rate at which this occurs varies widely among HIV-positive individuals. Scientists have wondered whether elements of the immune system are responsible for the "widespread" variation in disease development, and if so, can the elements be identified and used to "stop progression to AIDS" and "possibly prevent infection in the first place." Dr. William Schaffner, head of preventive medicine at Vanderbilt University's medical school, said that the information could be the "key" to developing an effective vaccine.
- What is the precise function of HIV's genes?
Altman writes that the functions of HIV's nine genes remain only "partly known," but that a "complete blueprint" could provide information for the development of new treatments and vaccines. One HIV gene was labeled "nef" -- negative factor -- because it was thought to inhibit HIV, but researchers discovered that it actually accelerates the virus' ability to infect its host. Researchers' hopes of developing a vaccine derived from virus with a deleted nef gene were "shattered" in 1999 when a man infected with a nef-deleted strain of HIV developed AIDS.
- What is the most effective antiHIV therapy?
"In theory, early treatment should offer the best chance of preserving immune function," Altman writes. However, new NIH recommendations soon to be released advise delaying treatment until a patient's CD4+ T cell count is fairly advanced. "The change in recommendation reflects the fact that many patients and doctors already choose to postpone treatment because of fears that they will have no other drugs to use when resistance and other problems develop later on," Altman adds. He notes one potentially successful treatment strategy -- intermittent therapy -- which involves periods of antiretroviral therapy interspersed with intervals without drug treatment. Questions concerning whether this type of treatment will work and how to best deliver antiretroviral therapy to developing nations with "scarce" medical facilities remain "unanswered."
- Is a vaccine possible?
While there is "little question" that an effective vaccine is "crucial to controlling the epidemic," there is "considerable dispute" over the level of protection offered by inoculation. However, Altman points out, most vaccines protect about 90% of recipients.
- In the absence of a vaccine, how can HIV be stopped?
Research in Africa has shown a link between the amount of HIV in the bloodstream and the risk of transmission, but studies attempting to examine how this link relates to an individual's ability to transmit the virus have been "rare." However, the spread of HIV can be slowed by abstinence, HIV testing and counseling and prevention programs that stress condom use, Altman writes. But more "focused behavioral research" is needed to examine how to best communicate prevention methods to young people and different ethnic groups, Altman adds.
- Why do most babies born to infected mothers escape infection?
"Relatively little research" has been conducted on why 75% of infants born to HIV-infected women "escape" the virus, Dr. Jose Esparza of UNAIDS, said.
- Why do HIV rates differ so greatly among regions in Africa and elsewhere?
Dr. Harold Jaffe, an AIDS researcher at the CDC, said that several theories concerning the regional disparity in infection rates exist. He said that one theory involves variations in patterns of sexual activity, including the number of sexual partners, age at first sexual intercourse and frequency of sexual encounters with prostitutes. Another theory relates to the frequency of other STDs, specifically those that break the skin, thus facilitating HIV entry. A third theory involves other "coexistent infections," such as malaria or tuberculosis, that can "increase the amount of HIV in the blood," Altman writes. Another theory states that uncircumcised males "appear to be more susceptible to HIV than circumcised men." Piot added that while a plethora of theories exist, "there is no simple explanation" for the regional differences.
- Where did AIDS come from?
"We can only guess," Altman answers.