Cats and Mice - a Deadly Combination

What Else Did my Cat Bring Home?

Photo of Cat Playing with Dead Mouse
Cat With Dead Mouse. © Getty Images / Stefan Wackerhagen

Cats love to chase (and sometimes kill) mice. That's a given, and something that most people do not find too alarming. In fact, people in many countries still utilize "barn cats" to dispatch unwanted rodents - a win-win situation for all parties (except the rodents). The cats have plenty of food available, and the farmer is assured of grain bins undisturbed by hungry mice. A perfect scenario, eh?


In addition to barn cats, many suburban indoor-outdoor kitties will occasionally bring home a small kill to proudly display, which we humans (depending on our constitutions) might or might not allow him to eat. If not, we might be tempted to just pick it up by the tail and dispose of it in the trash container, or down the toilet. The problem is that, depending on the region, those little mice may be loaded with a variety of "nasties," that neither you nor your cats want to encounter. Romeo, the cat pictured on page two, was infected with toxoplasmosis twice, after catching and eating mice. The toxoplasmosis led to uvitis, which in turn led to glaucoma. Romeo is now an indoors-only cat as a result of this chain of events. Although most cats are exposed to toxoplasmosis at one time or another, the usual reaction is mild. However, Romeo's experience underscores the potential deadliness of this organism.

Another case in point:

The Dreaded Hantavirus

In May of 1993, a new hantavirus, Hantavirus Pulmonary Syndrome (HPS) was identified in New Mexico, after forty-two people were infected, with eleven fatalities. Since that time, the new strain has been discovered in other parts of the U.S., with various rodents, including the common house mouse (Mus musculus) acting as hosts, and the incidence of disease in humans has become widespread.

Several other hantaviruses that affect humans exist worldwide, and have been found responsible for outbreaks of hantavirus among animal caretakers and laboratory workers in Korea, China, Japan, Scandinavia, the U.K., France, the Netherlands, Belgium, and the former Soviet Union.1

Although HPS can be transmitted to humans by handling infected mice, inhalence of the aerosols produced directly from the saliva or excreta of the animal is the most virulent means of transfer, if not the most common. For these reasons, it is wise to wear not only rubber gloves when handling a mouse your brave hunter brings in, but also a mask, and to thoroughly scrub any surface area the mouse may contacted with a disinfectant.

Symptoms of HPS in Humans

Early symptoms of HPS are very similar to those of other respiratory illnesses, including pneumonia, and may consist of:

  • Headache
  • Gastrointestinal complaints
  • Fever
  • Myalgia (muscle pain)
  • Variable respiratory symptoms

The condition can quickly progress into acute respiratory distress and pulmonary edema. Since the incubation period for HPS is from one to three weeks, early symptoms of this nature should be reported to your physician if you have had contact with a rodent during that time frame.

The Center for Disease Control (CDC) is investigating whether other animals that prey on rodents may be carriers. The UCSB Office of Research said, "The impetus for this research is a 1987 study suggesting that cats, which tested positive for two other hantaviruses-the Hantaan and Seoul types-may help transmit the virus to humans in China." However, the CDC has stated unequivocally that cats are not carriers of the hantaviruses that cause HPS in the United States, nor can it be transferred from one person to another. Although results are inconclusive as yet, virologists also think most non rodent carriers are "dead-end" hosts, which means they are unlikely to infect people. Unfortunately, cats do not get off quite as easily with the next zoonose we'll discuss.

1 Institutional Animal Care and Use Committee

Next > Toxoplasmosis: not just for pregnant people

Toxoplasmosis has long been dreaded among pregnant women who live with cats. True, cats become carriers of the parasite ( Toxoplasma gondii ) from hunting and catching mice. The virus is shed in the cats' excrement, and pregnant women can contract it from handling litter box duties, and pass it on to the unborn baby with potential for birth defects and/or death of the foetus. Healthy adults very seldom are even aware that they have been exposed to toxoplasmosis, however immunocompromised people (HIV or transplant patients) are at risk.

However, if another household member will volunteer to keep the litter box clean, there is no need to throw out the cat in any of these situations.

Other sources of toxoplasmosis are eating undercooked meat and handling garden dirt that may contain the parasite. Therefore, pregnant women and others at risk, should always wear gloves when gardening, and make it a habit to cook meat thoroughly.

Other Zoonotic Diseases Implicating Mice

Hantavirus and toxoplasmosis are the better-known zoonoses we can get from mice. Here are a few others which are rarer and probably not as wide-spread as the former two.

Yersinia Pestis The Plague, Black Death
Yes, this is more or less the same disease that wiped out twenty-five percent of the world's population from the 14th through the 17th centuries. The disease is transmitted to humans by:

  • Contact with infected rodent fleas or rodents. Fleas may remain infected for months. Note: a protein secreted by the Yersinia is a coagulase that causes blood ingested by the flea to clot in the proventriculus. The bacillus proliferates in the proventriculus, and thousands of organisms are regurgitated by obstructed fleas and inoculated intradermally into the skin. This coagulase is inactive at high temperatures and is thought to explain the cessation of plague transmission during very hot weather. Pulmonary form spread by airborne or droplet infection. Human infections from non-rodent species usually result from direct contact with infected tissues, by scratch or bite injuries, and handling of infected animals. Several recent reports have detailed human plague associated with exposure to domestic cats. Exposure can be from inhalation of respiratory secretions of cats with pneumonic plague or by contaminating mucous membranes or skin wounds with secretins or exudates.
    UC Santa Barbara Zoonotic Diseases Study


    By far, the most prevalent cause of salmonella in humans is by eating improperly prepared foods. However, it is thought that the house mouse may also be a host of the infection and may play a role in human and animal salmonellosis. Eight worldwide studies indicated a wide range of cats tested were culture-positive for Salmonella.



    Found most often on the East Coast of the U.S. in rodent-infested housing, and is transmitted by a mite carried by the common house mouse. The disease causes ulceration of the area surrounding the mite bite, fever, and a rash over the body and limbs. Rickettsialpox is treated with Tetracycline. The obvious conclusion is that, cute as they might be on T.V. and in the movies, mice are not our friends, nor are they particularly suitable for cat food. Besides the obvious dangers of cats living in large colonies (FIV, FIP, and FeLV), perhaps barn cats' steady diet of mice and other rodents contributes to their relatively short life span.

    As for our surburbanite kitties, whether indoor-outdoor or indoor only, they would be better off without the addition of mice to their diets. If you feel compelled to let your cat have an occasional snack on mice, they are available online for sale and shipped frozen, usually in lots of 25 or 50. Sort of "mousesicles," if you will. Personally, I'll pass on that idea, and I didn't even allow my cats a vote.