Ferrets, cats most susceptible to COVID-19 infection after humans, study finds

TORONTO -- Ferrets and cats are among the animals that are most susceptible to coronavirus infection after humans, according to a new study.

The study, carried out by researchers at the Centre for Genomic Regulation (CRG) in Barcelona, found that civets and dogs are also among the animals with a high susceptibility to SARS-CoV-2, the virus that causes COVID-19.

According to the findings published in the peer-reviewed journal PLOS Computational Biology, ducks, rats, mice, pigs and chickens had lower or no susceptibility to infection compared to humans.

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CRG director and senior author of the study Luis Serrano said the findings offer clues why minks -- which are closely related to ferrets -- are being infected by the coronavirus.

"Knowing which animals are susceptible to SARS-CoV-2 helps us prevent building up animal reservoirs from which the coronavirus can re-emerge at a later date," Serrano said in a press release.

Serrano added that the mink infections seen across Denmark and in parts of Canada have likely been made worse by the animals’ packed living conditions and close contact with human workers.

The researchers analyzed 10 different species in the study. The first five - humans, cats, ferrets, civets, and dogs - had documented cases of COVID-19 infection. According to the analysis, there were no reports of infection in the other species: mice, rats, pigs, chickens and ducks.

For the study, researchers used computer modelling to test how SARS-CoV-2 uses its spike proteins to "infiltrate the cells of different animals."

The main point of entry on a cell's surface is the ACE2 receptor, according to researchers, which binds with the spike protein through a "lock-and-key mechanism" that helps the virus gain entry into the cells.

The study noted that there are "many different variants of ACE2" across different species and humans.

The researchers found that variants of the ACE2 receptor in humans followed by ferrets, cats, dogs and civets have the highest binding ability to the coronavirus spike protein, while mice, rats, chicken and ducks have "poor binding energy."

However, the study says binding affinity is not enough on it own to measure a cell's susceptibility to infection. The researchers also looked at the different species' codon adaptation index, which according to the study, is how efficient the coronavirus is at taking over a cell’s machinery once inside it.

The study reported that humans, chickens and ducks have the highest codon adaptation index, while the other species were "worse adapted."

When taking into account the binding affinity and the codon adaptation index, researchers concluded that the species most susceptible to COVID-19 are, in order, humans then ferrets, cats, civets and dogs.

CRG researcher and study author Javier Delgado noted that the analysis also found different variants of the ACE2 receptor in humans, which showed differences in the cell’s ability to bind to the coronavirus spike protein.

"We have identified mutations on the S-protein that dramatically reduces the capacity of SARS-CoV-2 to enter into the cell, protecting the host from catching COVID-19," Delgado said in the release.

He added that this may explain why some people suffer from severe COVID-19 symptoms while others exhibit few or none.

The researchers noted that understanding COVID-19 infectivity across different species can better inform public health measures to help reduce human contact with other susceptible animals.

Delgado explained that understanding how COVID-19 presents itself in other species may help avoid a possible prolongment of the COVID-19 pandemic as the virus mutates.

"We are now engineering mini-proteins from the human ACE2 protein to 'distract' the attention of the virus from entering cells and block an infection. Should new mutations of the viral spike protein arise, we could engineer new variants to block them," Delgado said.