Hepatitis C virus (HCV) is present in the semen of a third of co-infected HIV-positive men who have sex with men (MSM), investigators from the United States report in Open Forum Infectious Diseases. Levels of HCV in semen were plausibly high enough to transmit the infection. The authors believe their findings show that condoms should be used for anal sex to prevent HCV transmission.
“Based on the findings of our study, an average ejaculate would deliver between 50 and 6,630 IU of virus into the rectum of the receptive partner,” write the investigators. “These seemingly low HCV levels could play a significant role in sexual transmission of HCV when deposited into a rectum whose surface epithelial layer has been disrupted through anal intercourse.”
The investigators note that HCV transmission can occur through the parenteral route – injections, medical equipment or blood transfusions – by the transfer of only 10-20 hepatitis C virions (somewhere between 10 and 100 IU/ml depending on the assay used), suggesting that when virus is being shed, HCV transmission is possible if semen is ejaculated into the rectum.
There is a well-documented epidemic of sexually transmitted HCV among HIV-positive MSM. However, there is no consensus about the sexual risk factors for infection with HCV. Receptive unprotected anal intercourse, especially with ejaculation, has been identified as a risk factor in some research, but other studies have shown that sexual practices, such as fisting, that cause trauma to the rectum are the main risk factor.
A team of US investigators hypothesised that HCV would be detected in the semen of MSM with HIV and HCV co-infection, and that semen is the vector of infection. They therefore designed a study involving 33 co-infected men who provided paired blood and semen samples. HCV viral load was measured in both blood and semen.
Approximately two-thirds (64%) of the men had recent HCV infection (under six months); the others were chronically infected.
Participants provided 59 semen samples that could be evaluated for the presence of HCV.
Shedding of HCV in semen was detected in eleven (33%) men and a total of 16 (27%) semen samples.
Comparison of men with and without HCV in their semen showed that HCV viral load in blood was significantly higher in men shedding virus in their semen (p = 0.002).
Median HCV viral load in semen specimens with detectable virus was 1.49 log10 IU/ml. The median difference between HCV levels in blood and semen was 5.08 log10.
There was a significant correlation between HCV viral load in blood and semen overall (p = 0.001) and in the sub-group of patients with recent infection (p = 0.02), but not in the sub-group of patients with chronic infection. Although HCV shedding in semen tended to be associated with a higher HCV viral load, shedding did occur in people with lower viral load, and it varied between sampling occasions (two to four weeks apart), indicating that shedding is not consistent. The researchers did not report whether or not sexually transmitted infections or herpes viruses influenced shedding.
Comparison of the recent and chronic sub-groups showed there were no significant differences in the proportion shedding virus in their semen (21% vs. 38%, respectively), or in median semen HCV viral load (1.32 log10 and 1.77 log10, respectively).
But if HCV is shed in semen in potentially infectious quantities, why is sexual transmission of HCV extremely rare in heterosexuals?
“The rectal mucosa changes generated by anal intercourse alone, without more significant trauma, may allow absorption of HCV from semen,” conclude the researchers. “Our data therefore strongly support that condoms should be used during anal intercourse among MSM to prevent HCV acquisition, regardless of serostatus.”
Turner SS et al. Shedding hepatitis C virus in semen of HIV-infected men. Open Forum Infectious Diseases, online edition, 2016.