Trending Science: Rats may not be to blame for the Black Death

Rattus rattus (the domestic rat) has long been blamed for being the vector of plague outbreaks of which killed millions of people across medieval Europe and Asia with some occurring as recently as the 19th century. A break out in the 1340s killed 25 million people in Europe alone. The cause of plague wasn''t discovered until the most recent global outbreak, which started in China in 1855 and didn''t officially end until 1959.

A study just published in the journal ‘Proceedings of the National Academy of Science’ lifts the responsibility for the spread of the disease from rats, pointing the finger at human parasites, such as fleas and body lice, for spreading the bacteria during what is known as the Second Pandemic. This is term given to a series of outbreaks ranging from 1300s to 1800s, including what has been etched into our collective consciousness – the Black Death. Killing a third of the population in Europe, the domestic rat has been in the frame for that catastrophe.

But what if that wasn’t accurate and the creature we have come to associate with the devastation wasn’t actually to blame? The National Geographic quotes the study''s lead author Katharine Dean, a doctoral research fellow at the University of Oslo’s Centre for Ecological and Evolutionary Synthesis. ‘The plague really transformed human history, so it’s really important to understand how it was spreading and why it was spreading so fast.’

The case for the rat''s defence

The team modeled three simulations of outbreaks in the nine European cities for which there is good mortality data. One was based on rats as vectors, another on air-based transmission and the last on fleas and lice living on humans. In seven out of eight models, the human parasitic model mirrored the pattern of the spread most accurately. They maintain the conclusion is very clear, ‘It would be unlikely to spread as fast as it did if it was transmitted by rats. It would have to go through this extra loop of the rats, rather than being spread from person to person,’ the BBC reports Prof Nils Stenseth, based at the University of Oslo.

While the study is mainly of historical interest, an understanding of what happened to trigger one of the most devastating pandemics in human history can help inform how we handle outbreaks of other epidemics. The work done by research such as this could help reduce mortality in the future. Plague is still endemic in some countries of Asia, Africa and the Americas and the World Health Organisation says 3 248 cases were reported world wide from 2010 to 2015, killing 584 people.

So while we might associate the Black Death with medieval images of plague wagons, doctors’ masks and dancing skeletons along with the old villain rattus rattus, the disease is not just locked in the distance past and the rat may well have been blameless!