The idea that certain creatures such as bats pose a higher risk of spreading viruses to humans may not be accurate, new research suggests.
Scientists have found that the risk of zoonotic viruses – diseases that spread from animals to infect humans – spreading to people is largely the same across diverse groups of animals.
The findings cast doubt on the idea that bats, thought to have been the origin of the coronavirus SARS-CoV-2 which led to the current pandemic, produce viruses with a “heightened propensity” to infect humans.
The study, led by the University of Glasgow, found that the proportion of zoonotic viruses does not differ significantly across 11 major orders of birds and mammals.
Scientists now believe that it is the characteristic traits of the viruses, rather than their animal hosts, that will be the more useful predictors of zoonotic transmission.
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Dr Daniel Streicker, senior research fellow at the Institute of Biodiversity, Animal Health and Comparative Medicine at the University of Glasgow, said: “The recognition that several high-profile viruses originated from bats triggered tremendous interest in whether there was something special about their ecology or immune systems which makes their viruses disproportionately likely to infect humans.
“Our finding that the number of zoonoses that have emerged from bats is about what would be expected for any mammalian group of their size casts doubt on the idea that traits of bats produce viruses with a heightened propensity to infect humans.
“To know if there is anything special about bats, we now need to understand whether the bat viruses that do jump to humans cause more severe disease or spread better among humans than viruses from other animals, which is currently uncertain.”
Wondering why bats have so many zoonotic viruses? Our latest suggests a numbers game – no evidence of disproportionate zoonotic risk from any bird or mammal group, but reservoir groups with more species have more viruses and more zoonoses @NardusMollentze https://t.co/kwuyaalecS
— Daniel Streicker (@DanielStreicker) April 13, 2020
The study was led by the MRC-University of Glasgow Centre for Virus Research and the Institute of Biodiversity, Animal Health and Comparative Medicine at the University of Glasgow and is published in Proceedings of the National Academy of Sciences.
Dr Nardus Mollentze, research assistant at the Centre for Virus Research, said: “Although bats will and should remain a focus for viral reservoir research, as the likely origins of major zoonotic pathogens such as SARS-CoV-2 and Ebolaviruses, our work shows that the proportion and number of zoonotic viruses in bats is not unusual compared to other mammalian groups.
“This means that ongoing efforts to identify potential future threats to human health by screening animals for undiscovered viruses will need to focus on a much wider range species than is currently the case.
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“Our study also highlights the need to find new traits of viruses that can help us anticipate their zoonotic potential, since knowledge of the current reservoir was not helpful to predict whether a virus might infect humans – even when the reservoir is closely related to humans.”
The research work was funded by Wellcome, The Royal Society and The Medical Research Council.
Reader Q&A: Can my dog get coronavirus?
There have so far been two cases of dogs testing positive for the coronavirus, both in Hong Kong for dogs whose owners were hospitalised with COVID-19. The tests used on the dogs are the same as those used on people: nasal and oral swabs that test for the genetic material of the coronavirus.
However, both dogs had very low levels of the virus, and it’s not clear if they were infected or had just breathed in contaminated air. Neither dog showed any signs of illness, nor any immune response. If they were infected, then it was a very minor infection.
It is theoretically possible for our dogs and cats to become infected by the coronavirus, but the science suggests that it’s very unlikely. The virus would have to be able to replicate well in our pets, for which there’s no evidence, and it’s also rare for a virus to jump to a different species.
That said, pets do pose a risk of transmission if someone touches an animal that belongs to someone with COVID-19. Because of this, people who have symptoms of COVID-19 are advised to limit their contact with pets and wash their hands before and after interacting with them. For everyone else, keep regularly washing your hands and practise physical distancing, from people as well their pets.