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Zoonoses: Things Cats Can Spread to Humans

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A zoonosis is a disease of animals that can be spread to and infect humans. This article will focus on the diseases that can move between people and cats. There are far more of these types of diseases than the average cat owner might be aware of, and they can be spread to people in a variety of ways.

How Are Zoonoses Transmitted?

The easiest way to organize and discuss zoonoses is to classify them based on how they are transmitted. The predominant methods of transmission are via:

  1. External parasites
  2. Bites, scratches, and discharge exposure
  3. Fecal-oral transmission
  4. Respiratory and eye (ocular) routes
  5. Urinary tract and birth/abortion

Below, we will discuss the main illnesses that are transmitted from cats to people through each of the above routes. These lists may not be exhaustive, but are meant to highlight the most common diseases.

Zoonoses Transmitted by External Parasites

First of all, let's identify the external parasites that can infest our cats and also don't mind crawling on us.

  • One such creepy crawly culprit is known as scabies or sarcoptic mange of cats. Scabies is caused by Notoedres cati, a mite that burrows into the skin and is highly contagious. Clinical symptoms in the cat include intense pruritus (itching). This leads the cat to do vigorous scratching and there is subsequent inflammation of the skin and secondary infection. Cats can also carry Sarcoptes scabiei, another scabies mite, but it is usually cleared quickly by the cat.
  • Cheylietella blakei, or "walking dandruff" is another skin mite that can infest cats. The most common signs in cats are excessive skin scaling, itching, and redness of the skin. Most humans will accidentally pick up this mite when infested cats are allowed to sleep in bed with them. The most obvious symptom the pet owner notices is frequent bites.
  • Ear mite (Otodectes cynotis) infestation is characterized by dark brown waxy and crusty discharge in the affected animal's ears. This heavy "coffee ground" debris can often lead to a secondary bacterial ear infection because the kitty scratches so aggressively at the ears that the skin is disrupted, allowing infection to invade. Although rare, humans can become infested, though they are not a preferred host.
  • Chiggers, which are larvae of the genera Trombiculidae, and cat fur mites (Lynxacarus radosky—seen in FL, Puerto Rico, and Hawaii) are other skin parasites that can cause skin lesions on cats. Although contagious to humans, infestation is rare. Generally, people will develop a rash characterized by small, discrete, elevated lesions.
  • Last but not least, the most well-known of the skin parasites would be that notorious pest, the flea. Ctenocephalides felis is the most common species of flea that affects cats. These wingless bloodsuckers are quite troublesome. In animals, they can be responsible for anemia, tapeworm infestation, and flea allergy dermatitis. Fleas aren't that picky, and if a cat isn't available, they will bite human beings. In some hypersensitive individuals, this can cause a severe reaction characterized by an almost intolerably intense pruritus. You can learn more here: "Flea Control for Cats."

Bite, Scratch, and Discharge Exposure Zoonoses

Some zoonotic diseases of cats are transmitted by animal bites, scratches, or lesions such as draining, oozing wounds.

