Bats carry more viruses than thought | Science| In-depth reporting on science and technology | DW | 02.05.2012
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Science

Bats carry more viruses than thought

Bats play a key role in ecosystems and are threatened worldwide. But, new findings by German scientists indicate that bats also host a broad range of viruses - important for epidemiology and bat conservation.

Roundleaf bat in flight

Roundleaf bat in flight

A research team led by scientists at the University of Bonn in Germany has found that bats host a surprising range of viruses. Although most of the viruses are probably not communicable to us, some - such as mumps - are similar enough to be passed directly to humans.

Published last week in the journal "Nature Communications," the findings point to new research directions for virology, while including significance for how to fight the spread of disease. But bat conservationists are concerned about the effects of the study on protection for these flying mammals, which are in trouble around the world.

Broad spectrum

That bats and rodents can carry viruses has long been known. But the researchers discovered that whole families of viruses can hole up in bats.

"It shows bats have a significantly larger spectrum of viruses than any other mammalian order," said Christian Drosten, director of the University of Bonn's Virology Institute and lead author of the study.

Researchers testing nearly 5,000 bats found them to host a particularly large number of paramyxoviruses, a family that includes the viruses causing measles, mumps, and some kinds of colds, encephalitis and pneumonia.

The nearly 10,000 animals tested included 86 bat and 33 rodent species in Europe, Africa and South America.

Use of computational biology indicated that bats were probably "the ancestral host of ancestral paramyxoviruses," Drosten told DW, just as the flu originated in birds.

One mumps virus that bats carry is very closely related to that which infects humans. "Bats carry the sister, the brother, the cousins - the whole family" of mumps virus, Drosten said.

But Drosten emphasized that he didn't expect the vast majority of the tested paramyxoviruses to be transmissible to humans.

magnified rabies virus

The rabies virus has long been known to be transmissable from animals, including bats, to humans

Viral ecology

Last year, rinderpest - a virus related to measles - was declared eradicated.

The number of bat species tested by researchers in the current study comprises only 7.5 percent of the more than 1,200 worldwide.

Considering the vast array of viruses newly discovered to be on the reserve in bats, Drosten said "it's not unlikely" that they'll eventually encounter a reservoir of rinderpest in bats.

Drosten explained that just as caves, forests and attics make up the bat's habitat, host species' bodies are the "habitat" for virus strains.

And although vaccination may eliminate a virus in one host species, "cross-species transmission could occur as a result of a change of 'habitat,'" Drosten said.

"We've ignored pathogen ecology," he added, indicating new research directions for virology.

And while Drosten said that "it's always possible for a virus to jump species," he added that amongst the viruses they found in bats, "the vast majority are probably not communicable to humans."

While virologists consider ecology on a microscopic scale, bat conservationists expressed worry about the impacts of the study on bat species as a whole.

Ecologically important - and threatened

Andreas Streit, head of Eurobats - a United Nations conservation program, also based in Bonn - said bats are a "natural regulator of night insects, and they're also key pollinators and seed dispersers."

Due largely to habitat destruction and the so-called white-nose syndrome, "bats are threatened and declining around the world," Streit told DW.

Kiefer standing at the entrance to a cave

Andreas Kiefer of NABU checks the structural integrity of a cave

Andreas Kiefer, who heads up a bat conservation project in the neighboring Rhineland-Palatinate state, explained how habitat destruction is threatening bats, also in Europe.

Even as some species lack legal protection status in Europe, bats here have ever less safe places to live, including due to renovation projects that eliminate habitat in attics and eaves.

"For thousands of years, we've lived with bats literally under one roof," Kiefer told DW.

But Kiefer and Streit lament media reports they say have sensationalized the study's results, with conservation consequences for bats - which already get a bad rap.

Kiefer's conservation project, focused around one of the most significant regions for bats in Germany, includes efforts to involve the public in bat conservation, for example by promoting "bat boxes" that people can install around their homes.

After an online story published by Der Spiegel about the study called bats a "virus catapult," Kiefer says he's even gotten calls from the public, asking if they should take down their bat boxes to avoid getting ill.

Kiefer emphasized that as long as people aren't actually handling bats or their scat, they're extremely unlikely to come down with any infection.

Drosten added that the viruses found in European bats were not the most dangerous ones - those were reserved for the continent of Africa.

Potential for Africa

flying fox hanging upside-down in Ghana, 2011

Flying foxes are found in African tropics

Like mumps, nipah is a deadly virus that can be transmitted directly from bats to humans. Nipah was found to be carried by flying foxes, or species of large bats that live in the tropics.

"It's urgent to look for Nipah epidemics in Africa," said Drosten, and examine a possible connection with contact between humans and bats.

Bat species in Africa are hunted for meat, explained Streit - and not to feed starving people. "These bats are considered to be a delicacy," Streit said.

The hunting of bats as bushmeat in Africa "has to stop," Streit said. Aside from harming bat populations, the new findings indicate it could directly harm humans.

To this end, the UN's Food and Agriculture Organization has been attempting to inform people in the public health sector and governments about the problems with eating bats.

Drosten said "there's hope in the message" as well, as their discovery could also help develop new vaccines, for example in Africa.

Author: Sonya Angelica Diehn

Editor: Neil King

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