A dig through the literature has uncovered evidence of 27 distinct viruses from a wide variety of families capable of staying intact as they're transmitted through semen to a new host.
While not all of the microbes are confirmed sexually transmitted infections, the review does draw attention to the fact the testes seems to provide a potentially easy way for just about any kind of virus to migrate into a new home.
This latest research was inspired by the recent discovery of Zika virus RNA in the semen of infected hosts.
A pair of researchers from the University of Oxford and the Public Health Rapid Support Team in the UK embarked on a search through past papers in search of clues for any other viruses that could also be carried in seminal fluids.
To see what other nasties might be lurking alongside our sperm, the researchers ran a search through the PubMed catalogue for relevant terms, filtering out over 3,800 papers containing some mention of viruses and semen.
All up they fished out evidence of 27 viruses – including Zika – that could remain intact enough to infect the blood of a new host.
But many of the other pathogens haven't been studied as sexually transmitted infections.
It's important to note that catching virus particles isn't the same thing as an infection. There's no guarantee that viremia – the presence of viruses in your blood – will turn into a full-blown disease.
Still, it's food for thought, also raising concerns on how potentially functional viruses might affect fertility and embryonic development.
The real surprise was the diversity of viruses represented in this catch.
Since the agents came from all manner of backgrounds, there was no clear sign of a single tactic they might have all used to jump from the host's blood into their seminal fluids.
The testes aren't just any organ in the body. To prevent the body from declaring war on sperm and the germ cells they come from, a tight wall of cells called the Sertoli cell barrier blocks most immune responses, making the tissues a kind of immunological VIP zone.
That's not only good news for the sperm, it's potentially good news for virus particles.
They might not get much opportunity to replicate in testicular tissues, but beyond the reach of the immune system they would still have a hassle-free ticket to greener pastures.
With such a diversity of virus families jumping on that human Hyperloop, the researchers have speculated there could be a plethora more yet to make an appearance in the literature.
Viruses responsible for diseases such as influenza, SARS, and dengue have been found in the testes, making it a fair question to ask if they're one small step away from an easy passage.
"Which viruses are shed and remain viable in semen, for how long, and at what concentrations?" ask researchers Peter Horby and Alex Salam in their paper.
There is also the question of whether any of these stowaways could potentially bunk down and wait out any chemical assaults in the relative safety of the testes, making treatments less efficient.
The review certainly raises more questions than provides answers.
But with Zika taking a number of people by surprise, we should be thinking outside of the box when it comes to the spread of viruses.
This research was published in Emerging Infectious Diseases.