Matt Ridley

Why have so many of our recent diseases come from bats?

A virus that lives in a fish or a bird is less likely to be able to infect us

I’m no Nostradamus, but 20 years ago when I was commissioned to write a short book about disease in the new millennium, I predicted that if a new pandemic did happen it would be a virus, not a bacterium or animal parasite, and that we would catch it from a wild animal. ‘My money is on bats,’ I wrote. We now know that the natural host and reservoir of the new coronavirus, Covid-19, is a bat, and that the virus probably got into people via a live-animal market in Wuhan.

This is not the first disease bats have given us. Rabies possibly originated in bats. So did, and does, Ebola, outbreaks of which usually trace back to people coming into contact with bat roosts in caves, trees or buildings. Marburg virus, similar to Ebola, first killed people in Germany in 1967 and is now known to be a bat virus. Since 1994 Hendra virus has occasionally jumped from Australian fruit bats into horses and rarely people, with lethal effect. Since 1998 another fruit-bat virus, Nipah, has also infected and killed people mainly in India and Bangladesh. Sars, which originated in China in 2003, is derived from bats, though possibly via civet cats. So is Mers, a similar bat-borne coronavirus that’s killed hundreds of people and camels in the Middle East since 2012.

All these have high mortality but are not easily passed on from one person to another. Covid-19 is the opposite: highly contagious but rarely lethal. There is a good reason for this trade-off between infectivity and virulence, but it helps to think like a virus to understand it. On the whole, unless transmitted by insects, dirty water or sex, new diseases evolve towards lower virulence if they spread far.

‘It’s spreading like royal divorces!’

The 200 or so different rhinoviruses, adenoviruses and coronaviruses that cause what we call ‘the common cold’ have a vested interest in not disabling us much, let alone killing us: they want us to struggle into work, coughing and sneezing, or turn up at parties, kissing and shaking hands.

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Written by
Matt Ridley
Matt Ridley is the author of How Innovation Works: And Why It Flourishes in Freedom (2020), and co-author of Viral: The Search for the Origin of Covid-19 (2021)

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