Dirty Rats: NYC Rodents Carry Host of Diseases
Rats treat themselves to takeout in a New York City park, where scientists from Columbia screened the critters for disease.
Credit: Center for Infection and Immunity, Mailman School of Public Health, Columbia University

The rats that dart between trash cans and crawl across subway tracks in New York may harbor some alarming diseases, according to a new study.

Rats in Manhattan are reservoirs for a suite of germs, including E. coli and Salmonella, the research found. Some of the critters were even carrying Seoul hantavirus, which can cause Ebola-like hemorrhagic fever and kidney failure in humans and has never before been documented in New York.

"Rats are sentinels for human disease," W. Ian Lipkin, director of  Columbia University's Center for Infection and Immunity and senior author of the study, said in a statement. "They're all over the city; uptown, downtown, underground. Everywhere they go, they collect microbes and amplify them. And because these animals live close to people, there is ample opportunity for exchange." [10 Deadly Diseases That Hopped Across Species]

The scientists trapped 133 rats from five locations in Manhattan and took DNA samples from the rodents' tissue, feces, urine and saliva. They found 15 of 20 of the bacterial and protozoan pathogens tested for, including E. coli, Salmonella and Clostridium difficile — all of which can cause mild to life-threatening infections in people.

There isn't much data to link rats to outbreaks of foodborne illness. But with about 2.1 million cases of foodborne illness each year in the city, rats in homes and restaurants should probably be considered a risk factor for the transmission of gastrointestinal disease, the authors of the study wrote.

"New Yorkers are constantly exposed to rats and the pathogens they carry, perhaps more than any other animal," Cadhla Firth, who led the study as a research scientist at Columbia's Center for Infection and Immunity, said in a statement. "Despite this, we know very little about the impact they have on human health."

Seoul hantavirus, which is native to Korea and other parts of Asia, was found in samples from eight rats in the study. Humans who are infected with the virus may be asymptomatic, but there have been several cases of hemorrhagic fever with renal syndrome linked to Seoul hantavirus in Maryland and Los Angeles, the researchers note. Genetic clues suggest the disease arrived in New York only recently, which could represent a public-health risk for the city.

The scientists also discovered two rat hepaciviruses, dubbed NrHV-1 and NrHV-2, which are close relatives of human hepatitis C. That could also be good news for researchers developing medical treatments for the 3.2 million Americans who have a chronic hepatitis C virus infection, which can lead to liver cancer and cirrhosis. Rats could be ideal animal models to help develop drugs and vaccines, especially since chimpanzees are no longer used for such research.

The findings were published online today (Oct. 14) in the journal mBio.

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