Alex P. Salam, MBChB, MSc , clinician and clinical researcher with the United Kingdom Public Health Rapid Support Team, and Peter W. Horby, MBBS, PhD, professor of emerging infectious diseases and global health at the University of Oxford, said their findings underscore the need for additional research to determine whether these viruses remain viable in semen and for how long.
“The presence of viruses in semen is probably more widespread than currently appreciated, and the absence of virus in genital secretions should not be assumed for traditionally nonsexually transmitted viruses,” they wrote in Emerging Infectious Diseases. “The investigation of virus detection and persistence in semen across a range of viruses is useful for clinical and public health reasons, in particular for viruses that lead to high mortality or morbidity rates or to epidemics.”
According to the researchers, blood-testes/deferens/epididymis barriers are “imperfect” in preventing viruses in blood from crossing into the male reproductive tract. The viruses are able to survive within testes because the immune response is restricted to enable survival of sperm.
To further investigate the persistence of viruses in semen, the researchers performed a large PubMed search limited to studies on viruses capable of causing viremia. They identified studies of 27 viruses that were detected in human semen, many of which lacked data on sexual transmission. Viruses that were found in semen included adenoviruses; transfusion-transmitted virus; Lassa fever virus; Rift Valley fever virus; Ebola virus; Marburg virus; GB virus C; hepatitis B and C viruses; Zika virus; cytomegalovirus; Epstein Barr virus; human herpes viruses 6, 7 and 8; human simplex viruses 1 and 2; varicella zoster virus; mumps virus; adeno-associated virus; BK virus; JC virus; simian virus 40; HIV; human T-cell lymphoma virus 1; simian foamy virus; and chikungunya virus.
“These 27 viruses come from diverse families, suggesting that the presence of many viruses in semen is unlikely to be exclusively dependent on specific or conserved viral epitopes, [the] ability of virus to replicate within the male reproductive tract, or common mechanisms of immune evasion,” the researchers wrote. “Other factors that may also influence whether viruses exist in semen are level of viremia, inflammatory mediators (altering blood-barrier permeability), systemic immunosuppression, male reproductive tract immune responses, presence of sexually transmitted diseases, and the virus structural stability.”
Several other viruses were detected in human testes and may also be detectable in semen, including influenza virus, lymphocytic choriomeningitis virus, phlebotomus fever virus, coxsackie B virus, echovirus, dengue virus, systemic acute respiratory syndrome virus, parvovirus, smallpox virus, vaccinia virus and rubella virus, according to the researchers.
“Given these findings, the following questions need to be addressed: which viruses are shed and remain viable in semen, for how long, and at what concentrations? The answers to these questions have implications for risks for sexual transmission and, therefore, embryonic infection, congenital disease, miscarriage, and effects on epidemiologic transmission models,” the researchers wrote.