A yearlong assessment of the city's residential mouse population found that what many of these rodents do carry are previously unseen viruses as well as bacteria capable of causing life-threatening human illness. Some of the bacteria were even antibiotic-resistant.
"Mouse droppings may contain harmful bacteria that are difficult to treat with common antibiotics," said Dr. W. Ian Lipkin, senior author of the two papers resulting from the study and a professor of epidemiology at Columbia University's Mailman School of Public Health. "Contaminated areas should be thoroughly cleaned, and contaminated food should be discarded."
Lipkin's research was published Tuesday in mBio, the journal of the American Society for Microbiology.
Over a period of about a year, Lipkin and his colleagues collected 416 mice from residential buildings at seven sites in four of New York City's five boroughs (Staten Island was excluded). Primarily, the scientists caught the mice in or around garbage disposal areas in sub-basements, though five mice were trapped in food preparation/storage areas of a commercial building, and a single mouse was imprisoned in a private apartment.
For one of the two papers
, Lipkin and his team searched for and analyzed bacteria in the droppings of the captured mice. Running genetic tests, the researchers defined 235 separate genera and 149 distinct species of bacteria, including the most common causes of gastrointestinal upset: C. difficile
, E. coli
A leading cause of bacterial food poisoning, Salmonella alone causes 1.2 million reported cases, including 450 deaths, in the US each year.
Further analysis of the identified bacteria showed evidence of genes indicative of antimicrobial resistance to several common antibiotics.
A second paper
concerned the viral load of the mouse droppings.
Here, the researchers discovered 36 separate viruses, including six new ones. None of the viruses identified by the researchers is known to infect humans, however, the genetic sequences matched those known to infect dogs, chickens and pigs. This suggests that some of the viruses might have crossed over from other species.
Though New Yorkers tend to be most squeamish about rats, "mice are more worrisome because they live indoors and are more likely to contaminate our environment," said Lipkin, who is director of the Center for Infection and Immunity at Mailman. "To our knowledge, this is the first such survey in NYC," he said, adding that the laboratory work was "substantial."
Country mice and city mice
Professor John Baines
, an evolutionary biologist working at the Max Planck Institute for Evolutionary Biology in Germany and Kiel University in Germany, appreciates the "multitiered approach" used by Lipkin and his colleagues to look for pathogens within the droppings.
Baines, who was not involved in the research, explained that within some groups of bacteria, there are many different members, some pathogenic (or disease-causing), others harmless. By using different methods of analysis, the researchers were able to learn more about the microbes.
"The more you look, the more you may potentially find," Baines said. "It's a nice combined approach."
The samples studied, gathered only in New York City, are "relatively limited in a geographic context," he said.