Your feline friend may be bringing home more than you bargained for. Those mousey hunting trophies dropped at your door might contain exotic viruses completely unknown to us, as new research suggests.
In a recent paper, researchers in Florida describe discovering a microbe inside a dead rodent that had been caught by one of the scientists’ pets, a black male cat named Pepper. Thankfully, this unexpected discovery didn’t make Pepper sick, but the virus might still pose a risk to humans.
There are all sorts of viruses and other microbes left uncatalogued in the world. And while most of these pose no danger to us, some may have the machinery and opportunity needed to jump across species and become a real problem—also known as a spillover event. This latest discovery, made by researchers at the University of Florida, illustrates the value of looking for viral threats in less conventional places.
Pepper belongs to John Lednicky, a UF microbiologist and long-time virus hunter who lives in Gainesville, Florida. In early May 2021, Pepper dragged in a fresh rodent kill, a common cotton mouse (Peromyscus gossypinus). While Pepper’s penchant for dropping off furry gifts was nothing new, Lednicky decided to do something different with it this time. He wondered if these mice could possibly carry mule deerpox virus (MDPV), a potentially emerging pathogen in white tailed deer that he and others had recently found in the state. So, he and his team brought the dead rodent back to the lab to study it further.
Their tests detected a viable virus from Pepper’s specimen (meaning a virus that could grow inside certain host cells in the lab), but it didn’t appear to be the mule deerpox virus. More advanced testing eventually revealed that they had instead found something previously never seen in the U.S.: a type of jeilongvirus.
Jeilongviruses are part of a broad viral family called paramyxoviruses, some of which include germs that make us sick, like those that cause measles and mumps. Other jeilongviruses have been found in Africa, Asia, Europe, and South America. They seem to primarily infect rodents, but some are capable of also infecting other species like bats and cats. And the team’s early research suggests that their virus is unlike any other of its kind seen to date. In the lab, they found that it could infect and grow inside certain human and other primate cells just as easily as it could inside rodent cells—a worrying sign that it has spillover potential.
The researchers have dubbed their novel microbe the Gainesville rodent jeilong virus 1 (GRJV1). They detailed their findings on GRJV1 in a paper published last month in the journal Pathogens.
“Millions of viruses are predicted to exist that have not yet been isolated. This one is of great interest because it appears to be a ‘generalist’, able to affect cells from different types of animals including humans,” Lednicky told Gizmodo.
The actual threat that GRJV1 may pose to us right now is probably low. Even if it could infect people outside the lab, we generally aren’t coming into close contact with potential rodent vectors all that often these days. The researchers note that even well-known, deadly rodent-borne germs like hantaviruses only occasionally cause outbreaks in humans.
At the same time, many paramyxoviruses that sicken humans are respiratory infections, meaning they cause the sort of symptoms we would call a cold. Even when we do see a doctor for these symptoms, they usually only test for the most common culprits, like influenza or RSV. So it’s certainly possible that GRJV1 has been making people sick for a while but going unnoticed.
The scientists say that more research is needed to understand how GRJV1 interacts with its rodent hosts and other potential animals—does it make them sick, for instance? And it’s still important to figure out whether GRJV1 can or has already spilled over to humans in the past. While most spillover events are isolated and lead nowhere, the occasional pathogen can sometimes successfully jump over the species barrier and become a newly established human disease. The virus formerly known as monkeypox is one such recent example.
Lednicky does hope to explore GRJV1 more in the future, starting with animal studies and then aiming to see if any human populations are carrying antibodies to it (antibodies being a sign of past infection). But unfortunately, the resources required to study these possible threats are often in short supply.
“The problem we encounter is lack of funding. For example, the NIH no longer funds many ‘surveillance’ studies. And when a new pathogen is found, funding agencies tend to fund work only for those which have caused outbreaks in humans. For researchers like me, the best option would be to receive unrestricted private funding, or of course, dedicated funding from the state or from the federal government,” he said. “The work we do is very expensive, requires extensive training and safety procedures, and specialized secure facilities.”
For his part, Pepper’s virus expedition left him no worse for wear, and he’s just as much of a rodent catcher today as he’s ever been. That said, he might be even more of a cautious scientist than anyone’s giving him credit for.
“Cats have evolved to eat rodents, so they are probably not affected by most of the pathogens they carry,” Lednicky said. “Interestingly, Pepper will typically eat the front half only of a rodent. In general, he leaves the kidneys, spleen, and intestines uneaten. Does he do this out of instinct? I don’t know. But many of the dangerous rodent-borne viruses are precisely found in the latter organs.”
This article has been updated with quotes from one of the study’s authors.
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