Bats are living up to their frightening reputation in the
world's worst Ebola outbreak as prime suspects for spreading the deadly virus
to humans, but scientists believe they may also shed valuable light on fighting
infection.
Bats can carry more than 100 different viruses, including
Ebola, rabies and severe acute respiratory syndrome (SARS), without becoming
sick themselves.
While that makes them a fearsome reservoir of disease,
especially in the forests of Africa where they migrate vast distances, it also
opens the intriguing possibility that scientists might learn their trick in
keeping killers like Ebola at bay.
"If we can understand how they do it then that could
lead to better ways to treat infections that are highly lethal in people and
other mammals," said Olivier Restif, a researcher at the University of
Cambridge in Britain.
Clues are starting to emerge following gene analysis, which
suggest bats' capacity to evade Ebola could be linked with their other
stand-out ability -- the power of flight.
Flying requires the bat metabolism to run at a very high
rate, causing stress and potential cell damage, and experts think bats may have
developed a mechanism to limit this damage by having parts of their immune
system permanently switched on.
The threat to humans from bats comes en route to the dinner
plate. Bushmeat -- from bats to antelopes, squirrels, porcupines and monkeys --
has long held pride of place on menus in West and Central Africa. The danger of
contracting Ebola lies in exposure to infected blood in the killing and
preparation of animals.
NATURAL HOSTS
Scientists studying Ebola since its discovery in 1976 in
Democratic Republic of Congo, then Zaire, have long suspected fruit bats as
being the natural hosts, though the link to humans is sometimes indirect as
fruit dropped by infected bats can easily be picked up by other species,
spreading the virus to animals such as monkeys.
This nexus of infection in wildlife leads to sporadic Ebola
outbreaks following human contact with blood or other infected animal fluids.
This no doubt happened in the current outbreak, although the
scale of the crisis now gripping Liberia, Sierra Leone and Guinea, which has
killed around 5,000 people, reflects subsequent public health failures.
"What is happening now is a public health disaster
rather than a problem of wildlife management," said Marcus Rowcliffe at
the Zoological Society of London (ZSL), which runs London Zoo.
Bats' role in spreading Ebola is probably a function both of
their huge numbers, where they rank second only to rodents among mammals in the
world, as well as their unusual immune system, according to Michelle Baker of
the Commonwealth Scientific and Industrial Research Organisation, Australia's
national science agency.
Baker, who is intrigued by bats' ability to live in
"equilibrium" with viruses, published a paper with colleagues in the
journal Nature last year looking at bat genomes. They found an unexpected
concentration of genes for repairing DNA damage, hinting at a link between
flying and immunity.
"(This) raises the interesting possibility that
flight-induced adaptations have had inadvertent effects on bat immune function
and possibly also life expectancy," they wrote.
UNDERSTANDING BATS
As well as tolerating viruses, bats are also amazingly
long-lived. The tiny Brandt's bat, a resident of Europe and Asia, has been
recorded living for more than 40 years, even though it is barely the size of a
mouse. Bats also rarely get cancer.
"We are just at the beginning," Baker said in a
telephone interview. "But if we can understand how bats are dealing with
these viruses and if we can redirect the immune system of other species to
react in the same way, then that could be a potential therapeutic
approach."
It won't be easy. Turning on components of the immune system
can bring its own health problems, but the idea -- which has yet to get beyond
the basic research stage -- is to turn up certain elements to achieve a better
balance.
One reason why Ebola is so deadly to people is that the
virus attacks the immune system and when the system finally comes back it goes
into over-drive, causing extra damage.
Ebola works in part by blocking interferon, an anti-virus
molecule, which Baker has found to be "up-regulated", meaning it is
found in higher levels, in bats.
VENISON, WITH WINGS
The bat immune system may or may not lead to new drugs one
day. Still, experts argue there are plenty of other reasons to cherish bats,
which also play a vital role in pollination and controlling insect pests.
They are also a traditional source of protein in West
Africa, often served in a spicy stew, and restrictions on bushmeat consumption
are now contributing to food shortages in parts of West Africa, according to the
International Food Policy Research Institute.
Hunting and butchering bats may be risky but cooking is
thought to make them safe. The World Health Organization advises animals should
be handled with "gloves and other appropriate protective clothing" and
meat should be "thoroughly cooked".
"In the long run it would be sensible to see people
moving away from hunting bats but in the short term they provide an important
source of food," said Rowcliffe of ZSL.
"Essentially, wild meat is a good, healthy product.
People in Britain eat venison and rabbit, and in many ways it's no different to
that."
