What Diseases Do Mice Carry to Humans?

Mice transmit more than a dozen infectious diseases to people, ranging from viruses that attack the lungs or brain to bacteria that contaminate water and food. The common house mouse, deer mice, and white-footed mice each carry a different mix of pathogens, and transmission can happen through direct contact, contaminated droppings, or indirectly through ticks and fleas that feed on mice first and people second. Some of these illnesses are rare but severe; others are widespread yet underdiagnosed because their early symptoms look like an ordinary flu.

Hantavirus and the Danger of Breathing Dusty Air

Hantaviruses are among the most feared mouse-borne infections in North America. The deer mouse is the primary carrier of Sin Nombre virus, which causes hantavirus pulmonary syndrome, a disease that can progress from fever and muscle aches to life-threatening fluid in the lungs within days. People typically get infected not from a bite but from inhaling tiny particles of dried mouse urine, droppings, or nesting material. Transmission peaks in spring and summer and is more common in and around buildings where mice shelter, because the virus survives longer when shielded from ultraviolet light.¹ Field biologists who handle wild rodents regularly face about a 1-in-1,400 chance of acquiring hantavirus pulmonary syndrome over the course of their careers, which sounds small until you consider that the disease kills roughly a third of those who develop it.²

A related hantavirus, Seoul virus, is carried by brown rats rather than mice, but it circulates on four continents and has been found in pet-rat colonies, making the distinction less tidy than textbooks suggest. Seoul virus causes hemorrhagic fever with kidney involvement, and its case-fatality rate runs about 1 to 2 percent.³ Like other hantaviruses, it spreads through aerosolized rodent excreta, saliva, urine, or feces, and occasionally through direct bites.

Lymphocytic Choriomeningitis Virus

If hantavirus gets the headlines, lymphocytic choriomeningitis virus (LCMV) is the one that quietly flies under the radar. The common house mouse is the principal carrier, shedding the virus in urine, droppings, and saliva. People pick it up when they come into contact with those secretions, whether by cleaning out a garage, handling bedding material, or simply living in a home with an active mouse infestation.⁴ LCMV has a strong preference for nerve tissue, so most symptoms in children and adults are neurological, commonly presenting as aseptic meningitis with headache, stiff neck, and sensitivity to light.

LCMV is considered a neglected zoonotic pathogen, meaning public health systems tend to undercount it.⁵ Most healthy adults recover, but the virus is especially dangerous during pregnancy, when it can cross the placenta and cause severe birth defects or miscarriage. Pet hamsters have also been implicated in outbreaks, because they can contract LCMV from mice in breeding facilities.

Leptospirosis

Mice are efficient spreaders of leptospirosis, a bacterial infection caused by spirochete bacteria of the genus Leptospira. Mice accumulate the bacteria in their kidneys and continuously shed them in urine. The excreted bacteria can survive in water and manure for several weeks, creating an indirect contamination pathway that persists long after the mouse has moved on.⁶ You can get infected through cuts or mucous membranes that come into contact with contaminated water, soil, or food. Direct transmission through bites is possible but far less common than the indirect route through contaminated environments.⁷

Mild cases feel like the flu and resolve on their own. Severe leptospirosis, sometimes called Weil’s disease, can cause kidney failure, liver damage, and internal bleeding. The disease is more common in tropical climates and after flooding, when contaminated water spreads widely, but cases turn up in temperate regions too, especially among people who work around livestock or in sewers.

Rat Bite Fever

Despite its name, rat bite fever does not require an actual bite, and it is not limited to rats. The bacterium Streptobacillus moniliformis lives in the nasopharynx of rodents without making them sick, and people can catch it through bites, scratches, or contact with rodent excreta.⁸ Classic symptoms include fever, shaking chills, and joint pain that can migrate from one joint to another.⁹ In a review of documented human cases, about 83 percent involved a known rat bite or rodent exposure.¹⁰

Rat bite fever responds well to antibiotics when caught early, but without treatment it can lead to endocarditis or abscesses in internal organs. Pet rat owners and laboratory workers face the highest risk. Children bitten by pet rats account for a disproportionate share of cases, often because the bite seems minor and nobody thinks to mention it to a doctor.

Tularemia

Tularemia is caused by Francisella tularensis, a bacterium so infectious that inhaling just a handful of organisms can trigger disease. More than 250 animal species can harbor it, with rodents and rabbits serving as key reservoirs. Ticks and mosquitoes act as vectors, and people can also become infected through handling sick or dead animals, drinking contaminated water, or inhaling contaminated dust.¹¹ Symptoms depend on how the bacteria get in: a skin ulcer and swollen lymph nodes after a tick bite, pneumonia after inhalation, or severe throat infection after drinking bad water. Tularemia is treatable with antibiotics, but it is classified as a potential bioweapon precisely because it is so easy to aerosolize and so potent in small doses.

Murine Typhus

Murine typhus is caused by Rickettsia typhi, a bacterium that lives inside fleas. Rats are the classic reservoir, but the disease also circulates among mice and opossums. Fleas pick up the bacteria when they feed on an infected rodent and then defecate near the bite wound on the next host. When a person scratches a flea bite, the infected flea feces get rubbed into the broken skin or onto mucous membranes.¹² The disease is endemic to seaboard regions worldwide and has been reemerging in parts of the southern United States, particularly Texas and California.¹³ Most people recover with appropriate antibiotic treatment, but severe cases can involve neurological complications, liver inflammation, or kidney failure.

