Researchers from the University of Missouri discovered that rats caught in various locations near city sewers during three months of 2021 are susceptible to infection by multiple strains of SARS-CoV-2, the virus that causes Covid-19.
According to the findings of their study, which were published on Thursday in the journal mBio, 13 of the 79 rats (16.5%) tested positive for the virus, a figure that can be extrapolated to potentially 1.3 million of the city’s eight million rats.
The researchers discovered that not only could the rats be infected with the virus’s Alpha, Delta, and Omicron variants in both their upper and lower respiratory tracts, but that SARS-CoV-2 mutated after infection to adapt to its new hosts – something previously unknown.
The findings “highlight the need for further monitoring of SARS-CoV-2 in rat populations for potential secondary zoonotic transmission to humans,” according to the study’s principal investigator, Henry Wan, in a press release accompanying the study’s publication.
Initially, the Covid-19 pandemic was blamed on zoonotic transmission of a mutant bat coronavirus to humans via an intermediate host in a wet market in Wuhan, China. However, subsequent evidence indicated that the virus was spreading in other parts of China as early as October 2019, before the first Wuhan cases were discovered — and researchers believe some cases occurred in Europe and the United States in the final months of 2019.
According to a recent investigation by the US Department of Energy, the virus was most likely “leaked” from a Chinese lab. Beijing has responded that the World Health Organization’s own investigation concluded that the Wuhan lab was “extremely unlikely” to be the source of the outbreak.
Rats are not the only ones who are vulnerable to the virus that causes Covid-19. In Denmark, 17 million mink were preemptively exterminated in 2020 after some were found to be infected with a new strain of the virus thought to be dangerous to humans, a decision that was later ruled illegal.
Last year, Hong Kong ordered the culling of 2,000 imported hamsters after a resident contracted Covid-19 from handling them in a pet shop; a ban on owning foreign hamsters was also imposed.
