Coronavirus: Don't scapegoat bats yet, says Scottish scientists' study

It is common for deadly and newly emerging viruses to circulate in wild animals and insect communities long before they spread to people. Most of the major pandemics of the last 100 years began in animal hosts, including the Spanish flu which jumped from birds to humans and HIV, which came from chimps.

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Since Huanan Seafood Wholesale Market in Wuhan, China, was pinpointed as a possible point of origin for coronavirus in late 2019, it has since infected more than a million people across the globe.

It has been suggested that pangolins – a scaly mammal that looks like an anteater – was a staging post for the virus before it spread to humans.

But new research suggests bats are no more likely to pass on viruses to humans than other animals.

The research, led by scientists at the University of Glasgow reveals 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 published to in the journal Proceedings of the National Academy of Sciences of the United States of America suggest previous scientific thinking that certain animals pose a heightened risk of spreading viruses to humans may not be correct.

The researchers say that the findings cast doubt on the idea that bats produce viruses with a "heightened propensity" to infect humans.

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."

Dr Streicker added:"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."

The study, funded by Wellcome, The Royal Society and The Medical Research Council, found that the likelihood of a virus transmitting from animals to humans does not significantly differ across 11 different types of bird and mammal.

Instead, scientists now believe that it is the characteristic traits of the viruses, rather than their animal hosts, that will be the more useful in predicting whether the virus will be transferred to humans.

Dr Nardus Mollentze, research assistant at the university's 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 Ebola viruses, 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.

"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."

A year-and-a-half before the current Covid-19 pandemic, Dr Streicker led a study that showed that machine learning algorithms could predict the natural host of a virus and might help prevent the spread of disease to humans.

Identifying the natural virus hosts early - which can help prevent the spread to humans - can take years of intensive field research and laboratory work.

Those delays make it difficult to implement preventative measures, such as vaccinating animals or preventing contact between species.

But he led a group of scientists that found that a new machine learning algorithm could accelerate this process.

An algorithmic model accurately predicted the likely host for a broad spectrum of single-source RNA viruses - the viral group which jumps from animals to humans most often.

The researchers were able to train machine learning algorithms to match the patterns within viral genomes to the animal they came from. When a virus jumps from a natural host to a human, it leaves a fingerprint from the animal or insect which can be traced back.

Over 500 viruses were studied, and in over 70 per cent of cases the model correctly predicted the known natural host of the disease. In 97 per cent of cases, the tool determined whether or not the virus was transmitted by blood-sucking insects, and the type of insect was predicted correctly about 90 per cent of the time.

The model also revealed new leads. Ebola was also thought to have come from bats, but when the team tested two of the four strains of the disease, they found strong evidence that these strains of the virus could also have originated in primates.

The team were developing a web application to allow scientists across the globe to submit their virus sequences and recieve predictions for natural hosts and disease transmission routes within minutes.

And late last year Dr Streicker was among a group of scientists who pioneered a new technique to help stop the spread of deadly rabies from infected bats to humans.

The group 'glowing' fluorescent gel to estimate the potential effectiveness of spreadable vaccines to control diseases in wild bats in South America.

Rabies vaccines given to bats can be transferred from one bat to another - however how widely they were spread was not previously known.

The fluorescent gel - called Rhodamine b - was applied to bats in three colonies in Peru, where it acted as a marker to simulate the bat-to-bat spread of an oral rabies vaccine.

When the gel was ingested by bats that groomed each other, it led to fluorescence in the bats' hair follicles, which was then monitored by fluorescent microscopic analysis of hair samples collected by the scientists.

Where common vampire bats routinely feed on human blood, rabies is estimated to cause up to 960 deaths in eve-ry 100,000 people, while losses from livestock mortality exceed £38.61 million annually, disproportionately affecting impoverished, rural communities.