The virus that causes Covid-19, SARS-CoV-2, is zoonotic — meaning it can be both carried and transmitted by animals.
New findings reveal which animals are most and least at-risk for the virus behind the ongoing global pandemic.
In a new genomic analysis, researchers compared 252 mammal species to gauge how likely they are to become infected with SARS-CoV-2. To do this, they studied a specific cellular receptor, the ACE-2 enzyme, which is one of the key factors needed for a virus to bind to and enter a cell.
The researchers also looked at birds, reptiles, fish, and amphibians, analyzing 410 vertebrate species in all. But only mammals fall into the medium to very high risk categories — and only primates fall into the highest-risk category. That suggests those species — humans included — are at highest risk for SARS-CoV-2 infection, the researchers say.
Here is how some of the mammal findings break down:
Very high risk:
- Western lowland gorilla
- Rhesus macaque
- American bison
- Grizzly bear
- Giant panda
Very low risk:
The animals were compared with humans to determine their risk. Within humans' ACE-2 receptors, 25 amino acids are needed for the SARS-CoV-2 spike protein to bind to cells. The researchers theorize that an animal's risk level depends on how much that animal differs from humans.
The new study was published on August 21 in the journal Proceedings of the National Academy of Sciences.
Animal risks — In all, roughly 40 percent of the species potentially at risk for SARS-CoV-2 are also classified as "threatened" by the International Union for Conservation of Nature, the authors report.
The link may not be a coincidence.
Previous research has gotten into the reasons behind why some animals are more susceptible to viruses than others.
It's a common belief that rats and bats, for instance, are prime carriers of viruses. But that's not to do with the animals' biology so much as how much humans come in contact with them, an April 2020 data analysis showed. In fact, scientists determined that bats and rodents are "unexceptional" when it comes to transmitting the virus. But they do come into contact with humans, especially as we push further into animals' habitats, increasing the odds of a virus making the leap from animal to human.
The researchers on this new study follow the same thread. They highlight the animals that are at highest risk for SARS-CoV-2 and are endangered, a status that typically comes as a result of humans moving in and habitat destruction.
"These species represent an opportunity for spillover of SARS-CoV-2 from humans to other susceptible animals," the authors write.
The new study was designed to get closer to identifying intermediate hosts for SARS-CoV-2, and thus reduce the chance of future outbreaks, they write.
"The data provide an important starting point for identifying vulnerable and threatened animal populations at risk of SARS-CoV-2 infection," lead Harris Lewin, a professor of evolution and ecology at UC Davis, said in a statement. "We hope it inspires practices that protect both animal and human health during the pandemic."
Abstract: The novel coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of COVID-19. The main receptor of SARS-CoV-2, angiotensin I converting enzyme 2 (ACE2), is now undergoing extensive scrutiny to understand the routes of transmission and sensitivity in different species. Here, we utilized a unique dataset of ACE2 sequences from 410 vertebrate species, including 252 mammals, to study the conservation of ACE2 and its potential to be used as a receptor by SARS-CoV-2. We designed a five-category binding score based on the conservation properties of 25 amino acids important for the binding between ACE2 and the SARS-CoV-2 spike protein. Only mammals fell into the medium to very high categories and only catarrhine primates into the very high category, suggesting that they are at high risk for SARS-CoV-2 infection. We employed a protein structural analysis to qualitatively assess whether amino acid changes at variable residues would be likely to disrupt ACE2/SARS-CoV-2 spike protein binding and found the number of predicted unfavorable changes significantly correlated with the binding score. Extending this analysis to human population data, we found only rare (frequency <0.001) variants in 10/25 binding sites. In addition, we found significant signals of selection and accelerated evolution in the ACE2 coding sequence across all mammals, and specific to the bat lineage. Our results, if confirmed by additional experimental data, may lead to the identification of intermediate host species for SARS-CoV-2, guide the selection of animal models of COVID-19, and assist the conservation of animals both in native habitats and in human care.