Study finds rat carrying multiple variants of Covid virus in US

A new study has demonstrated that rats are susceptible to infection with Alpha, Delta and Omicron variants of SARS-CoV-2.

In the study, published in the journal mBio, the researchers set out to determine whether the SARS-CoV-2 virus in humans has been transmitted to the rat population in urban areas of the US, specifically New York City, and if so, which SARS-CoV-2 variant caused those infections.

Biologists collected and processed samples from 79 rats for virological studies and genomic sequencing.

They found that the rats were exposed to SARS-CoV-2 and showed a possible link to the viruses that were circulating in humans during the early stages of the Covid-19 pandemic.

Specifically, 13 of 79 rats (16.5 per cent) tested positive.

"Our findings highlight the need for further monitoring of SARS-CoV-2 in rat populations for potential secondary zoonotic transmission to humans," said principal investigator Henry Wan, Professor and Director of the Center for Influenza and Emerging Infectious Diseases at the University of Missouri.

"Overall, our work in this space shows that animals can play a role in pandemics that impact humans, and it's important that we continue to increase our understanding so we can protect both human and animal health," he added.

Two previous studies suggested that rats in Asia (Hong Kong) and Europe (Belgium) were exposed to SARS-CoV-2; however, it is unknown which SARS-CoV-2 variant these rats were exposed to in both studies.

Further, in the new study, the researchers set out to investigate rat susceptibility to SARS-CoV-2 variants.

They conducted a virus challenge study and showed that Alpha, Delta and Omicron variants (variants found in humans) can cause infections in rats (wild-type Sprague Dawley rats), including high replication levels in the upper and lower respiratory tracts and induction of both innate and adaptive immune responses.

Susceptibility to infection varied by type of variant, they noted.

"Our findings highlight the need for further monitoring of SARS-CoV-2 in rat populations to determine if the virus is circulating in the animals and evolving into new strains that could pose a risk to humans," Wan said.

"SARS-CoV-2 virus presents a typical one-health challenge which requires collaborative, multisectoral and transdisciplinary approaches to fully understand such challenges," he added.