Wednesday, July 27, 2016

Rats #7: Disease vectors throughout history

Since the Great Plague, after which the Black rat (rattus rattus) was ruthlessly hunted and killed off in millions, this species has declined to near non-existence in Europe, though it still thrives in the USA and Africa. The Brown rat (rattus norvegicus) – just as big a disease carrier, didn’t arrive in Europe until the 18th century. 

They are also excellent swimmers and may have entered new regions through self-propelled swimming. The naturalist Pallas reportedly saw great hordes of Brown rats swimming across the Volga river in 1727, from the Asian to the European side, arriving in modern-day Russia. Migrating rats can swim up to half a mile and survive by treading water for three days. Brown rats are more aggressive creatures than their black counterparts and quickly established their superiority all over Europe.
The Volga River, site of a massive rat crossing from Asia to Europe. Image labeled for reuse.
Rats may well like to live in waste dumps and sewers but they are not naturally dirty creatures and are highly intelligent. In many ways it seems that humanity’s war on them is very one sided. Untold millions of rats are ruthlessly exterminated by us, yet the same cannot be said of them where we are concerned. Each time in history that some kind of plague has broken out, rats became the fall guys. During the Byzantine dynasty there occurred the ‘Plague of Justinian’ where up to 10,000 people a week were dying.

The fact is that rats themselves rarely succumb to the disease carried by their fleas. But when they do die, the fleas have to look for other bodies, like humans, to live on, which can happen at epidemic proportions. This happened periodically in history as far back as biblical times, and the flea-born disease is especially scary because the rupturing and decay of blood vessels beneath the skin cause it to gradually turn black, hence the "black death."

Labeled for reuse, by Mikael Häggström
Public domain, via Wikimedia Commons
China experienced Bubonic plague in 1330, from where it was carried west to the Crimea. By 1347 it had reached Europe via seafarers. Before it died down again, from Russia to the Mediterranean Sea 25 million people had died. Some 1,000 villages in England were wiped out by the disease.

The Bubonic plague re-appeared in 1665, when 17,440 people died during the ‘great plague of London,’ and in the 1860’s another outbreak in the Far East led to the deaths of 12,600,000 people all the way across to America. Plague outbreaks weren't limited to early times; Los Angeles had a major outbreak in 1925 and Vietnam saw tens of thousands of cases during the 1960’s. India suffered an outbreak in 1992.

Rats do carry other fatal diseases as well. The Hanta virus, Weil’s disease, Tuberculosis, Listeria and Q fever are all carried by them and easily passed on to humans via household pets. This is one cause for rats being seen as vermin.

In our case, for the most part disease isn't the main cause for concern. It's their constant gnawing and digging that I don't want. And the fact that my very DNA seems to have an aversion to them.

Hats off to where I discovered much of what I know about rats.

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