“New Yorkers are constantly exposed to rats and the pathogens they carry, perhaps more than any other animal,” explains Cadhla Firth, who conducted the study. “Despite this, we know very little about the impact they have on human health.”
In research appearing in the journal mBio, scientists trapped 133 Norway rats at five New York City cites, focusing on rats in residential buildings. In the lab, targeted molecular assays confirmed the presence of 15 bacterial and protozoan pathogens. One virus, Seoul hantavirus, was present in eight rats—the first time the virus has been documented in New York City—with genetic clues suggesting that it may be a recent arrival. Human infection has been associated with multiple cases of hemorrhagic fever with renal syndrome, as well as chronic renal disease in Maryland and Los Angeles.
It is unknown how often humans become sick from rats and what viruses cross over, but according to first author Firth, transmission could happen in any number of ways. Rats leave behind quantities of the pathogens in saliva, urine, or feces that people or their pets come in contact with.
Animal Model for Hepatitis C
Screening methods developed by the Center for Infection and Immunity identified 18 novel viruses, including two rat hepaciviruses dubbed NrHV-1 and NrHV-2. Although these are not the closest relatives to human hepatitis C discovered, their presence in animals commonly used in medical research is noteworthy given limits on animal subjects. The two viruses replicate naturally in the animal’s liver, which suggests that their lifecycle is similar to human hepatitis C virus.
“With the loss of the chimpanzee model for hepatitis C, the availability of an animal model that has fidelity to the human model is extremely important to efforts to develop drugs and vaccines,” says senior author Ian Lipkin, director of the Center for Infection and Immunity. An estimated 3.2 million Americans and 130-150 million people worldwide have a chronic hepatitis C virus infection, which can lead to liver cancer and cirrhosis.
Rats as Sentinels for Human Disease
The study developed out of conversations between Lipkin and the late Joshua Lederberg, a molecular biologist and Nobel laureate. The two scientists wanted to study rats in New York City to have a point of comparison in case a pathogen crossed over and caused a human outbreak.
“Rats are sentinels for human disease,” says Lipkin. “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.”
Lipkin, who has discovered more than 600 viruses over the course of his career, argues in favor of continual monitoring of the rat population along with studies in people to understand how the animals and the microbes they carry make us sick. With modern disease surveillance methods, a repeat of the rat-borne Black Death, which killed as much as 60 percent of the population of 14th century Europe, can remain a dystopic nightmare.
Associate Director, Editorial Communications
Columbia University Mailman School of Public Health
This article originally appeared on the Mailman School of Public Health website.