Stunning bat cave footage captures disease spread risk for first time

Researchers in Uganda have discovered a complex network of animals feeding on bats infected with Marburg virus, for the first time capturing startling footage of potential spillover risks.

The observations, caught on camera traps placed outside the entrance to “Python Cave” in Queen Elizabeth National Park in western Uganda, are the first confirmation “of a dynamic, multispecies exposure network at a known Marburg virus site”, the researchers say.

In a preprint of their findings, they write that the discovery of so many animals feeding on the bats “may represent a Rosetta Stone for interpreting the real-time mechanics of zoonotic spillover”.

Over a five-month period between February and June last year, the researchers recorded at least 14 different vertebrate species visiting the cave to feed on the bats, including leopards, several species of primate, birds of prey and monitor lizards.

In one clip, an adult leopard can be seen approaching the entrance to the cave, swiping at the bats as they fly out in huge numbers before leaving with one in its mouth.

Other footage captured at the site in the Maramagambo Forest showed a troop of monkeys feeding on the bats, along with civet cats and genets, another small mammalian predator.

The cave is home to an estimated 56,000 Egyptian fruit bats and is situated in an area that has long been important to the study of Marburg, a close cousin of Ebola.

The virus can have a fatality rate as high as 90 per cent and, while there are several vaccines in development, none has yet been approved.

In 2008, a Dutch tourist who visited Python Cave caught and died from Marburg. An American tourist also fell ill with the disease after visiting the cave but survived.

And in 2009, scientists from the US Centres for Disease Control and Prevention (CDC) isolated Marburg virus for the first time from fruit bats found in a nearby cave.

The camera traps were originally placed at the cave as part of a project to gather data on lions and hyenas living in the Queen Elizabeth National Park.

Orin Cornille, a field co-ordinator at the Kyambura Lion Project, said it was a surprise to capture so many different species feasting on the bats, about 7 per cent of which are known to carry Marburg.

“What surprised me is we were seeing blue monkeys, baboons, vervet monkeys, going in there and snatching bats. From a virological standpoint, I think that’s the crazy part.

“The leopard is really cool, and all the genet cats and the civets – and all the different avian species are really cool to watch. But I think from a virus point of view, it’s probably the monkeys which are the scariest thing.”

The researchers were keen to stress that they had seen no evidence of actual spillover.

“This could be something that’s been taking place for millennia – the Rift Valley and the Albertine Rift, these are ancient systems,” said Alexander Braczkowski, scientific director at Kyambura Lion Project.

“We are seeing a lot of the same species, and, in fact, some of the same individuals going to this cave and feeding, you know, for months and months and months on end.”

One particular leopard that visited the cave repeatedly over the five-month period was caught on camera eating numerous bats. It was given the nickname Akahaya, a term in a local language meaning “untouchable”.

The researchers hope that their findings can be the starting point for further investigation into spillover risks.

“For one of the first times in nature, there’s essentially a site where you have the ability to repeatedly see animal interactions between the filovirus reservoir and then these predators, clearly mixing body fluids – eating each other,” said Braczkowski.

“We’re going to be working with some collaborators in future to potentially try and map out more of this whole interface, and figure out if animals are getting infected,” he said.

Bosco Atukwatse, another field coordinator at the Kyambura Lion Project, first had the idea to install cameras by the cave.

He told the London Telegraph that features of the cave made it uniquely suited to predators hoping to score an easy meal.

The entrance to the cave is partially sunken and low to the ground, while piles of guano – bat droppings – that have accumulated over years, means even smaller animals can get to the bats.

“A monkey can just stand on two legs and grab a handful of bats and run away with it,” he said, adding that it was not always clear where the dead bats ended up.

While bats are thought to be the main reservoir for the virus in the wild, and can carry Marburg without falling sick, there is evidence to suggest that other animals, including some primates, can spread the virus after interacting with bats.

‘Spillover crucible’

The researchers described the cave as a “spillover crucible”, noting that many of the species they observed preying on the bats are themselves eaten by humans as bushmeat.

“There are very many pathways through which a disease of international concern can actually spread to a population unnoticed,” Atukwatse said.

The camera traps also recorded an estimated 400 humans visiting the cave “including school groups, tourists, and local trainees – the majority with no personal protective equipment”.

Braczkowski, the scientific director and one of the paper’s authors, said the Ugandan authorities were well aware of the risk posed by the site, and had put in place signs warning of the danger and installed a viewing platform about 40 metres from the cave.

The researchers’ findings add to a growing body of evidence documenting previously unseen interactions between animal species that are shining light on zoonotic risks.

Last year, researchers in Germany documented rats preying on bats for the first time, raising concern about pandemic risks.

In their report, however, the researchers who focused on Python Cave note that much of what we think we know about zoonotic spillover is still largely theoretical – the documentation of complex interactions between multiple species at known zoonotic reservoirs “remains exceptionally rare”.