For the first time in 90 years, researchers have conducted a thorough study measuring the fleas and lice crawling around on the backs of New York City rats. The joint Cornell and Columbia University study, published yesterday in the Journal of Medical Entomology, looked at 133 rats trapped by researchers in Manhattan and found a total of 6,500 fleas, lice and mites, including Oriental rat fleas. These Oriental rat fleas are most troubling because they are infamous for transmitting the bubonic plague, a.k.a. the Black Death, a.k.a.:

The good news is that researchers did not find any plague or typhus bacteria in the fleas they sampled. But come on, we all know it's only a matter of time. "If these rats carry fleas that could transmit the plague to people, then the pathogen itself is the only piece missing from the transmission cycle," says Matthew Frye, the lead author of the study.

According to Science Daily, the plague can still be found in the American Southwest "among ground squirrels, prairie dogs and the fleas they harbor, infecting roughly 10 people each year. In other parts of the world, the incidence of plague is higher." If you're visiting New York City from the southwest, please leave your prairie dogs at home, thank you.

The study also found a big increase in the number of fleas per rat since the last study, conducted way back in 1925. Back then, the calculated Flea Index for New York was 0.22, meaning each rat trapped had on average less than one flea. According to the current study, the Flea Index is 4.1—more than four fleas per rat, on average.

The rats who participated in the study were also found to be carrying a variety of bacteria and viruses, including Bartonella in their fleas, which won't kill you but you don't want it. Our advice is to not go around petting any rats or putting them in your mouth without a rat condom.

The study urges officials to implement Integrated Pest Management programs "that reduce rodent access to food, water, and shelter within human-inhabited structures. Integrated pest management programs often combine exclusion techniques to keep rodents out of structures with population reduction methods." These techniques do not currently include plans for rat-kicking parties.

[Via Wired]