City Rodents Packed With Pathogens

city rodents packed with pathogens

Story at-a-glance -

  • More than 400 New York City mice were trapped over a period of 13 months and 3 to 14 percent were carriers of gastrointestinal disease-causing agents such as shigella, salmonella, E. coli and C. diff.
  • Genes known to mediate antimicrobial resistance to a wide variety of antibiotics were reportedly “widely distributed” in the mice
  • Thirty-six viruses spanning 18 families were also detected in the New York City mice, including at least six “novel” viruses
  • Mice, in particular, may pose an increased risk to humans because they’re known to live inside people’s homes, invading their kitchens and easily contaminating their indoor spaces
  • Experts believe similar pathogens are likely to be found in mice in other urban areas, while country mice may harbor pathogens closer linked to wild animals or possibly livestock, although this is an area that needs further research

By Dr. Mercola

Mice are often viewed as more of a nuisance than a health threat, but mice taking up residence in New York City are teeming with pathogens, including antibiotic-resistant bacteria that could endanger human lives. The finding comes from two recent studies by researchers at Columbia University's Mailman School of Public Health, raising concerns of whether the mice pathogens, including the resistant varieties, could be spreading to humans.

Mice are commonly found living in close proximity to humans, with more than 80 percent of U.S. homes carrying detectable levels of mouse allergens.1 Meanwhile, in urban areas like Philadelphia, Boston and the Big Apple, more than 15 percent of households in such cities report evidence of mice or rats.2 Yet, while it’s known that house mice thrive in areas densely populated with humans, it’s been largely unknown whether they’re silently contributing pathogenic antibiotic-resistant bacteria to the environment.

New York Mice Are Reservoirs of Disease-Causing Microbes

In the first of two studies published in the journal mBio, researchers surveyed mice from seven neighborhoods across New York City,3 including wealthy and low-income areas. More than 400 mice were trapped over a period of 13 months, 3 to 14 percent of which were carriers of gastrointestinal disease-causing agents, including the following:

  • Shigella: This group of bacteria can cause shigellosis, an infectious disease that leads to diarrhea, fever and stomach cramps.
  • Salmonella: Bacteria that can cause salmonellosis infection, which causes diarrhea, fever and abdominal cramps. In severe cases, salmonella can spread from the intestines to the bloodstream and throughout the body, which can be fatal. It’s estimated that salmonella causes 1.2 million illnesses, 23,000 hospitalizations and 450 deaths in the U.S. annually.4
  • Clostridium difficile (C. diff.): C. diff. has become a common reason why hospital patients develop debilitating, recurrent diarrhea that’s hard to resolve, medically. It’s especially rampant among older individuals on antibiotics for other conditions. Mice were found to harbor types of C. diff associated with human disease.
  • Diarrheagenic Escherichia coli (E. coli): While some strains of E. coli are harmless, diarrheagenic E. coli cause watery or bloody diarrhea and abdominal cramps.

Genes known to mediate antimicrobial resistance to fluoroquinolone antibiotics, such as Cipro (ciprofloxacin) and Levaquin (levofloxacin), were reportedly “widely distributed” in the mice, as were genes mediating resistance to beta-lactam antibiotics, which include penicillins, cephalosporins and others.

Further, when the researchers screened kidney samples from the mice, they found genetic evidence of pathogenic leptospira bacteria, which can lead to leptospirosis, a bacterial disease that can cause kidney damage, meningitis, liver failure, respiratory distress and death.

Dr. Dimitri Drekonja, a member of the Infectious Diseases Society of America who was not involved in the study, told HealthDay News, "It's not terribly surprising that house mice would have these bacteria in and on them, when you consider where mice spend their time … And if you did the same analysis of house flies, you'd probably see this, too."5

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Dozens of Viruses, Including Six ‘New’ Viruses, Also Common in House Mice

For the second study, mice were trapped in multiple New York City locations over a one-year period and their feces were tested for viral diversity. Thirty-six viruses spanning 18 families were revealed, including at least six “novel” viruses.6 While none of the viruses were known to infect humans, some of them could cause disease in dogs, chickens and pigs. Whether those viruses could ultimately mutate into strains that could then infect humans is unknown.

