In early 2010, scientists at the University of California San Diego’s Center for AIDS Research (CFAR) discovered that seminal HIV infection among men who have sex with men is transmitted through the HIV cell’s RNA, and not the DNA as was previously thought. Later that year it was determined that this is also the case for women who are infected through sex with men – that is, through HIV cells in semen transmitting their RNA structure to the newly infected individual. Understanding this connection is critical, because, “If we want to stop the HIV epidemic, then we must know the mechanisms by which HIV uses human sex to spread,” according to the principal researcher, Davey Smith, MD, MAS. Smith is an associate professor of medicine at the University of California’s San Diego’s Division of Infectious Diseases, and is director of the CFAR’s Viral Pathogenesis Core.

The scientists made this initial discovery of the virus’s transmission by studying male partners in which one man had recently infected the other man. They compared the genetic characteristics of the HIV cells in both partners, knowing that the virus mutates at an extraordinary rate. They learned that there was more of a shared commonality between the viruses found in the seminal plasma – the semen and fluids surrounding them – than the viruses that were located in the seminal cells. HIV’s DNA is commonly found in the host’s cells, where RNA is mostly stored in the host’s plasma. With this asymmetrical commonality between the virus found in the plasma versus the virus inside the host’s cells, the scientists were able to locate the culprit of the initial transmission, which is the virus’s RNA; with this asymmetrical commonality found in every partnership of the men they studied, they determined that it is not a mix of HIV RNA and DNA infecting an individual, but that the RNA, alone, was the transmitter.

Now knowing this source of HIV transmission, scientists and researchers have been able to develop several weapons against HIV infection over the past five years. The HIV cells in semen are now understood more, and with this understanding researchers have been able to determine and develop several things. One discovery is that if a person has no detectable amount of HIV in their bloodstream, as they have been recently infected or because they are taking a successful regimen of antiretroviral medications, there can still be a contagious amount of HIV cells in their semen – and though the possibility of infection is low at that point, it is still possible. Researchers have also been able to develop vaginal gels and ointments – called vaginal microbicides – which are able to attack the HIV cell’s RNA before transmission can take place by infected semen, along with further developing antiretroviral medications which target the virus’s RNA and make it impotent towards further transmission. Though this discovery has not led to a cure within the past five years, it has certainly brought us closer to that possible cure, and has helped prevent further transmission of HIV for thousands.