Can animals catch Coronavirus?

Is it possible for animals to become infected with SARS-CoV-2, and if so, which animals are most likely to be infected?

Worldwide infections with the novel SARS-CoV-2 virus have now exceeded 25 million, which shows the ease with which the virus spreads in humans. However, there have also been sporadic reports over the past six months that animals have been infected with the coronavirus. This is an important consideration both with regard to the spread of the disease and with regard to animals, which are a potential reservoir for the disease once its spread in humans has been contained.

A new study published in the Proceedings of the National Academy of Sciences of the United States of America (1) attempts to predict which animals would likely be suitable hosts for the coronavirus. To this end, research has focused on an angiotensin converting enzyme (ACE), specifically ACE 2. This enzyme serves as a target for the virus spike protein and provides an entry point for the virus into host cells. Studies of the virus have shown not only that it binds to ACE2, but also to the specific regions of the enzyme that it targets. The enzyme itself is a protein made up of a sequence of amino acids arranged in a specific order and spatial arrangement.

Could Animals Catch Coronavirus?

ACE 2 is highly conserved in mammalian species, which means that the sequence and structure are largely the same. This suggests that SARS-CoV-2 is theoretically capable of infecting a wide variety of mammalian hosts (suggesting that animals can catch coronavirus). However, this research goes a little deeper. It examines the exact sequences of ACE2 in 410 different vertebrate species. The species examined were mainly mammals (252), but also birds (72), fish (65), reptiles (17) and amphibians (4). The researchers focused on a specific 25 amino acid sequence that is believed to be the key region of the enzyme that the virus binds to. By comparing the similarity of this region to the human sequence, the researchers were able to predict how well the virus was likely to bind.

The different species were then classified according to how similar they were to the human sequence. For example, animals were given a classification of "very high" in cases where 23 or more amino acids matched the human sequence. Using this classification system, the 18 species at greatest risk of infection with SARS-CoV-2 were all primates. The next level species included dolphins and whales, some deer species, and some rodents. Many of the more domesticated species such as cats, cattle, and sheep scored intermediate ratings.

The researchers also looked at variations in the structure of the binding site. Identical amino acid sequences can be arranged slightly differently in 3D space and this can affect the binding of the virus. They first looked at how the structure of the binding site varied between people and found that significant variations were rare. When examining the structural variation in animal ACE 2, however, they found that certain mutations that increase the binding capacity of SARS-CoV-2 occur more frequently and are subject to positive selection.

This study will benefit from the emergence of greater knowledge of the effects of mutations in ACE2 on SARS-CoV-2 binding. Further research is required in this area, which in turn would strengthen the predictions of the algorithm used here. Overall, however, the study highlights an important aspect of the SARS-CoV-2 virus. It gives us a good indicator of which animals are most likely to be infected with coronavirus, and also highlights the most likely intermediate species that facilitated the spread of the virus from bats to humans.

Written by Michael McCarthy

1. Damas J., Hughes GM, Keough K.C., Painter CA, Persky NS, Corbo M. et al. Broad host spectrum of SARS-CoV-2, predicted by comparative and structural analysis of ACE2 in vertebrates. Procedure of the National Academy of Sciences. 2020: 202010146.

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