BETWEEN 1346 and 1353 the Black Death killed over a third of Europe’s population. It took 150 years for the continent to recover. The disease was so devastating that it changed the social order, as a scarcity of labour led to higher wages for the survivors, hastening the demise of feudalism.
The plague was caused by a bacterium, Yersinia pestis, which lives inside fleas. Those fleas, in turn, live mostly on black rats (pictured). It was thus a zoonotic disease: one that is usually carried by animals, but which infects people when given the chance. Since human beings have little evolutionary experience with such diseases, and thus little resistance to them, they can be particularly dangerous. Ebola fever is a zoonosis. So, as their names suggest, are the swine- and bird-flu strains that keep epidemiologists awake at night. Some researchers believe the flu pandemic of 1918, which killed more people than the first world war, also got started in animals.
Trying to work out which animals carry diseases that might infect humans is therefore an important job. It is also a tricky one. There are lots of animal species, a lot of...
from The Economist: Science and technology http://ift.tt/1Abmkw1
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