40. CATS

Your furry feline friend likely brings you joy and companionship in addition to the occasional dead bird or mouse. Sure, your cat might shed on your furniture or spray urine on your belongings to mark them as territory, but you love your pet. Having a cat might even lower your blood pressure and improve your mental health. But although Tiger and Fluffy are good hunters, and you know they are smart, cats may pose some risks to your health.

When it comes to animal bites, dogs get most of the attention. In the United States, approximately 1–2% of all emergency department visits are due to animal bites, and dogs are responsible for 60–90% of these bites. But cats are responsible for 10–15% of the emergency room visits due to animal bites, and 30% of people who visited a doctor for a cat bite have to be hospitalized. There are significant differences in the wounds caused by cat bites and dog bites. Dogs use their teeth and jaws to tear and rip. The resulting gash can be large and open. Cats have sharp teeth that can penetrate deep into tissue and leave pathogens in closed wounds beneath the skin. The mouths of both dogs and cats are teeming with different types of bacteria, but the bacteria that most commonly causes infections after a cat bite is Pasteurella multocida. When P. multocida gets trapped under the skin, it can multiply and spread to surrounding tissue. Such infections look red and swollen and are painful. Left untreated, P. multocida infections can cause cellulitis and septicemia. In rare cases, especially in children, the elderly, and people with suppressed immune systems, these disorders can be lethal.

People who are bitten by a cat should wash their wounds with warm water as soon as possible and control any excessive bleeding. A visit to a health care provider is also in order to ensure that the wound does not get infected. A prescription of antibiotics and a tetanus booster may be recommended, and a decision whether to leave the wound open or closed will be made. The possibility that the cat carries the rabies virus will also be assessed.

Bites are not the only way cats can transmit disease to people. A scratch or simple lick from a cat can spread a bacterium called Bartonella henselae that causes cat-scratch disease (CSD). Approximately 40% of all cats are infected by B. henselae sometime during their lives, but they may not show any signs of illness. Cats get infected with B. henselae when they are bitten by fleas or when flea droppings get into their mouths or under claws. Bacteria are transmitted to people when cats bite, scratch the skin, or lick a person’s wound or scab. Approximately 12,500 people are diagnosed with CSD each year in the United States. People with CSD may develop a fever, headaches, enlarged lymph nodes, and fluid-filled blisters around the wound. On rare occasions, CSD can cause serious illness affecting the brain (encephalopathy), eyes (neuroretinitis), bones (osteomyelitis), lungs (pneumonia), and other organs. The infection often clears up on its own, but sometimes antibiotics are recommended. Eliminating fleas is a good way to reduce the risk of CSD and, as with other animal bites, a scratch should be washed immediately.

Cats also transmit toxoplasmosis, an illness caused by a single-celled parasite called Toxoplasma gondii. The parasite is very common, with approximately 33% of all people on earth having been infected with it. People can become infected with the Toxoplasma parasite if they eat undercooked, contaminated meat or drink contaminated water. Cats sometimes carry the Toxoplasma parasite and excrete it in their feces. People may ingest the parasite accidentally when they clean a cat litter box or touch anything that had contact with cat feces. Most people don’t know they have the Toxoplasma parasite because they have a strong enough immune system to keep it from causing illness. Some people may have flu-like symptoms, swollen glands, and general aches and pains. However, Toxoplasma infections can cause serious health problems, especially in people with compromised immune systems. Concerningly, Toxoplasma can be passed from pregnant mothers to their unborn children. Although most newborns infected with Toxoplasma will not show symptoms at birth, they can develop eye or brain damage later in life.

Toxoplasma gondii may also affect the brain in peculiar ways. Rodents infected with the Toxoplasma parasite become slower and less cautious and display less fear. In fact, they may even be attracted to the smell of cat urine. This change in behavior makes a rat an easy target for cats hunting for a meal. Although the underlying brain mechanisms involved with these new behaviors are not well understood, it appears that neural circuits responsible for fear and anxiety are rewired. Some data suggest that Toxoplasma gondii may have a role in changing human behavior, resulting in psychiatric problems such as schizophrenia, obsessive-compulsive disorder, and bipolar disorder.

Several other diseases can be transmitted from cats to humans, including rabies (a viral infection affecting the nervous system), campylobacter infections (a bacterial skin infection), cryptosporidiosis and giardiasis (parasitic diseases causing gastrointestinal discomfort), echinococcosis (tapeworms), hookworms, roundworms, salmonella poisoning (bacterial infections causing gastrointestinal problems), cat roundworm, and ringworm (fungal skin infection). People, especially women who are pregnant, who have cats should be careful when playing with their felines and gardening in places visited by their pets. Women who are pregnant should not change their cat’s litter box. Children’s sandboxes should be kept covered when they are not in use to prevent cats from using these areas as litter boxes.

There is no need to abandon your cat: feel free to snuggle with your pet, but make sure you wash up afterward to keep yourself healthy.

SUMMARY

Preventability (83)

If you own a cat, maintaining good hygiene practices will prevent most cat-to-human transmission of disease. Of course, you can further limit your exposure to any pathogens hosted by cats if you stay away from cats altogether.

Likelihood (12)

If you own a cat, it is likely that you will be exposed to some of the pathogens hosted by your pet, but these are unlikely to be of major concern.

Consequence (32)

The severity of the illness depends on the pathogen; some cases will cause minor symptoms while others can cause significant health problems.

REFERENCES

Babovic, N., Cayci, C., & Carlsen, B. T. (2014). Cat bite infections of the hand: Assessment of morbidity and predictors of severe infection. Journal Hand Surgery, 39, 286–290.

Bregman, B., & Slavinski, S. (2012). Using emergency department data to conduct dog and animal bite surveillance in New York City, 2003–2006. Public Health Reports, 127, 195–201.

Centers for Disease Control. (2014, April 30). Cat-scratch disease. Retrieved from https://www.cdc.gov/healthypets/diseases/cat-scratch.html

Moncada, P. A., & Montoya, J. G. (2012). Toxoplasmosis in the fetus and newborn: An update on prevalence, diagnosis and treatment. Expert Review of Anti-Infective Therapy, 10, 815–828.

Nelson, C. A., Saha, S., & Mead, P. S. (2016). Cat-scratch disease in the United States, 2005–2013. Emerging Infectious Diseases, 22, 1741–1746.

Sutterland, A. L., Fond, G., Kuin, A., Koeter, M. W. J., Lutter, R., van Gool, T.,. . . de Haan, L. (2015). Beyond the association. Toxoplasma gondii in schizophrenia, bipolar disorder, and addiction: Systematic review and meta-analysis. Acta Psychiatrica Scandinavica, 132, 161–179.