Bat coronaviruses silently infect tens of thousands of people each year, posing pandemic risk, study warns

Findings may aid surveillance programs in regions where bat viruses are more likely to jump to humans

There may be an average of over 65,000 cases of bat coronaviruses silently infecting people every year in Southeast Asia, according to a new study that could lead to new tools for improving preparedness against future pandemics.

The flying mammals are known to host coronaviruses that may be transmitted to people, including SARS-related coronaviruses.

Previous studies have suggested that transmission of these viruses to humans may be relatively common in some parts of the world.

However, human-bat interactions are also known to vary across regions, influenced by a variety of social, ecological, and economic factors at individual and community scales.

The research, published on Tuesday in the journal Nature Communications, used a new framework to estimate and map the risk of potential SARS-related coronaviruses spreading from bats to humans in Southeast Asia.

Researchers, including those from EcoHealth Alliance in the US, developed a method to assess the distribution and frequency of bat SARS-related coronavirus spillover risk in Southeast Asia.

They built prediction models for 26 bat species known to host SARS-related coronaviruses in the region that allowed them to map where human populations overlap with these bats.

Then scientists used disease prevalence and demographic data as well as risk assessments to calculate the number of people infected with SARS-related coronaviruses (SARSr-CoV) of bat origin in Southeast Asia every year.

Researchers estimate using the framework that a median of around 66,000 annual cases of SARS-related coronaviruses spillover to humans.

“Our estimate that a median of ~66,000 people are infected with SARSr-CoVs each year in Southeast Asia suggests that bat-to-human SARSr-CoV spillover is common in the region, and is undetected by surveillance programs and clinical studies in the majority of cases,” scientists wrote in the study.

Evidence of such silent undetected infections has also been demonstrated for other bat-origin viral infections.

Citing an example, researchers say the targeted surveillance of encephalitis patients in a small number of clinics in Bangladesh showed that the deadly Nipah virus causes outbreaks annually with an overall mortality rate of about 70 per cent, “despite it only recently being reported in the country”.

“Our calculation of undetected spillover represents the first published attempt, to our knowledge, to identify the spillover risk of SARSr-CoVs from bats to people,” researchers say.

Regions in southern China, northeastern Myanmar, northern Vietnam, and the “populous regions of Indonesia” have the highest diversity of SARSr-CoV bat host species, the study noted.

Scientists say many of these cases may be undetected due to limited surveillance, or because they might resemble other illnesses.

While more data is needed to validate these findings and to predict the transmission risk via intermediate hosts, scientists say the research could aid the design of surveillance and prevention programs in regions where these disease spillover events may be more likely to occur.

They say their assessment strategy of spillover risk of diseases jumping from animals to humans could be used as a tool for improving preparedness for emerging diseases of bat origin.

“These data on the geography and scale of spillover can be used to target surveillance and prevention programs for potential future bat-CoV emergence,” they wrote in the study.