Those poor, misjudged rats? According to infectious disease experts in Norway and Italy, rats aren't to blame for the spread of the Black Death, which has previously been referred to as the species' most infamous crime. In fact, humans might've been directly involved, reports the CBC. While studying nine European plague outbreaks that killed 125,000 people between 1348 and 1813—considered the second pandemic of the bubonic plague, following the first in the sixth century—researchers at the University of Oslo and University of Ferrara used mathematical models to compare scenarios of transmission by humans, by fleas carried by rats, and by parasites carried by humans, reports CNN. In seven of nine European cities, the latter scenario best matched evidence in mortality records.
The theory is that fleas and lice carried by humans would bite an infected person, then jump to another victim and bite again, quickly spreading the disease, per the Independent. Researchers believe this is what led to the deaths of 10,000 people in Florence in 1400, 17,000 people in London in 1563-64, and more than 53,000 people in Moscow in 1771, according to the study published Monday in PNAS. Experts believe this may also explain more recent plague outbreaks in Africa. But perhaps you shouldn't feel so bad for those misjudged rats after all. The study notes the flea-carrying rodents did help spread the plague in the third pandemic, starting in 1855. There are also researchers who continue to believe rats were involved in the Black Death, reports National Geographic, suggesting this "provocative" study won't be the final word. (The Black Death had an upside.)