The virus hunters who search bat caves to predict the next pandemic

EcoHealth Alliance's team take samples from a bat. Over the past decade, they have collected 15,000 bat samples.

Predict operates in 31 countries. Another team of virus hunters, belonging to the Smithsonian Institution, has started focusing on Myanmar and Kenya. "So far, we were able to identify six novel coronaviruses in Myanmar," says Suzan Murray, who leads the Smithsonian Institution's Global Health Program.

"These are areas with lots of wildlife biodiversity, a growing human population encroaching on the natural habitat, good travel networks and a large amount of livestock, which means there is a high potential for virus spillovers between species," says Dawn Zimmerman, who leads some of the Smithsonian Institution's virus sampling expeditions.

Bats to humans

Southeast Asia and China are of particular interest as large swathes of their populations make regular contact with wildlife, by hunting it, selling it -- often live -- in wet markets and eating it, according to Daszak.

After analyzing blood samples of people living near two bat caves in Jinning County, Yunnan province in 2015, Daszak's team found that 3% had antibodies for viruses normally only found in bats -- meaning they had already been exposed to them.

"They might have unknowingly contracted these pathogens and recovered or only had a few body cells infected," he says.

To make the jump to humans, coronaviruses need to be able to bind to their cell receptors, which usually requires an intermediate animal host, explains Wang. This can be a civet cat, a camel, a pangolin or another mammal closely related to humans, he said.

But they usually originate in bats, which carry an extremely high proportion of viruses capable of infecting humans, such as Marburg, Nipah, Ebola and SARS, according to Daszak, who co-authored a study in Nature on this topic in 2017.

"Because bats are flying mammals, their body is exposed to a lot of stress, which would normally generate an immune system response," he explains. "To deal with this, they have to tone down their immune systems, which in turn makes them more susceptible to viruses and capable of tolerating a higher viral load."

Bats also make up roughly 20% of all mammal species and congregate in huge colonies in crowded caves, making the spread of viruses among them more likely.