Most HIV cases traced to transmission of single virus

May 22 2008

Most HIV cases can be traced to the transmission of a single virus, according to a study published online Monday in the Proceedings of the National Academies of Science, the Birmingham News reports. According to researcher George Shaw, a professor at the University of Alabama-Birmingham, the findings are surprising and could have an impact on HIV/AIDS vaccine development.

For the study, Shaw and colleagues analyzed blood samples from 102 people who had recently contracted HIV. The study was funded by NIH's National Institute of Allergy and Infectious Diseases and the Bill & Melinda Gates Foundation. The researchers genetically analyzed the samples and were able to count generations of HIV. They found that 76% of the cases could be traced back to a single virus. The remaining 24% could be traced to two to five viruses, according to Shaw. Shaw noted that in the "vast majority" of cases, a single virus has "gone across the sexual mucosa, and that virus has infected a cell." He added, "That cell then makes a lot of virus. Now you just have a firestorm of HIV replication in the next couple weeks. Very quickly the person is populated by millions of viruses." According to Shaw, the findings help explain why it usually takes several exposures for a person to contract HIV, why transmission of the virus is so inefficient and why condoms help prevent HIV transmission.

The findings are significant because they indicate that if researchers are "trying to develop a vaccine or microbicide or whatever to prevent [HIV] infection, the only thing it has to do is prevent the transmission of a single virus," Shaw said. He added, "That should be possible. All you have to do is provide some additional block to what already is an efficient process." The findings "provide light on what was previously a very cloudy area of HIV infection," Shaw said, adding, "It puts acute and early transmission of HIV-1 in very sharp focus."

Most other sexually transmitted infections -- such as gonorrhea and syphilis -- "invade the body en masse," according to the News. "They just all come across 10, 20, 100, 200 bacteria or spirochetes," Shaw said. Several research centers worldwide were involved in the project, including Duke University, the University of California-San Francisco, the University of Cape Town in South Africa, the University of Massachusetts-Amherst, the University of North Carolina-Chapel Hill, the University of Maryland, the University of Rochester, and the Los Alamos National Laboratory and the Santa Fe Institute in New Mexico (Parks, Birmingham News, 5/20).

The study is available online (.pdf).