London, Dec 11 (IANS): Humans, followed by ferrets and to a lesser extent cats, civets and dogs are the most susceptible animals to SARS-CoV-2 infection, the virus behind the Covid-19 disease, say researchers.

The study, published in the journal PLOS Computational Biology, found that ducks, rats, mice, pigs and chickens had lower or no susceptibility to infection compared to humans.

"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," said study author Luis Serrano from the Centre for Genomic Regulation (CRG) in Spain.

"Our findings offer a clue for why minks - which are closely related to the ferret - are being infected by the disease, which is probably made worse by their packed living conditions and close contact with human workers," Serrano added.

Ten species were studied in this paper. Five species - humans, cats, ferrets, civets, and dogs - have had documented cases of infection by SARS-CoV-2. There are no reports of infection in the other five species - mice, rats, pigs, chickens and ducks.

The researchers used computer modelling to test how the coronavirus uses its spike proteins, which protrude from the surface of the virus, to infiltrate the cells of different animals.

The main point of entry on a cell's surface is the ACE2 receptor, which binds with the spike protein through a lock-and-key mechanism. There are many different variants of ACE2 within human populations and across different species.

Variants of the ACE2 receptor in humans followed by ferrets, cats, dogs and civets have the highest binding affinities to the viral spike protein, while mice, rats, chicken and ducks have poor binding energy.

However, binding affinity is not enough on its own to gage a cell's susceptibility to infection.

The researchers also tested the different species' 'codon adaptation index' - which is how efficient the coronavirus is at commandeering a cell's machinery once it has entered.

The more efficient the process, the better the coronavirus can create the proteins it needs to replicate. Humans, chickens and ducks have the highest codon adaptation index, while the other species are worse adapted.

Considering both binding affinity and the codon adaptation index, the researchers conclude that humans, followed by ferrets, cats, civets and dogs are the most susceptible animals to infection by coronavirus.