Search to prevent next human pandemic

*Global Virome Project hunting for more than 1m unknown viruses
*Why bats carry diseases without getting sick, by researchers

To play good defense against the next viral pandemic, it helps to know the other team’s offense. But the 263 known viruses that circulate in humans represent less than 0.1 percent of the viruses suspected to be lurking out there that could infect people, researchers report in the Feb. 23 Science.

The Global Virome Project, to be launched in 2018, aims to close that gap. The international collaboration will survey viruses harbored by birds and mammals to identify candidates that might be zoonotic, or able to jump to humans. Based on the viral diversity in two species known to host emerging human diseases — Indian flying foxes and rhesus macaques — the team estimates there are about 1.67 million unknown viruses still to be discovered in the 25 virus families surveyed. Of those, between 631,000 and 827,000 might be able to infect humans.

The $1.2 billion project aims to identify roughly 70 percent of these potential threats within the next 10 years, focusing on animals in places known to be hot spots for the emergence of human-infecting viruses. That data will be made publicly available to help scientists prepare for future virus outbreaks — or, ideally, to quash threats as they emerge.

“It is ambitious,” says Peter Daszak, president of EcoHealth Alliance in New York City and a member of the Global Virome Project’s steering committee. But it’s more cost effective to head off pandemics than to deal with the aftermath, he says. “We believe we’re going to get ahead of this pandemic threat.”

Meanwhile, bats drink blood and dwell in caves, but they are perhaps most feared as vectors of disease.

While Ebola would kill a person within days, a bat could carry the virus for years without triggering any symptoms – transmitting it to humans along the way.

Now, for the first time, researchers have offered an explanation: the tiny flying mammals have the same immune pathway as humans, but it is dampened.

It means that pathogens trigger an immune response in humans that can prove fatal, but in bats their systems are tuned to such a low level that they are protected from disease but barely respond to it.

The secrets behind the vampire bats’ ability to survive on such an unusual diet – which is poor in nutrients and carries the risk of transmitting disease – has eluded scientists.

This week, researchers revealed new insight on the adaptations that opened the door to the bizarre diet, in what experts say is a ‘big evolutionary win.’

“Vampire bats have an ‘extreme’ diet, in the sense that it requires many adaptations in the organism,” lead author Lisandra Zepeda Mendoza, a biogeneticist at the University of Copenhagen, told AFP.

To better understand how these creatures are able to survive only on blood, an international team of scientists analyzed the genome of the common vampire bat along with its microbiome.

They discovered that the vampire bat’s microbiome is unlike carnivorous, insectivorous, and frugivorous bats.

Adaptations in the genome and microbiome linked with processes in metabolism and the immune system were dramatically different than the other species.

Vampire bats are equipped with a high number of protective bacteria, which produce antiviral substances to shield them from pathogens, they found.

The new study by Wuhan Institute of Virology in China is the latest in a recent slew of developments in bat research.

In 2016, scientists sequenced the bat genome for the first time, revealing that bats have the lowest number of interferons (virus-fighting proteins) of any mammal species, but that those proteins remain ‘active’ even when they aren’t diseased.

Earlier this week, Danish scientists revealed they had mapped the genome of the vampire bat to show that their unique microbiome allows them to live exclusively off blood without side effects.

Now, the Chinese team has looked at 30 bats from various sub-types to find that their STING-interferon pathway, present in all mammals, is unlike any other.

The STING (STimulator of INterferon Genes) pathway is overly heightened in humans with autoimmune diseases. It triggers an overt reaction to external elements in the body – or things the STING perceives as external elements – which cripples the sufferer.

Comparing bats with 10 other mammal types, including humans and cats and dogs, the researchers found the vilified creatures have the weakest STING of all, giving them an effective defense against disease.

“We believe there is a balance between bats and the pathogens they carry,” says senior author Peng Zhou.

“This work demonstrated that in order to maintain a balance with viruses, bats may have evolved to dampen certain pathways.”

He added: “In human history, we have been chasing infectious diseases one after another, but bats appear to be a ‘super-mammal’ to these deadly viruses.”

Zhou believes this is likely the result of the creatures evolving to be more resistant to disease, since they fly, have long lives and are exposed to many pathogens.

“Adaptation to flight likely caused positive selection of multiple bat innate immune and DNA damage repair genes,” Zhou suggested.