Researchers from the University of California in San Diego have discovered which genetic form of HIV is transmitted between men who have sex with men, HealthDay News reports. Their findings are published in the February 10 issue of Science Translational Medicine.

“By knowing the origin of the transmitted virus, scientists may be able to develop new vaccines, vaginal microbicides and drugs to prevent the spread of sexually transmitted HIV,” study author Davey Smith, MD, an associate professor of medicine at the University of California San Diego, said in a statement.

Authors studied HIV in semen, which is comprised of seminal cells and a fluid called seminal plasma. Particles of the virus containing RNA exist in the fluid, while the seminal cells hold HIV DNA.

“Until now, it had not been established whether HIV RNA or DNA is transmitted during sex,” Smith said. “By analyzing the genetic differences between these two forms and the virus that was ultimately transmitted to newly infected individuals, we found that it was the HIV RNA form present in seminal plasma that was transmitted.”

With regard to male-to-female HIV transmission, Smith explained, “Since the vast majority of women are infected with HIV by exposure to the virus in semen, HIV RNA in the seminal plasma is the likely culprit, but this needs to be confirmed.”