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 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.
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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."
(Editing by Peter Millership and Giles Elgood)
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