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.”
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.
two-thirds (64%) of the men had recent HCV infection (under six months); the
others were chronically infected.
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
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
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,
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.”