The “Black Death” is lurking deep down in the subway canals of New York City. 

In the first study of its kind since the 1920s, new research reveals that some rats in NYC are carrying more than 500 specimens of Oriental rat fleas, which are infamous for their part in transmitting the bubonic plague.

“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,” lead study author Matthew Frye, an urban entomologist with Cornell University's New York State Integrated Pest Management (IPM) Program, said in a news release.

Researchers at Columbia University worked with Frye and his colleagues at Cornell to collect more than 6,500 specimens of five well-known species of fleas, lice and mites from 133 rats. They analyzed rats specifically due to the rodent’s ability to act as a vector for human diseases.

They also used molecular screening to look for two other pathogenic bacteria the Oriental rat flea could vector: Rickettsia, which they didn’t find, and multiple species of Bartonella.

"These pathogens can cause a wide range of clinical syndromes, some severe," co-author Cadhla Firth, a research scientist at Columbia University's Center for Infection and Immunity, said in the news release.

Infection occurs when rats’ fleas bite a human, thus introducing their infected blood to the healthy human blood and signaling a bacteria spread.

Study authors said their findings suggest that officials monitor city rats and their fleas, and that people remove food and drink from places where these critters could lurk to try to reduce rodent infestations.

"It's not that these parasites can infest our bodies," Frye said, "but they can feed on us while seeking other rats to infest."

Today in the United States, the plague resides in ground squirrels, prairie dogs and their fleas. The U.S. sees about 10 infections per year, but, according to the World Health Organization (WHO), the disease is more prevalent in other parts of the world. In the past two decades, outbreaks of the plague have occurred in India, Indonesia and Algeria. When diagnosed quickly, the plague can be treated with antibiotics and reduce mortality rates from 60 percent to less than 15 percent, according to the WHO.

According to the Centers for Disease Control and Prevention (CDC), there have been three major plague outbreaks throughout history. The second outbreak, of the “Black Death,” claimed an estimated 60 percent of the European population and wiped out entire towns in the 14th century.

Columbia and Cornell researchers found a host of other viral and bacterial diseases in the 133 rats they studied — some not previously identified and a handful that have the potential to infect humans. Their findings were published Monday in the Journal of Medical Entomology.