Mice as the Hidden Engine of Lyme Disease

Mice do not transmit Lyme disease directly. Instead, they serve as the primary animal reservoir for the Lyme disease bacterium in the eastern United States, where blacklegged ticks pick up the pathogen by feeding on infected white-footed mice and later pass it to people.¹⁴ Without the white-footed mouse, the cycle of Lyme transmission would look very different. These mice are considered the most relevant natural reservoir for the Lyme disease spirochete.¹⁵

The same white-footed mice also maintain Babesia microti, the parasite that causes human babesiosis, a malaria-like illness that destroys red blood cells. In a study at an intensely zoonotic site, virtually all mice infected ticks with B. microti, even though only about a quarter showed visible parasites in their blood.¹⁶ Because blacklegged ticks feed on mice during their larval stage and on people during their nymphal stage, a single mouse population can seed both Lyme disease and babesiosis into the same community of ticks, and a person bitten by one infected tick can end up co-infected with both pathogens.

Why Acorn Harvests Predict Your Lyme Risk

One of the stranger findings in disease ecology is that oak trees have a measurable influence on how many people get Lyme disease. The connection runs through mouse populations. When oaks produce a bumper crop of acorns in autumn, white-footed mouse populations surge the following summer. More mice mean more hosts for larval ticks, and more infected larvae mean more infected nymphs crawling around the year after that. Research in New York showed that the risk of human exposure to Lyme disease could be predicted from acorn production roughly two years earlier.¹⁷

This is not just a curiosity. A 39-year field study in Maine found that white-footed mouse abundance increased by about 67 percent over four decades, driven by oaks producing more acorns as they grew larger and by warmer spring temperatures boosting acorn crops further.¹⁸ Additional analysis confirmed that acorn production is the stronger driver of mouse numbers, with warmer years adding a secondary boost.¹⁹ As forests mature and the climate warms, the expectation is that mouse populations will keep growing, and with them the burden of tick-borne diseases.

How Transmission Actually Happens in Your Home

Understanding which diseases mice carry matters less than understanding how they get from mouse to human, because that is where prevention lives. The routes fall into a few broad categories:

Airborne particles: Sweeping, vacuuming, or simply disturbing dried mouse droppings and nesting material can aerosolize hantavirus and LCMV. This is the most dangerous route for the most serious mouse-borne viruses, and it is the reason public health agencies recommend wetting down droppings with a bleach solution before cleaning them up.
Contaminated food and water: Mice urinate constantly as they move, leaving traces of Leptospira and Salmonella on counters, in pantries, and near water sources. Any food a mouse has walked across is potentially contaminated.
Bites and scratches: Direct contact transmits rat bite fever and occasionally hantavirus. Pet mice and rats pose a risk here, especially to children who handle them frequently.
Tick and flea intermediaries: Mice do not give you Lyme disease or murine typhus directly. Ticks and fleas feed on infected mice, acquire the pathogen, and pass it along at their next blood meal. Controlling mice around your home reduces the number of infected ticks and fleas in your yard.

The practical upshot is that you do not need to be bitten by a mouse to get sick from one. The most common exposure is passive: breathing contaminated dust, touching a surface a mouse urinated on, or getting bitten by a tick that fed on a mouse months ago. Sealing entry points, storing food in hard containers, and eliminating nesting sites are the most effective ways to cut all of these routes at once.

Mouse Allergens and Asthma

Even when mice are not carrying an infectious pathogen, their presence in a home can make people sick. Mouse urine contains a protein (known as major urinary protein) that becomes airborne as it dries and acts as a potent allergen. A national study of U.S. homes found that in people who were already prone to allergies, elevated levels of this protein nearly doubled the odds of having asthma symptoms in the past year.²⁰ The association did not hold for people without an allergic predisposition, which suggests that mouse allergen does not cause asthma from scratch but can significantly worsen it in susceptible individuals. Mouse allergen exposure is especially high in older urban housing and is a recognized contributor to childhood asthma disparities in cities.

Toxoplasma and the Mouse-Cat Connection

Toxoplasma gondii is a parasite that can only complete its reproductive cycle inside a cat, but it uses mice and rats as intermediate hosts to get there. In rodents, the parasite forms cysts in the brain and alters behavior in ways that appear to make the rodent easier to catch. Early research found that infected rodents lost their innate aversion to the smell of cat urine, a phenomenon researchers called “fatal attraction.”²¹ One influential study reported that this loss of fear was remarkably specific to cat odors, leaving other types of fear and learning intact, and noted that parasite cysts tended to cluster in brain regions associated with fear processing.

More recent work has complicated that tidy story. A 2020 study found that Toxoplasma infection lowered general anxiety in mice, increased exploratory behavior, and reduced aversion to predators broadly, not just to cats. The researchers argued that the behavioral changes stem from widespread brain inflammation rather than a surgically precise manipulation of cat-specific fear circuits.²² For people, the practical concern is that handling mice or their droppings is not the main route of Toxoplasma infection. You are far more likely to encounter it through undercooked meat or by cleaning a cat’s litter box. But the mouse-cat-parasite cycle is a vivid example of how mice participate in disease transmission even when they are not the direct source of human infection.

The Growing Diversity of Rodent Viruses

Surveillance studies using modern genetic sequencing keep finding new viruses in urban rodent populations. A metatranscriptomic survey of rodents in Chinese cities identified 35 distinct viruses from 13 viral families in rectal samples alone, including members of families already known to cause human disease such as coronaviruses, hantaviruses, and hepatitis E-related viruses. Nine of the viral sequences appeared to represent previously unknown viruses.²³ This does not mean those viruses are infecting people. Most rodent viruses never make the jump. But the sheer diversity underscores that mice living near humans carry a much richer microbial world than the handful of well-known pathogens that already have names and diagnostic tests. As urbanization pushes mice and people into closer contact, the opportunity for a new virus to cross the species barrier grows, which is one reason public health agencies invest in rodent surveillance as an early-warning system for emerging infectious diseases.