Rats already have a bad rap. Their large size, scurrying movements and propensity for scavenging garbage make them one of the most unpopular city-dwellers. Now we have another reason to stay away from these furry foes.

New York City rats are apparently carrying tons of pathogens, some of which cause food-borne illnesses, a new study published in the journal mBio found. Even scarier, the researchers found "novel viruses" on the rats in their sample.

"Our findings indicate that urban rats are reservoirs for a vast diversity of microbes that may affect human health and indicate a need for increased surveillance and awareness of the disease risks associated with urban rodent infestation," the study says.

A team of researchers at Columbia University examined 133 rats they caught by setting traps in four buildings and a park in Manhattan. The scientists took samples of blood, urine, feces and tissues from a number of organs from the rats and extracted DNA from those samples to analyze the gene fragments. This is the first time anyone has used DNA to trace pathogens in any animal species in New York City.

The results aren't pretty. The researchers found that 40 percent of the rats had at least one viral infection, with 13 rodents infected with more than five viruses, and nearly all of them had a bacterial infection. The scientists found pathogens such as Salmonella and E. coli. They also found Seoul hantavirus and Leptospira, two pathogens that cause fevers. In short, you should probably not cuddle with any of the rats you see on New York City streets.

One of the most important discoveries of the study could be that the researchers found two new species of viruses similar to the virus that causes hepatitis C, a liver disease. This is significant because it may help scientists develop a way of combating hepatitis C, which affects 130 to 150 million people around the world.

The scientists also found 16 other unknown species related to viruses already causing diseases in humans. The study suggests that as humans and rodents continue to be neighbors, there's an increasing chance of passing along disease. 

While New York is famous for its rats, a recent survey released by pest control company Orkin found that New York is actually just the fourth rattiest city in the U.S. The top honor goes to Chicago. That means scientists should probably see what diseases rats in the Windy City are carrying, too.