Horses and common livestock species unlikely to have a role in Covid-19’s spread – study

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This colorized transmission electron microscope image shows SARS-CoV-2 -the virus that causes COVID-19 —isolated from a patient in the United States. Virus particles are shown emerging from the surface of cells cultured in the lab. The spikes on the outer edge of the virus particles give coronaviruses their name, being crown-like. Credit: NIAID-RML, CC BY 2.0
This colorized transmission electron microscope image shows SARS-CoV-2 -the virus that causes Covid-19 — isolated from a patient in the United States. Virus particles are shown emerging from the surface of cells cultured in the lab. The spikes on the outer edge of the virus particles give coronaviruses their name, being crown-like. Credit: NIAID-RML, CC BY 2.0

Horses and common livestock animals are unlikely to play a role in the spread of Covid-19, the findings of fresh research suggest.

Scientists at Colorado State University have reported on pilot studies to evaluate the susceptibility of domestic livestock — cattle, sheep, goats, alpacas, rabbits and one horse — after infecting them with the SARS-CoV-2 virus via their nose.

None of the animals shed detectable infectious virus via nasal, oral, or fecal routes during the course of the study, while several individual animals — one calf, two goats, and one rabbit — showed evidence of viral RNA in nasal or oral swabs, which suggests these animals may be minimally permissive to infection.

Tests for neutralizing antibodies to the virus were low or non-existent one month after infection.

“These results suggest that domestic livestock are unlikely to contribute to SARS-CoV-2 epidemiology,” the study team concluded.

Live virus was found in the trachea of one calf three days after infection, but no other tissues were positive in that animal, suggesting local infection of the upper respiratory tract during acute infection.

Angela Bosco-Lauth and her fellow researchers said that while several animals developed low-level neutralizing antibodies within 14 days of infection, most were seronegative at the 28-day mark.

None of the animals displayed any clinical signs of disease or fever following inoculation, nor were any lesions consistent with SARS-CoV-2 infection identified.

The scientists said their results were consistent with other livestock studies demonstrating low-level viral replication in pigs, cattle and rabbits.

The researchers said the very small sample size was an obvious limitation of their study. “However, considering that other highly susceptible animals are readily infected, we believe these results provide sufficient evidence to exclude the species evaluated herein from the highly susceptible category.”

While all the species in the study were experimentally infected with an early isolate of the virus, the researchers said they did not have any reason to believe that newer human-adapted variants were any more likely to replicate in these poorly susceptible species.

Rather, they posit that domestic livestock is low-risk for participating in a spillover event or reverse zoonosis (infection of animals by humans).

This position, they said, is supported by the findings of a study comparing host range using the ACE2 protein sequence, in which binding likelihood of the virus in different species was predicted.

The lack of reports of any of the species assessed in their study becoming naturally infected in the first 18 months of the pandemic lends credibility to this position, the authors added.

“While there is much yet to be learned about the role of animals (wild or domestic) in the Covid-19 pandemic, including how the emergence of novel variants might impact non-human species, with each new study investigating the potential for animals to serve as reservoirs, we learn more about how SARS-CoV-2 behaves, and, perhaps, get closer to uncovering the answer to its origin.”

The study team comprised Angela Bosco-Lauth, Audrey Walker, Lauren Guilbert, Stephanie Porter, Airn Hartwig, Emma McVicker and Richard Bowen, all with Colorado State University; and Helle Bielefeldt-Ohmann, with the University of Queensland in Australia.

Angela M. Bosco-Lauth, Audrey Walker, Lauren Guilbert, Stephanie Porter, Airn Hartwig, Emma McVicker, Helle Bielefeldt-Ohmann & Richard A. Bowen (2021) Susceptibility of livestock to SARS-CoV-2 infection, Emerging Microbes & Infections, DOI: 10.1080/22221751.2021.2003724

The letter describing the study, published under a Creative Commons License, can be read here

 

 

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