In a paper published this April in AIDS, HAI researchers found that a significant number of people recently infected with HIV-1C, the HIV subtype predominant in southern Africa, maintain a high level of HIV (viral RNA) in their blood and semen for a much longer period than was expected. About 34% of people infected with HIV-1C maintain a high viral load for 100–300 days; 19% maintain a high viral load for 200–400 days. Viral load is the chief predictor of the risk of heterosexual transmission of HIV. The study subjects were from Botswana and South Africa.
The finding was a surprise. Earlier research done on HIV-1B, the subtype predominant in the U.S. and Western Europe, found that most recently infected individuals maintained a high viral load for several weeks, rather than many months or a year. After the initial infection, known as the acute stage, a person’s viral load drops as the body’s immune system subdues the virus and reaches what is called a viral set point. The set point can remain relatively stable for years before it climbs and a person develops full-blown AIDS.
The new finding may help explain why the AIDS epidemic is so much worse in southern Africa than elsewhere in the world. People in the early stages of HIV infection are not yet stricken with AIDS-related illnesses. If they feel healthy and don’t change their behavior, “that puts them in a very hot spot for transmission of new infections,” said HAI scientist Dr. Vladimir Novitsky, who led the study. “People with a high viral load are more likely to infect their sexual partners. If their viral load remains high for a longer period of time, they may infect more partners, increasing the number of new HIV transmissions.”
New knowledge also brings new opportunities. Most people in southern Africa with acute HIV infection and a high viral load do not qualify for antiretroviral treatment (ART) because their other health indicators, such as CD4 count, have not fallen to dangerous levels. Antiretroviral drugs are extremely effective at dropping a person’s viral load. Putting all individuals with a high viral load on ART could prevent new infections and have a profound effect on the epidemic. This is the premise behind HAI’s Mochudi Prevention Project, now underway in a village of 40,000 in southern Botswana.
“The hypothesis is that a small fraction of people with a high viral load are responsible for the majority of new transmissions in the community,” said Novitsky, who is working with HAI Chair Dr. Max Essex on the Mochudi Prevention Project. “If a person’s viral load is dropped with ART, that person stops being a potential transmitter, which would greatly benefit the community.”