They are hopeful that findings of the study will have important implications in developing prevention strategies including vaccination for HIV.
"If we want to stop the HIV epidemic, then we must know the mechanisms by which HIV uses human sex to spread," said principal investigator Davey Smith, MD, MAS, associate professor of medicine at the University of California San Diego.
Using a genetic analysis called phylogenetic analysis, the researchers examined a group of gay and bisexual men who had transmitted the HIV virus to other men.
In order to identify the rapidly mutating HIV viruses, the scientists analyzed the blood and the semen samples of the transmitting partners.
Most of the sexually transmitted HIV infections result from exposure to the HIV virus in semen—the organic fluid containing sperms, the male reproductive cells.
The researchers explained that the semen is made up of seminal cells and a fluid around these calls called seminal plasma.
The seminal plasma contains the HIV particles with Ribonucleic acid (RNA), while the HIV DNA exists in the infected seminal cells.
RNA is a vital molecule that helps to control which genes are active as well as how active they are.
Outcome of the study
On analyzing these genetic differences in HIV men, and their infected partners, the researchers found that the virus is transmitted via the seminal plasma, and not the seminal cells among bisexual partners.
"Until now, it had not been established whether HIV RNA or DNA is transmitted during sex," Dr. 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.”
As the study was carried out among malen couples, the findings did not confirm the transmission of HIV via seminal plasma in women.
The results need to be replicated in larger trials, therefore, the findings should not be extrapolated, cautioned the researchers.
The study appears in the Feb. 10 issue of the Journal Science Translational Medicine.