17 Nov 2014

As we focus on Ebola, we underestimate bird flu at our peril

Word of the week: zoonosis. Why am I standing outside an unlucky duck farm in Yorkshire?

Three weeks ago I stood instead outside an Ebola treatment centre in Sierra Leone from which, statistically speaking, only four of the 12 people inside were likely to emerge alive.

Does the risk of a not particularly deadly to humans strain of bird flu really deserve headlines while the humanitarian tragedy of Ebola continues?

Well no. But also yes, because bird flu and Ebola share one very important thing in common. Something which, on our overcrowded and hungry planet, we ignore at our peril.

Both are animal viruses with a proven ability to jump into humans and kill them with ease. They are what scientists call zoonoses.

The exact strain of bird flu at the heart of the Yorkshire outbreak is as yet unknown and most probably of very low risk to humans. But it is related to infamous strains like H5N1 and therefore deserves our attention.

The H5N1 virus can be exquisitely deadly. It kills approximately 60 per cent of those it infects. It’s important to mention that it is very hard to catch — requiring direct contact with poultry — and since 2003 it has not killed more than 400 people.

But those facts bear a striking similarity to what journalists like me used to say about Ebola. It too is quite difficult to catch, outbreaks were rare, but deadly.

And that’s the thing about zoonoses. Animal viruses haven’t evolved to live in a human host, but a quirk of evolution has given a few of them the ability to infect us. They’re usually hard to get, but once infected, it can be bad news indeed. Some of most deadly infections we know are zoonoses: Rabies, Ebola, SARS and bird flu.

Take Ebola and bird flu. Because of their lack of experience of living with a human host, they haven’t evolved any manners. Both replicate in such a way that they leave the average human’s immune system overwhelmed — accounting for the high mortality.

This is why experts in infectious diseases have been warning of the threat of zoonoses for years. They can be the most deadly forms of infection because the viruses involved don’t know how to behave in humans — and our immune system has no experience of them.

The reason of the alarm is that our demands as a species are increasing the chance of animal viruses jumping into humans. Such “zoonotic events” may be becoming more common, and more dangerous.

Don’t believe me? Look at Ebola. It’s an animal virus (of as-yet-unknown origin) which has made regular forays out of the jungle and into people since it was first identified in 1976. Most outbreaks were linked to bushmeat consumption and or logging/forest clearing activities in central Africa.

Everyone quite justifiably expected Ebola to stay right where it was. Bumbling around the jungle in some animal, making rare and not very widespread forays into humans. How wrong recent events have proven us to be.

Population pressure on the jungles of southern Guinea where the outbreak started are extreme. New roads and mobile phones mean people can gather and disperse at alarming rates. Ebola did what no-none expected. It moved from the jungle to the city and spread.

As I’ve said, the outbreak of bird flu in Yorkshire is not a threat to humans in itself. But it serves to remind us that bird flu viruses, which can also jump the species barrier with deadly effect, take advantage of highly intensive, highly interconnected poultry farming on which our diets now depend.

They’ve been on our radar for more than a decade without causing the pandemic many warned of, and that’s encouraging. But it doesn’t mean they can be ignored.

Follow @tomclarkec4 on Twitter.

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