The tiger and the elephant and the polar bear may be stars at the Buffalo Zoo, but it was a humble wallaby that helped scientists prove that the family of viruses that gave rise to Ebola is tens of millions of years old, not a mere 10 millennia, as was previously supposed.
The determination was made in recent years by scientists at the University of Buffalo who tested wallaby hair from the zoo along with a brown bat snared on campus to confirm what they had identified in existing databases for the first time: The genetic material of various small animals contains “fossil” fragments of filoviruses, the family that includes Ebola and Marburg.
“Who knew that the bats in the attic as well as modern marsupials harbored fossil gene copies of the group of viruses that is most lethal to humans?” co-author Dr. Derek Taylor said when the paper was published in BMC Evolutionary Biology in 2010. “Our findings demonstrate that filoviruses are, at a minimum, between 10 million and 24 million years old, and probably much older.”
Unlike other viruses such as HIV, the filoviruses lack the capacity to create their own DNA and were therefore assumed to be incapable of inserting themselves into a host’s genetic makeup.
Taylor and his co-authors, Dr. Jeremy Bruenn and Dr. Robert Leach, came upon the fossils by chance during a more general database search.
“It was a fortuitous discovery,” Bruenn told The Daily Beast last week. “I was looking for all viral genomes, and that’s what I found.”
The mammal profiles in the genetic databases included the wallaby, and the scientists decided to verify their finding by looking directly at the animal’s DNA. They asked the director of the Buffalo Zoo for some wallaby hair.
“We didn’t want to hurt the wallaby,” Bruenn says. “They shed hair.”
The zoo is blessed with multiple wallabies and was happy to oblige. The scientists were able to extract sufficient DNA from the roots, and they did indeed find the virus fossils. They got the same result from the campus bat.
Among the other small mammals studied in the databases were two rodents, the house mouse and the Norway rat, that diverged evolutionarily some 12 million years ago. And yet they proved to have the same virus fossils in the exact same chromosome amid billions of possibilities.
The finding suggested that the evolutionary roots of Ebola and its cousins predate the divergence, giving the filoviruses an absolute minimum age far older than the prior estimate, which had been made via mutation rates. The previous guess had been 10,000 years, around the time agriculture emerged. (The earliest fossils of anatomically modern humans are from about 200,000 years ago.)
“Instead of having evolved during the rise of agriculture, they more likely evolved during the rise of mammals,” Taylor said in 2010.
One remaining question was how those fossils got there when these particular viruses had been presumed to lack the capacity to insinuate themselves into an animal’s genetic makeup.
One possible answer was that the animal integrated fragments of the virus into its genes as a result of persistent infection.
This, in turn, raised the possibility that in the course of continued evolution, the mammals had incorporated the fossil as a genetic defense against the viruses—a kind of vaccine generated by natural selection.
And that could now help us in developing our own defenses against a virus for which there is presently no proven treatment.
The results also may accord insight into which animals might serve as hosts for Ebola, carrying the virus with no manifest ill effects.
“The reservoir for filovirus has remained a huge mystery,” Bruenn said in 2010. “We need to identify it because once a filovirus hits humans, it can be deadly.”
Bruenn’s words are now proving all too prescient.
But he and his colleagues are true scientists who prize knowing over being known, and they are not seeking public acclaim now that Ebola is in the headlines.
Bruenn suggested that he spoke to The Daily Beast only because he happened to pick up the phone. He is no lover of attention, and Taylor is said to be even less so, though one photo suggests he does like wallabies.