Brown rat

(© John Sandoy -

PRINCETON, N.J. — Rats are already major public health and hygiene problem many big cities worldwide. Now, a new study warns that waves of rodents could become the carriers of another deadly health crisis — another COVID-style pandemic.

Rodents are notorious for carrying and spreading diseases throughout history, including the bubonic plague. Researchers from Princeton University say rats can also be symptomless (or asymptomatic) carriers of coronaviruses too.

Their study finds these animals have developed a resistance to pathogens from repeated ancestral infections. Lead author Professor Mona Singh says this increases the likelihood that modern rodents could carry COVID-like viruses and infection the population.

Animal-to-human transmission is an ongoing problem

coronavirus rodent
Binding of a SARS-CoV-2 spike protein (red) to an ACE2 receptor (blue) leads to the penetration of the virus into the cell, as depicted in the background. (CREDIT: Juan Gaertner,, CC-BY 4.0)

Scientists believe SARS-CoV-2, the virus that causes COVID, may have a zoonotic origin — meaning it jumped from an animal to humans. Studies have pointed to bats in China passing COVID-19 on to another species – possibly pangolins – before reaching humans. Bats also harbor numerous SARS-like viruses without getting ill.

Researchers say identifying other creatures that have adapted tolerance mechanisms to coronaviruses is important. They are potential “viral reservoirs” that can spread new pathogens to people, leading out widespread outbreaks.

Globalization, urbanization, climate change, increased human-animal contact, and health worker shortages all help to spread viruses to other continents, creating a situation like 2020’s pandemic. Study authors that there have been three pandemics since 2000, SARS (severe acute respiratory syndrome) in 2003, swine flu (H1N1) in 2009, and now COVID-19.

SARS reportedly spread from cats and bats in China and swine flu originated in an intensive pig farm in Mexico. In between, there have been regional outbreaks of bird flu from poultry and MERS (Middle East respiratory syndrome) from camels.

There has also been cases of Ebola virus outbreaks originating in monkeys and pigs, Rift Valley fever coming from livestock, and West Nile fever and Zika virus coming from mosquitos and other animals.

Rats are prime candidates to carry SARS

Prof. Singh and graduate student Sean King performed an evolutionary analysis of the protein spikes on SARS viruses, which infect hosts and hijack cells. They attach themselves to the ACE2 receptors, slicing into the cell to replicate more of the virus.

The study shows primates had highly conserved sequences of amino acids in the sites that bind SARS viruses. Rats and mice had a greater diversity and an accelerated rate of evolution in these spots. Overall, the results showed SARS-like infections have not been evolutionary drivers in primate history.

However, some rodent species have been exposed to these illnesses repeatedly over a considerable evolutionary period.

“Our study suggests that ancestral rodents may have had repeated infections with SARS-like coronaviruses and have acquired some form of tolerance or resistance to SARS-like coronaviruses as a result of these infections,” Prof. Singh says in a media release.

“This raises the tantalizing possibility that some modern rodent species may be asymptomatic carriers of SARS-like coronaviruses, including those that may not have been discovered yet.”

Earlier this year, a study published by the United Kingdom’s top scientific advisers, SAGE, found coronaviruses could be transmitted by rats. Studies also show that rats can catch COVID-19 from people, particularly more recent strains which are more transmissible.

The study appears in the journal PLOS Computational Biology

South West News Service writer Mark Waghorn contributed to this report.

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