The Black Death is caused by the gram negative bacterium Yersinia pestis
. This microbe was discovered by Alexandre Yersin of the Pasteur Institute, after an 1894 outbreak of plague in my former home – Hong Kong.
The disease was known long before then but is widely believed to have its origins in Asia.
Conventional thinking is that it spread to Europe via rat vectors, and then European rat population acted as a zoonotic reservoir for the disease that allowed it to persist in Europe for over 400 years.
New evidence now suggests that the rat has been wrongly accused, and actually it is the Asian gerbil that may have been the culprit in causing the plague pandemics, including the 1347-1353 pandemic that wiped out more than one third of Europe’s population.
A study led by Christian Stenseth (who incidentally was one of my co-presenters at World Science Week here in Auckland last year: http://www.royalsociety.org.nz/events/world-science-week-new-zealand/
), used historic climate data to infer that rat populations were unlikely to have expanded during the times of plague, but rather the wet spring and warm summer trend would have been conducive to explosions in Asian gerbil population numbers. The fleas that carry Yersinia pestis
are equally ‘at home’ on a gerbil as a rat, and so the study concludes that it was climate-driven gerbil population booms and subsequent transport along Silk Road trade routes from China to Europe that caused the plague pandemics in Europe.