New York City house mice carry bacteria that can make people sick - including gastrointestinal disease-causing bacteria like C. difficile, E. coli and Salmonella, according to two new studies from the Center for Infection and Immunity (CII) at Columbia University's Mailman School of Public Health.
Researchers emphasized that more study is needed before they could definitively say that serious and antibiotic-resistant infections could be passed from mice to people.
According to the researchers, it is well known that salmonella infections can be the result of food contaminated with animal waste - including mouse feces.
The researchers also published a second study in the same issue that focuses on viruses found in the house mice.
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). Lipkin suspects mice in other major cities carry it, too.
The researchers didn't find any viruses known to infect humans.
But they were concerned mice might actually pose a greater health risk because they live with us in houses and apartments.
Lipkin notes that a lot of antibiotics people flush down the toilet could also travel through the water supply, exposing mice to enough antibiotics for them to become resistant to the bacteria. Most of the mice came from trash compactor rooms in the basements of apartment buildings.
A previous study of rats in NY by investigators at CII found several of the same pathogens, including E. coli, Salmonella, and C. difficile.
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But 37 percent of the mice contained at least one bacterial pathogen, based on the mice's fecal matter or anal swab samples. Past research has found similar bacterial warning signs in mice in other parts of the world, but they haven't led to outbreaks of human disease.
The Centers for Disease Control and Prevention estimate there are approximately 1.2 million cases of salmonella each year in the United States, causing about 23,000 hospitalizations and 450 deaths.
These diseases may spread from mice to humans.
Schaffner said it was worrying that these kinds of antibiotic-resistant bacteria have appeared in animals that aren't treated with drugs.
"We were essentially looking for pathology in the mice and then trying to trace back what was causing the pathology", he said.
Interestingly, Lipkin said, one of the viruses looks like a bug that typically infects pigs.
Lipkin said while they haven't proven mice are responsible for transmitting disease to humans, he recommends exercising caution. For example, there's probably a much better chance you could be exposed to disease-causing microbes in your food or from touching a pet without washing your hands than from rodents. "Then we only had to screen a tiny fraction of the entirety of the sequences that the computer was able to browse through", de la Fuente-Nunez says.
"This is a hard kind of study to do, logistically", Lipkin said.