Bats are hosts to the deadliest viruses we know, but far from infecting humans they may actually hold secrets to improving our health and longevity

Roosting jam-packed together increases the spread of pathogens 167/Joel Sartore/Ocean/Corbis

EMMA TEELING loves bats. She is so keen on them that she has spent the past three summers clambering around Gothic churches in Brittany searching for greater mouse-eared bats under dusty eaves and in dark bell towers. She is aware that others do not share her passion. Bats have been demonised throughout history and across cultures. For most of us, Teeling’s little furry fliers are the crepuscular creatures of folklore, witchcraft and horror stories.

Indeed, the dread instilled by bats has only increased in recent years, with the discovery that they harbour the viruses that cause Ebola, SARS, MERS and other so-called emerging infectious diseases. Often fatal in humans, an outbreak of any of these is likely to cause widespread panic – and bats have paid the price. Although they rarely spread these pathogens directly to humans, whole bat colonies are being killed in the name of public health. But where some see a problem, Teeling, a geneticist at University College Dublin in Ireland, sees an opportunity.

The thing is, bats are weird. They don’t just carry headline-grabbing viruses, they are also renowned for the huge number and diversity of pathogens they host. In other mammals these would result in sickness or death, but bats hardly ever succumb to viral diseases. They almost never get cancer, too. In fact, they generally live between three and 10 times longer than other mammals of their size – one male Brandt’s bat tagged in Siberia in 1962 was recaptured 41 years later, still sprightly enough to catch prey and dodge predators. In the past, researchers have put these peculiarities down …