Rats, whose urban populations skyrocketed during the pandemic, have now joined the list of wild animals thought to be capable of infecting and transmitting the virus that causes COVID-19, according to a new study.
IN Study published Thursday in the journal mBio, researchers showed that rats are like dogs, cats, hamsters, ferrets and other close companions of the person — can pick up a pandemic virus from their environment.
They don’t seem to get very sick; none of the wild rats deliberately infected in the lab lost weight or died as a result. But when rats were exposed to alpha, delta, and micron variants of the SARS-CoV-2 coronavirus, the researchers found evidence for reliable virus replication in the animals’ nose, mouth, throat, and lungs.
In addition, a detailed examination of 79 so-called brown rats (Rattus norvegicus) collected in and around the New York sewers found clear signs that 13 of them had been exposed to the coronavirus and developed an immune response. Indeed, PCR testing of rat respiratory tissue showed that four out of 79 rats had active infections when they were euthanized.
The study was conducted by scientists from the US Department of Agriculture, the Walter Reed Army Research Institute and the University of Missouri. This brings to 11 the number of known wildlife “reservoirs” for the pandemic virus, which has also been shown to infect deer, mink, otters, gorillas, lions and tigers.
The presence of the virus in all of these species not only ensures that the coronavirus never disappears from our environment. It also raises the possibility that as the ever-changing virus adapts to new and completely different hosts, it will evolve in ways that make it unrecognizable to people who thought they were immune to it.
Brown rats, also known as Norway rats, have coexisted with humans for millennia and are numerous vectors of human disease. Exposure to their faeces, urine or saliva has been known to spread hantavirus, leptospirosis, lymphocytic choriomeningitis, tularemia, and salmonella.
As the pandemic subsides, new findings suggest a frightening scenario in which feral rats, whose populations in US cities have skyrocketed over the past three years, could become not only a vector for human re-infection, but also a source of new variants. that eludes our defenses against vaccines or past infections.
If the coronavirus recombines with another rat-borne virus, or if it simply evolves to spread more easily in this population, the result could be a new pathogen that could reset the pandemic, the study authors said.
The findings highlight the “need for further monitoring of SARS-CoV-2 in rat populations for potential … transmission to humans,” they wrote.
Other researchers suggested that biological differences between humans and wild rats made this population of wild animals particularly fertile ground for introducing mutations in the SARS-CoV-2 virus.
The authors cite research that suggests that rodents may have played a role in the evolution of the Omicron variant. This assumption is based on the fact that some of the Omicron mutations improved the ability of the virus to attach to rodent cells even more than they improved its attachment to human cells. But co-author Henry Wang of the University of Missouri School of Medicine acknowledged that “this is still just speculation.”
The problem remains to know whether and how infected rats can transmit the coronavirus to humans.
The authors of the study demonstrated that under laboratory conditions, rats infected with a related coronavirus developed infections and shed the virus. And just like humans, these rats can get re-infected.
The discovery that these infected rats are able to shed their germs leads to the discouraging prospect that when free-range rats scurry over surfaces people touch, their noses can deposit respiratory secretions that deliver the virus to humans. Bye aerosol transmission has been the main means of human spread of the coronavirus, transmission of the virus through touch is also a concern.