Would Gerbils Obey the Pied Piper?

Rats are considered an unavoidable bane of urban life and have been generally associated with filth, disease, and pestilence. One of the most ominous events--The Black Death and the following European plague outbreaks--they have been linked to may not actually have involved them (they would blame it on the fleas anyway).

A new study suggests another rodent might have been to blame: the gerbil (actually the great gerbil from Asia). In this study, Schmid and colleagues looked at climatological data contained in tree rings in Europe and Asia (the traditional home of plague) to determine if such conditions were conducive to rat populations. The study attempts to unravel a few paradoxes regarding plague in Europe: what was the rodent reservoir that allowed plague to persist there (which disappeared in the late 19th century when plague outbreaks tapered off) and was plague something that seeded Europe at the time of The Black Death and persisted in rodent populations there? 

What the evidence presented in this paper suggests is that tree ring data in Europe from the time of known plague outbreaks do not support a climate suitable for rat populations to thrive. However, tree ring data from Asia do show a correlation with a climate conducive to gerbil population booms followed by  busts, forcing resident fleas to look for alternate hosts (i.e. humans and other animals, including rats). This finding is at odds with the traditional view that attributes the presence of plague in an infected European rat reservoir.

The authors speculate that repeated introductions of plague to Europe from Asia occurred to produce each plague outbreak--a finding that may absolve the rat of its role in perpetuating Europe's plague outbreaks. 

This study shouldn't dissuade people from having gerbils as pets as it is not applicable to captive gerbils. Similarly, it shouldn't encourage people to have rats as pets (don't forget about rat bite fever). 

What the study does do, at least for me, is provide another great concretization of how infectious diseases affect and are effected by absolutely everything: animal population, international trade, seasons, and, in the case of the Black Death, perhaps the structure of Western society.