Creeping through our defences

Epidemic: The Past, Present and Future of Diseases That Made Us by Dr Robert Baker

If you’re a microbiologist, as Robert Baker is, you might well see humanity as a collection of viruses and bacteria. Or maybe not — but he makes an interesting case for his point of view.

“An analysis of human genes reveals that there are large sequences of DNA that unquestionably arose from unexpected sources. It now appears that a very large proportion of our genes arose in other life forms and “infected” us. These are the so-called mobile genetic elements and many are of viral or bacterial origin” — 45%, actually.

“Cell components called mitochondria,” he writes, “are almost certainly purple sulphur bacteria of the sort found in geothermal vents at the floors of the oceans” and found their way into our makeup during an antediluvian epidemic. Eight percent of our DNA consists of human endogenous retroviruses, and he claims that “almost certainly we owe much of our complexity to the fact that we acquired genes from these viruses”.

Epidemics slip through our defences, whether we are created of viruses and bacteria or of the stuff of stars. They have plagued us since time immemorial, in some cases changing the course of history.

The Black Death is irresistible to historians on medical matters; so are a few other scourges, like typhus, which decimated troops during Napoleon’s 1815 retreat from Moscow and the unlucky men in the trenches during the First World War; syphilis, which is still around but generally caught early; and polio, which had been pretty much eradicated before a few clerics and politicians in northern Nigeria, Afghanistan and Pakistan told their followers the drops were poisoned with an anti-fertility drug. The disease is spreading again.

Baker goes into many of these epidemics in depth, giving us case histories, some foul, some fascinating, and some both – such as the doctor who cured a few cases of irritable bowel syndrome with tapeworms.

Here are Baker’s top 10 epidemics: Spanish flu (1918-1920); the Black Death (first noted in the 14th century); malaria; HIV/Aids; cholera; smallpox; polio; typhus; typhoid; tuberculosis.

Now to the new epidemics, most, but not all, because of the human tendency to encroach on to the territories of other creatures. They include the usual suspect, HIV/Aids, but also West Nile fever, the Nipah and Hendra viruses, dengue and avian flu, aka H5N1. if possible.

Bacterial infections sweeping through hospitals in many areas, with strains resistent to antibiotics, also make the list.


Baker notes that soon after Alexander Fleming discovered penicillin “some colonies of bacteria, initially susceptible to the substance produced by penicillium, lost their susceptibility”. That bacteria were able to acquire resistance so rapidly, he writes, “tells us something crucial about the way that such organisms treat our attempts to destroy them. It is with contempt, in fact.”

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