Rats may not have caused the Black Death, study suggests

Rats may not have played a critical role in causing the Black Death as is often portrayed, according to a new study.

The Bubonic Plague killed millions in Europe, spreading between 1347 and 1353 with numerous outbreaks ravaging the continent till the 19th century.

The bacterium Yersinia pestis is known to be the causative agent of the plague, with research suggesting fleas carrying the pathogen were spread across the continent by rats during outbreaks.

While the Bubonic Plague begins in wild rodents – the disease’s animal reservoir – it is known to cause outbreaks when it spills over to humans.

However, a new study, published recently in the journal PNAS, suggests that the environmental conditions in Europe at the time would have prevented plague from surviving in persistent, long-term animal reservoirs.

The findings instead suggest these outbreaks that ravaged Europe were likely caused by the plague being reintroduced from Asian reservoirs.

There may have also been “short- or medium-term” temporary reservoirs in Europe, it says.

In the study, scientists, including those from the University of Oslo in Norway, uncovered the environmental factors associated with active rodent-based plague reservoirs in China.

Researchers then compared the findings with active reservoirs of the disease in the western US, and used a modeling approach to determine European plague reservoirs in both modern and historical contexts.

Their analysis suggests that the soil composition and low rodent diversity in Europe at the time may have rendered the continent unfavorable for long-term plague reservoirs.

The study estimates that only about 0.6 per cent of the geographic area of Europe may have had “reservoir-favorable conditions.”

This includes parts of Spain, Portugal, southern France, western/central Italy, and eastern Greece, scientists say.

Scientists say the finding call into question the importance of wildlife rodent species as the primary plague hosts in Europe.

“Our analyses strongly suggest that local environmental factors in Western and Central Europe, including the chemical composition of the soil, altitude, and climates, did not provide favorable conditions for persistent long-term plague reservoirs maintained by wild rodents and their ectoparasites,” researchers wrote.

“We question the importance of wildlife rodents as the main hosts in Europe,” they added.

Instead scientists say Y pestis was likely repeatedly introduced into Europe, and may have survived in local medium-term reservoirs.

“These findings have wide-ranging significance for the study of human plague through history and provide new tools for resolving century-long enigmas posed by plague,” they added.