PITTSBURGH, Penn., June 25--Current testing practices, which typically measure the viral load or the amount of freely circulating genetic material of HIV-1 in the blood, may not accurately detect the amount of virus in semen, say researchers from the University of Pittsburgh Graduate School of Public Health (GSPH).
In a report presented on June 30 at the 12th World AIDS Conference, Pitt researcher, Phalguni Gupta, Ph.D., emphasized that testing viral load levels in semen as well as targeting treatments to sites of seminal virus production may offer physicians a better way to monitor viral activity in HIV-infected patients and also stem transmission of HIV-1.
"To accurately assess how easily and how much HIV can be transmitted during risky sexual contact with HIV-infected individuals, we can't rely on blood tests. Instead, we need to test viral load levels in semen," said Dr. Gupta, who is a professor of infectious diseases and microbiology at Pitt's GSPH.
"Most of the HIV-infected men in our study had very high levels of virus present in their semen at certain time points and then at other times had a lower amount. This indicates that some men may be more likely to transmit the virus during risky sexual behaviors at certain times."
Dr. Gupta and his colleagues are the first to report HIV in semen can fluctuate greatly in some HIV-infected men and does not correspond to viral levels in blood. A previous study by the Pitt group found differences between the types of HIV found in the blood and semen of some HIV-infected men.
"These results, taken together with our new findings, indicate that virus found in the semen originates from a separate site, different from that of virus that circulates throughout the body." remarked Dr. Gupta. "If we locate the site where seminal virus is produced, we may be able to target treatments to this site and suppress replication of viral strains which may be different than the ones found circulating throughout the body. This is absolutely crucial to stemming transmission of the virus."
Previous research has provided evidence that circulating virus in the body is produced in the blood, whereas, Dr. Gupta thinks seminal virus may originate in the prostate. He and his colleagues are conducting further research to understand more about replication of seminal virus as well as viral transmission through sexual contact.
The Pitt researchers measured the amount of genetic material of the virus, HIV-1 RNA, in the semen and blood of 18 men infected with HIV-1. The amount of virus detected in the blood samples from all of the study participants remained at the same level throughout the study, while viral levels in semen fluctuated from very high levels to low levels in 44 percent of the study participants.
"This intermittent 'shedding' of HIV-1 in this group of men occurred even though no changes were detected in the viral load from the blood samples," said Dr. Gupta. The researchers also measured the number of total CD4 T cells, activated CD4 T cells and a certain growth hormone in semen to see if these factors were controlling replication of seminal virus.
CD4 T cells, the initiators of immune responses against HIV-1 and other foreign substances in the body, are the primary targets of HIV-1. A change in the number or activity of these cells would explain the discrepancy in viral levels between the blood and semen in HIV-infected men. However, researchers found no unusual measurements of these factors and concluded that they did not cause the changes in seminal viral load.
Dr. Gupta and his colleagues are currently conducting studies to determine why the levels of virus in semen fluctuate in some HIV-infected men.
He found that in 28 percent of the participants in this study, HIV-1 was not detected in semen samples. However, in another 28 percent of the men, HIV-1 was produced at consistent levels throughout the 10 weeks of the study.
"Again, this finding points to the necessity of viral load testing of semen samples in addition to testing blood samples. Seminal viral load varies not only from one individual to the next, but also in some HIV-infected men, the levels of virus in semen can vary from one day to the next," said Dr. Gupta.
"The good news is that a previous study by our group has demonstrated treating HIV-infected men with a combination of three potent drugs can reduce viral levels in both semen and blood," he added. But for some patients who are not undergoing therapy, they may be "shedding" HIV-1 at higher levels, which increases the likelihood of infecting others with the virus through risky sexual contact.