“Thus, mice could be serving as little Ubers or Lyfts for viruses between species. And since viruses can mutate, mice could possibly carry viruses that infect humans, if not now, maybe some time in the near future,” Forbes reported.7 The researchers also detected viruses that were not previously associated with house mice and, worth noting, heavier mice seemed to carry a higher number of viruses.

Mice, in particular, may pose an increased risk to humans because they’re known to live inside people’s homes, invading their kitchens and easily contaminating their indoor spaces. "If I had mice in my apartment," said senior researcher Dr. W. Ian Lipkin, director of Columbia University's Center for Infection and Immunity, in New York City, "I'd take it seriously."8

Experts believe similar pathogens are likely to be found in mice in other urban areas, while country mice may harbor pathogens closer linked to wild animals or possibly livestock, although this is an area that needs further research.

As for where the mice may be acquiring antibiotic resistance, this too is unknown, but it’s possible they could be exposed via human waste in sewer systems.9 The researchers of the featured studies next plan to see if there’s any connection between mice exposure and outbreaks of bacterial infections in humans.

Have You Heard of Hantavirus?

In the last 25 years, more than 700 laboratory-confirmed cases of hantavirus have been reported. This group of viruses is carried by the deer mouse, white-footed mouse, cotton rat and rice rat, and can cause a severe, sometimes fatal, respiratory disease called hantavirus pulmonary syndrome (HPS). While symptoms initially begin with fatigue, fever and muscle aches, it progresses to shortness of breath as the lungs fill with fluid. In 38 percent of cases, HPS is fatal.

According to the U.S. Centers for Disease Control and Prevention (CDC), “Recent research results show that many people who became ill with HPS developed the disease after having been in frequent contact with rodents and/or their droppings around a home or a workplace.

On the other hand, many people who became ill reported that they had not seen rodents or rodent droppings at all. Therefore, if you live in an area where the carrier rodents are known to live, try to keep your home, vacation place, workplace or campsite clean.”10

While you may be tempted to sweep or vacuum up mouse droppings, this is not recommended, as it increases the likelihood of stirring up dust carrying the virus particles into the air, where they can be easily inhaled. Instead, any areas with known mice droppings, urine or nesting materials should be sprayed with a mixture of bleach and water, left to sit for five minutes and then disposed of in the garbage.

Antibiotic Resistance Is Known to Spread From Animals to People and Via the Air

While it hasn’t been shown that antibiotic-resistant disease in mice can be transferred to humans, it’s concerning to detect yet another potential reservoir. Further, just as hantavirus is easily transmitted by stirring up infected dust, antibiotic-resistant disease is also known to go airborne.

For instance, research published in Clinical Infectious Diseases revealed that current workers at pig farms are six times more likely to carry multidrug resistant methicillin-resistant staphylococcus aureus (MRSA) than those without exposure to CAFO pigs.11 They also observed active infections caused by livestock-associated Staphylococcus aureus (LA-SA). Worse still, aerosolized MRSA has been detected in the air inside and downwind of a pig CAFO, as well as in animal feed.12

Scientific American also reported, "Recent research shows that segments of DNA conferring drug resistance can jump between different species and strains of bacteria with disturbing ease, an alarming discovery. By simply driving behind chicken transport trucks, scientists collected drug-resistant microbes from the air within their cars."13,14

Further, it’s commonly believed that antibiotic-resistant bacteria spread less easily than regular bacteria and become, in some ways, “less fit.” Research shows, however, that mice infected with antibiotic-resistant strains of Pseudomonas aeruginosa, bacteria that cause lung infections, were more likely to die than those infected with nonresistant strains.15

The resistant bacteria were also better at killing certain immune cells, which suggests they may be more virulent and “fitter” than nonresistant varieties. Similar results were found with two other strains of bacteria, leading the researchers to suggest:16

“A potentially overlooked consequence of the acquisition of antimicrobial resistance could be enhanced fitness and virulence of pathogens … [this] raises a serious concern that drug-resistant strains might be better fit to cause serious, more difficult to treat infections, beyond just the issues raised by the complexity of antibiotic treatment.”

How to Keep Mice Out of Your Home

It’s possible to have rodents in your home even if you’ve never seen one. If you’ve spotted droppings or heard scurrying in your walls, these are common signs of rodents. To keep mice from taking up residence in your home, first seal up holes on both the inside and outside of your home to keep mice out.

