One of the least understood questions in virology in a recent turn of outbreaks like Ebola and Zika are that there are reports of these viruses being transmitted sexually. Now that we know that semen by itself possibly harbours a microbiome (Link) there definitely is a good chance that many different microbes can harbour in reproductive tissues such as testis. But there is no comprehensive literature on all possible viruses infecting the male reproductive tract.
A meta-analysis which searched for all the literature available on evidence of virus presence in semen turned up 3,818 PubMed search results. Screening all the literature, the authors concluded that 26 viruses can survive in human semen which can seed a viremia. A summary is shown in Table 1.
|Table 1: Viruses that are capable of causing viremia and found in human semen. Source|
It should be noted that not all viruses listed have a defined capability to be sexually transmitted. But their biological effects on variables such as sexual health is not known. It is also known what is the duration of residence and how far they can seed viremia, serve as latency and what is the likely concentration. As Alex Salam puts it, "Clinicians need to consider the possibility that traditionally non-sexually transmitted viruses can persist in semen, and this, therefore, raises the possibility of sexual transmission. Detection means that evidence of viral genetic material or viral protein was found in semen. It’s important to note that this does not mean that the virus is viable, i.e., capable of replicating. To prove this, the virus needs to be isolated and grown in cells or animals. For many of the viruses, this test has not been done, so we don’t know whether virus is viable or not."
This paper needs to be followed up with laboratory tests to establish the results. Further, this list is definitely not complete. But at least we have a more likely and possible catalogue of which viruses may be found in semen.
Salam AP, Horby PW. The breadth of viruses in human semen. Emerg Infect Dis. 2017. https://doi.org/10.3201/eid2311.171049