NYC Rats Harbor Fleas That Can Transmit the Plague

Remembrance of Things Pest: Most of the fleas at issue were found upon rats in a single residential building. Matt Frye

A flea that is capable of carrying and transmitting the bubonic plague was found to be living on rats in New York City. Known as the Oriental rat flea, this insect can also serve as a vector (or transmitting agent) for typhus and a bacterial infection called tularemia.

"We have rodents that can serve as a reservoir for the plague, and we have the flea that can transmit it to people, so the only missing component is the pathogen," says Matt Frye, an entomologist at Cornell University, and co-author of a study describing the finding published in the Journal of Medical Entomology.

It's no cause for panic, Frye says, but it does suggest that people might want to be a bit more concerned about the possibility of rats passing diseases to humans.

The study, which is the first since the 1920s to look at parasites living on the bodies of rats in New York, found the animals harbor species including the spiny rat mite, tropical rat mite and the spined rat louse. Oriental rat fleas are the only one of these species known to transmit diseases to humans, though, Frye says.

Researchers collected more than 100 rats from five locations throughout Manhattan. Most of the Oriental rat fleas came from specimens found in a single residential building, in an unspecified area of the city.

This Side of Parasites: Many of the rats were teeming with the fleas. Matt Frye

But many of these rats from this one location were teeming with the fleas. When Frye killed the rats and went to comb the parasites out, "they were pouring off the dead rodent," he says.

"Given its global distribution, I am not surprised that the rat flea (Xenopsylla cheopis) was collected, though it was interesting that it was the only species of flea found," Kaylee Byers, an entomologist at the University of British uninvolved in the study, told The Verge.

A study in October, involving some of the same scientists behind this research, found 18 previously unknown viruses in New York City rats, some of which are very similar genetically to variants known to infect people.