“Fill small holes with steel wool. Put caulk around the steel wool to keep it in place. Use lath screen or lath metal, cement, hardware cloth, or metal sheeting to fix large holes. These materials can be found at your local hardware store,” the CDC notes.17

If you know mice are in your home, traps can be used, including live traps that allow you to release mice outdoors, a good distance from your home, but if you’re looking for a more comprehensive solution you should also make your home and surroundings less hospitable to mice by:

Cleaning your yard: Remove overgrown landscaping and junk piles in your yard. By doing so, mice may be less tempted to live near your home and are less likely to enter your home. Areas you may need to address include:

  • Compost, wood, rock and scrap piles
  • Overgrown grass or weeds
  • Overgrown shrubs
  • Pile of leaves
  • Fallen trees and messy sheds

Decluttering your home: Mice may be tempted to live in ideal nesting spots such as messy basements, garages, attics and closets. Declutter these areas and other locations so mice aren't tempted to reside in them.

Clean up crumbs or food debris on surfaces and floors: When cooking, clean dirty dishes immediately instead of letting them sit out.

Store food in places unreachable to mice, such as the refrigerator or inside containers made of glass or very sturdy plastic, which they can't nibble through. If you have pets, only serve the amount of food the animal can finish in one sitting, so mice aren't tempted to eat their leftovers.

Block doorways or pathways that mice can enter in: These animals may enter your home through the same entrances you do. Ideally, add a door sweep or barrier to exterior doors to help keep mice away.

Pay attention to holes or cracks: If you see a mouse, pay attention to where it runs and look for possible entryways where they can pass through. Try sticking a pencil in the hole. If the pencil can fit, it's likely that a mouse can go inside the hole.

Seal unconventional entry points: Close up holes you can see, and don't forget about holes you have drilled. Holes around pipes or wiring tend to be overlooked, but these can act as a mouse "superhighway" system. Inspect vents and drains in your home and ensure they're covered with fine mesh screen. These include soffit/attic vents, ridge vents, HVAC drains/vents, dryer vents, gas vents and kitchen and bathroom exhaust vents.

Use peppermint essential oil as a mice repellent: The smell of peppermint can be overwhelming and offensive to mice. Try adding a few drops of peppermint oil to your cleansers or dab some of the oil onto cotton balls and tuck these into corners of pantry shelves to get rid of mice naturally.

Use cloves or clove essential oil as a mice repellent: Rats find the smell of cloves distasteful and overwhelming. Place 20 to 30 drops of clove essential oil onto cotton balls and place them strategically around your home. If you're using whole cloves, wrap these in an old piece of cotton shirt and use in place of cotton balls. Just make sure you don't have pets wandering around that can ingest the cotton balls or clove.

Plant vegetation that small birds and animals can enjoy, and avoid leaving out store-bought foods: If you like leaving food out in your backyard for birds and other wildlife to feed on, plant vegetation instead and don't place store-bought foods outside.

Mice and other animals are attracted to seeds and store-bought foods, especially when these are left out in your yard at night. In the long run, this may cause a mice infestation.

How to Safely Clean Up After Mice

To minimize your risk of picking up an infectious disease from mice in your home, as mentioned do not sweep up or vacuum droppings. Areas contaminated with mice droppings, urine or nesting should be sprayed with a mixture of 1 part bleach to 10 parts water, then allowed to sit for five minutes. The area can then be cleaned up with a paper towel and disposed of in the garbage (where rubber gloves while cleaning up after any suspected mice).

Lastly, the CDC recommends disinfecting the entire area with the bleach solution, mopping floors, cleaning countertops and steam cleaning or shampooing upholstered furniture and carpets if necessary. Clothing and bedding should be washed in hot water.18 Finally, while it’s easy to panic at the thought of disease-causing mice roaming over your kitchen counters, it’s also important to keep things in perspective. As Drekonja, the infectious disease specialist, told HealthDay:19

“We live in a world of microbes, many of which are beneficial. Some, of course, are not, and people can be exposed to them in numerous ways. House mice would be just one potential route of many. That's why we should all wash our hands regularly.”