How Ugandan tobacco farmers accidentally spread a bat-borne virus

How Uganda's tobacco cultivation unintentionally threatens the spread of bat-borne viruses

by rachel newer

zoonotic disease or disease transmitted from animals to humans, accounting for about three-quarters of new infectious diseases worldwide, including those that have the potential to lead to pandemics.of Risk of pathogens jumping from animals to humans This risk increases as humans encroach on ecosystems and disrupt interspecies relationships, but how that risk materializes in practice is unpredictable and difficult to understand. is.

a new paper published this week communication biology This study sheds rare light on one such case study. It's an example of how international demand for tobacco has led to habitat changes in Uganda, where chimpanzees and other species appear to have started consuming bat guano for mineral nutrients. In the process, the animals may have been exposed to more than 20 viruses, including a new relative of SARS-CoV-2, the pathogen that causes coronavirus.

“This is the butterfly effect of infectious disease ecology,” says study lead author Tony Goldberg, a wildlife epidemiologist at the University of Wisconsin-Madison. “A widespread event like the demand for cigarettes can have unexpected and unusual consequences for the emergence of diseases that we rarely see and follow unpredictable paths.”

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Goldberg and colleagues' research focuses on human-ecosystem interactions in the Budongo Forest Reserve in western Uganda. The first hint that something strange was going on came when researchers in Uganda noticed chimpanzees congregating in large hollow trees and eating something inside. Upon closer inspection, field researchers discovered that chimpanzees were eating bat guano. The bat guano was deposited by a colony of Noack roundleaf bats that roosted in hollowed-out trees.

Researchers have been observing chimpanzees at Budongo for decades, but no one had ever seen or heard anything like this before. So Goldberg and his colleagues set up on-site cameras near the tree. Videos they collected between 2017 and 2019 revealed 839 cases of guano ingestion by chimpanzees, as well as black and white colobus monkeys and red duikers.

Bat guano isn't the only seemingly strange thing that Budongo field staff and scientists have observed chimpanzees and other wildlife eating. Chimpanzees may also eat things like clay and termite mounds. The researchers found that this is because, like animals in many tropical ecosystems, animals living in Budongo face a lack of minerals in their diets.

So when observations of bat guano became apparent, Goldberg and colleagues immediately assumed it must be diet-related. But animals had never been observed eating guano before, so the researchers thought something in the environment must have changed. The story that emerged was more complex than they had imagined and hinged on the disappearance of a particular palm tree. raffia farinifera.

Over the past few years, chimpanzees and other animals have often been observed eating rotting wood from fallen trees. R. farinifera They searched palm trees for minerals. However, between 2006 and 2012, tobacco cultivation increased in this region.Local farmers started logging R. farinifera Use the strong, removable leaves of the tree to make strings to hang tobacco leaves to dry. Demand was so high that R. farinifera They have almost disappeared from Budongo.

“This removes a major source of minerals for the animals, forcing them to rely on other sources,” Goldberg said. Bat guano turned out to be a great alternative. Researchers don't know how chimpanzees and other animals learn to search for guano, but tests they conducted showed that the substance contains sodium, potassium, magnesium, and phosphorus. It was confirmed that there are many

However, since it was bat guano, Goldberg and his colleagues also wanted to test it for the virus. “Bats are amazing creatures. We love them. But they carry viruses,” Goldberg says. “We wanted to know what else chimpanzees get from this bat guano.”

Testing of 11 guano samples taken from hollow trees over an eight-month period in 2018 and 2019 revealed 27 types of coronavirus, including a “cousin” of SARS-CoV-2, Goldberg said. It is said that different viruses have been identified. Analyzes conducted by researchers to try to predict whether the new coronavirus can infect humans show that the new pathogen appears to attach to cells in a different way than SARS-CoV-2. It turned out that this was not the case. “We don't know enough about this type of coronavirus to predict what it will infect,” Goldberg said.

“The overarching theme that anthropogenic factors can drive ecological change and cause spillover of pathogenic viruses is very real, and this paper highlights additional interesting pathways by which this could occur. “We're emphasizing that,” says Rebecca Kaeding, a microbiologist at Colorado State University. Not involved in the research. “While this potential spillover pathway is still hypothetical, it is important to be aware of situations such as this one where the public health impact can be significant, but there are potential ways to mitigate this threat.” The solution could be as simple as providing farmers with the material to bind tobacco leaves to reduce pressure on R. farinifera wood. “

The new study raises further questions, including how widespread the phenomenon of chimpanzees and other species eating bat guano is. Although all the observations are from that one tree, Goldberg said there may be other examples of the behavior occurring elsewhere in Budongo and other mineral-poor ecosystems around the world. I'm guessing it's high. He also thinks that guano consumption may eventually be shown to be connected to the mystery of the origins of the Ebola virus.

Many scientists suspect that bats are the natural reservoir for the Ebola virus. Chimpanzees, red duikers, and black and white colobus monkeys are all species that have been implicated in various Ebola outbreaks due to human contact with them. “This paper may help lift the veil on a mystery that has puzzled disease ecology for decades. Wild animals like chimpanzees are infected with the Ebola virus in the wild, possibly from bats. How does it get infected?'' Goldberg said. “This is a lucky example of pulling back the curtain and seeing a hidden chain of events that could precede an outbreak.”