A virus watchlist which gives pathogens a “credit rating”, much like those used by banks insurance companies, has been developed to flag high-risk diseases with the potential to jump from animals to humans and cause another pandemic.
It is estimated that birds and mammals harbour roughly 1.7 million viruses, including some 700,000 with “zoonotic potential” – meaning they could spread to people.
But after identifying almost 900 new potentially dangerous viruses – including 16 coronaviruses – over the last decade, experts have been left with a difficult question: which pose the greatest risk to humans?
A new app called SpillOver is an attempt to categorise that risk and identify “disease X” before it strikes.
The web-based tool ranks 887 viruses based on 31 indicators, to identify those most likely to make the jump from animals to humans. The viruses with the highest ratings include Ebola and Lassa Fever, both hemorrhagic diseases, but the list also includes almost 850 previously unidentified pathogens.
“Motor insurance companies run algorithms to work out if you’re more likely to have a car crash or not, while money lenders can assess whether you’re more likely to get into debt,” Dr Zoe Grange, who worked on the project as a postdoctoral ecologist at the University of California at Davis, told The Telegraph.
“We decided to try and emulate this, to create a credit report for viruses. The aim is to use the risk assessment to predict if they’ll spillover into people and identify which viruses warrant further research,” Dr Grange, now lead health protection scientist at Public Health Scotland, added.
The watchlist that emerged is not a measure of whether a virus has the ability to infect humans, but instead the opportunity a given pathogen has to spillover from animals to people.
This is calculated based on a range of factors – which are outlined in a study published in PNAS journal – including the number of species the virus is found in and whether the pathogen has been detected in an area or animal in close proximity to humans.
“This is the first step in dealing with a big gap in our ability to predict pandemics,” said Dr Peter Daszak, president of the EcoHealth Alliance – a partner behind SpillOver – and a member of the World Health Organization’s investigation into the origins of Sars-Cov-2.
He added that the watchlist was in development long before Covid-19 emerged, but the pandemic has shone a spotlight on the need to better prepare for future outbreaks – which are inevitable.
Known zoonosis, unsurprisingly, topped the list, which included pathogens from 25 different viral families.
Sars-Cov-2 ranked second – with a risk score of 87 out of 155 – behind Lassa virus, a sometimes deadly hemorrhagic fever endemic in rodents in west Africa. Other high risk viruses in the top 10 include Ebola, rabies and Nipah, which can cause fatal encephalitis.
Researchers said they expected Covid-19 to pinch the top spot in due course, as more information about how it spreads from animals to humans emerges.
A joint WHO-China has concluded it is most likely that the virus emerged from bats, via an as-yet-unknown intermediary animal. SpillOver was therefore reliant on limited data tracing Sars-Cov-2 in zoo tigers, lions and mink, but researchers say it’s high presence on the list demonstrates the algorithm behind the watchlist works.
Several newly detected viruses rank above known zoonoses. This includes a pathogen provisionally known as PREDICT_CoV-35 – named after a $238 million project funded by the United States between 2009 and 2019, to take samples from high-risk wildlife.
“Broad host and virus geography combined with detection in bats at high-risk disease transmission interfaces, including hunting and within human dwellings, suggests that PREDICT_CoV-35 is of high public health relevance,” the PNAS report warned.
It added that while the virus has not yet been identified in humans, it’s possible that it has made the jump already.
“Spillover events may be going unrecognised due to lack of diagnostic capabilities and underreporting, as well as the propensity of coronaviruses to cause only mild symptoms or asymptomatic cases,” the authors wrote.
The team hopes the SpillOver web-app – which can be constantly updated as new data emerges – will be used by policy-makers and funders to target future research into whether viruses with the greatest opportunity to infect humans have the capacity.
“We’ve identified the viruses, but don't know if they can actually infect humans. That’s the next stage of research,” said Dr Grange. “More lab tests of high risk viruses through collaboration with different disciplines, from serological testing to genome sequencing, to fill in the data gaps.”
The tool could also encourage interventions to reduce the chance of a spillover event taking place at all, from closing access to a bat cave to removing host species from a food chain or educating local communities of the risks associated with close contact to wildlife.
“All of these strategies would have helped reduce the potential for Sars-Cov-2 to emerge,” said Dr Daszak. “The important thing is that this is used in the future.”
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