Bats may provide answers on Ebola

Posted: August 13, 2014

When DeeAnn Reeder, a Bucknell University biologist, provoked the immune system of fruit bats, an odd thing happened.

Most animals that have been studied get a fever when injected with the portion of bacteria she used. The bats got colder.

"Bats are different," said Reeder, who studies them both here in Pennsylvania and in South Sudan, one of the places where Ebola first emerged.

Just how they are different is suddenly a hot topic.

A long list of viruses that are deadly to people and sometimes other animals - Ebola, Marburg, rabies, MERS, SARS, Nipah and Hendra - have something in common: They seem to originate in bats. Even diseases such as hepatitis C and measles are likely descendants of bat bugs.

With the exception of rabies, these vicious viruses don't seem to bother the bats much at all.

As Ebola rages in West Africa, with more than 1,000 dead so far, bat biology and its role in spreading emerging diseases with huge destructive potential has moved up the scientific priority list.

A key question is whether something about the bat immune system allows it to coexist with viruses more easily than other animals. If so, can we harness that to make better treatments?

"We'd love to figure it out because it might open the door to new therapies," said Christopher Broder, a virologist with Uniformed Services University of the Health Sciences in Bethesda, Md.

Some scientists recently hypothesized that bats respond to viruses differently because they are the only mammals that fly, a feat that raises their body temperature and creates huge demand for energy. One theory is that they can repair their DNA more quickly than other mammals because the exertion level is damaging.

"Even the authors of that paper admit that it's rampant speculation," said Reeder, who is intrigued, nonetheless.

Reeder will now study whether bat immune systems change during different times of year, during pregnancy, or when food is scarce. That might help predict when they are most likely to shed viruses that could spill over into other animals.

She wants to look at the bat transcriptome, a record of every gene expressed in an animal at a given time. Again, the goal is to see how the immune system changes.

She and other scientists said efforts to understand bats have been hampered by lack of funding and chemical tools.

Of course, other mammals spread diseases - rodents, for example, give us hantavirus, a respiratory illness that kills about half its human victims - but there is some evidence that bats carry an unusual number of viruses. The 1,200 known bat species carry at least 15 different virus families, Reeder said. Most are harmless.

Bats might have more viruses simply because they are ancient creatures that have had lots of time to learn to live peaceably with pathogens. Now they are exposing human bodies to viruses humans have never encountered before.

Whatever the explanation for their role in emerging diseases, scientists say the problem is not so much bats as it is people.

"These viruses spill over because of things we're doing to the environment," said Jonathan Epstein, a veterinary epidemiologist with the scientific organization EcoHealth Alliance. "I certainly don't want to vilify bats."

The viruses spread from bats to people when we encroach on their territory and come into contact with their saliva, urine, feces, or uncooked meat. (Bats are eaten by humans in parts of Africa.) Bats also infect other animals that then spread germs.

Bats eat large numbers of insects or pollinate fruit trees and spread seeds. Killing them is not a solution.

"If you eliminate bats, you'll screw up the whole ecosystem," said Broder, the virologist.

The cute little insect-eating bats that live around here carry rabies, but not the headline-grabbing emerging viruses that the United States has largely avoided so far. They are themselves in danger from a fungus that attacks them while they hibernate. Most of the newer diseases have been traced to various species of fruit bats.

No one knows how the current Ebola outbreak - now deemed an international public health emergency - started. But most of the spread has been not from fruit bats, but person to person because of inadequate infection-control measures.

In a world where we are only a plane ride or two from any viral hot spot, ignorance and poverty have transformed Ebola from a disease that once burned out quickly in isolated villages to a world threat. Other bat-borne diseases have similar potential.

"Can you imagine if one or two [infected] people in West Africa managed to get a ticket back home and their home was New Delhi, India?" Broder said. "That would be 10 times worse than what's going on in Africa."

Broder is an expert on Nipah and Hendra, related viruses (measles, mumps, and canine distemper are in the same family) that cause severe respiratory and neurological symptoms. They are spread by big fruit bats known as flying foxes. Hendra spread from bats to horses and then to people in Australia. Broder helped develop a vaccine that has been given to 130,000 Australian horses.

In Malaysia, Nipah spread from bats to pigs that were being raised on huge farms near orchards. The pigs gave the virus to people. There has been human-to-human transmission in Bangladesh, where people initially caught the disease after bats contaminated date palm sap, which is sold as a drink.

"Nipah clearly has the potential to be a pandemic," Broder said.

Luckily, Ebola is relatively hard to spread. Doctors feel confident that they can control it if patients unwittingly bring it to the U.S. Still, scientists say it's in our best interest to learn more about bats - and help developing countries get the tools and education they need to prevent and contain outbreaks - to avoid even bigger problems in the future.

"The next thing that emerges from the forest may be worse," Reeder said.


sburling@phillynews.com

215-854-4944

@StaceyABurling

www.inquirer.com/health_science

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