  • First of all, let's look at a condition made famous by former rocker Ted Nugent, cat scratch fever. It is called cat scratch disease by health professionals. It is a nasty zoonosis caused by gram-negative bacteria called Bartonella henselae and Bartonella clarridgeiae. Infected cats are more commonly found in warmer climates—fleas transmit the bacteria from cat to cat. The most common way humans get this disease is, just as the name implies, from scratches of cats, most frequently kittens. Flea and cat bites can also lead to injection of the bacterium into people. Contact of cat saliva with open skin wounds may also lead to transmission. Cats usually won't exhibit serious clinical signs of this disease. However, humans exhibit a range of symptoms. These include fever, fatigue, skin eruptions, headaches, conjunctivitis, muscle pain, and enlarged lymph nodes (swollen glands). The disease may also affect the heart, liver, bone, eyes, and spleen in some individuals. In immune compromised people, bacillary angiomatosis is the most frequent resulting condition. While this illness is self-limiting, it may take several months for it to resolve.
  • Tularemia is another zoonotic condition caused by a bacterium called Francisella tularensis. It can be spread to humans by ticks and infected cats. Human symptoms can include high fever, chills, skin ulcers, enlarged lymph nodes, and pneumonia.
  • Feline plague is caused by the bacterium Yersinia pestis. The plague can be transmitted to humans by an infected cat's bites and scratches. Cats usually acquire the plague by eating infected rodents or being bitten by plague-infected fleas. Human symptoms include but are not limited to fever, weakness, dehydration, enlarged lymph nodes, pneumonia and death. You can learn more here: "Bubonic Plague: Cats are Highly Susceptible."
  • Capnocytophaga (formerly Dysgonic fermenter-2) and L-form bacteria are two other bacteria which can be spread by bite or scratch wounds. Immune compromised individuals are at a much increased risk for developing serious illness following infection with these organisms. Death can actually occur within hours of exposure to Capnocytophaga in immunocompromised persons.
  • Sporothrix schenckii is a fungus that lives in soil and decaying organic matter. Cats get infected by the scratches from claws of an infected cat. Sporotrichosis in people is associated with contact exposure with an infected cat, with subsequent contamination of a skin wound. Cases are more commonly seen in workers exposed to a lot of cats such as veterinarians or humane shelter workers. Human infection can turn into local nodules at the area of the skin wound where contamination took place. Infection can also be generalized in the form of enlarged lymph nodes and nodules which can ulcerate and drain. There is also a rare form which affects the bones, joints, nose, mouth, and kidneys.
  • The most significant viral zoonosis is rabies. Yes, Steven King's Cujo made this illness well-known to the masses. Rabies causes fatal acute encephalitis (brain inflammation) in all warm blooded mammals, including humans. Rabies cases in cats continue to increase. The disease is transmitted when the saliva of an infected animal comes into contact with an uninfected animal. This usually occurs through a bite. Clinical symptoms in humans include headache, fever, and discomfort at the site of the bite. This progresses to symptoms of anxiety, confusion, delirium, agitation, and other mental dysfunction. Throat and mouth muscle paralysis leads to trouble swallowing; saliva is not able to be swallowed, thus the sign of "foaming at the mouth". This disease is always fatal in unvaccinated animals and people (only a few reported recoveries ever). Veterinarians and other animal workers at high risk of coming into contact with rabid animals routinely receive the rabies vaccine. Once the disease is underway, there is no effective treatment.

Zoonoses Transmitted Through Contact with Feces

Now let's look at the enteric (digestive system) zoonoses. Humans may acquire these infections when they have contact with their cats or accidental contact with fecal matter.

Some common intestinal parasites of cats produce disease in man. Parents are often especially concerned about their children's health and safety with new kitten purchases, as many kittens have intestinal "worms."

  • The most common zoonotic infection of cats and kittens is roundworm (Toxacara cati) infection. Roundworms may be transmitted to children by their playing in the litter box or by exposure to soil outside that contains infective roundworm eggs. It's also possible for eggs to be on an infected cat's fur. Accidental egg intake my mouth occurs especially with toddler aged children who do not yet understand hygiene measures of hand-washing before eating or putting hands in their mouth. These eggs can survive for months in the soil. This parasite can cause disease in humans due to migrating larvae—visceral (abdomen) larva migrans and ocular (eye) larva migrans are the most commonly seen. The signs of visceral larva migrans include but are not limited to skin rash, fever, coughing, and enlarged liver and spleen. The ocular larva migrans can lead to blindness.
  • Hookworm (Ancyclostoma or Uncinaria) infection is another common parasite of kittens. Transmission of this parasite is by eating parasite eggs or by penetration of the skin by the infective larval stage of the parasite. Children who play in soil contaminated with the eggs are especially at risk. Infection leads to a condition known as cutaneous larva migrans or "creeping eruption." This is a red, intolerably itchy rash of the skin caused by the migration of the hookworm larvae.
  • Strongyloides stercoralis is an intestinal parasite with eggs that are passed in the feces of carrier cats. It can be transmitted to humans by skin penetration and may cause "creeping eruption" or abdominal pain and diarrhea. What makes it unique is that the infection may persist for very long periods of time (i.e. years to a lifetime). If the person becomes immune compromised, serious hyper-infection may result. Infected cats should be isolated and treated.
  • Cryptosporidiumparvum and cryptosporidiumfelis are single-celled parasites that can cause small bowel diarrhea in the cat. Humans may acquire these parasites by accidental ingestion of the oocysts (infective stage) or by drinking contaminated water. The parasites causes small bowel diarrhea in people, too. Consequences are far more severe for immune compromised individuals, and cryptosporidiosis is often fatal in people with AIDS. There is not a highly effective treatment available, though some medications may provide some degree of improvement.
  • Toxoplasmosis (Toxoplasma gondii), another single-celled parasite, can be spread to man by exposure to the infective oocysts that are shed in cat bowel movements. They are generally only shed by the cat for about two weeks after contracting the parasite from eating infected mice. People also become infected by eating raw or undercooked infected meat (pork, goat, lamb), which contains tissue cysts, or by eating unwashed garden vegetables or drinking unpasteurized goat milk. In pregnant women, toxoplasmosis can lead to inflammation of the placenta and an infection in the fetus. For this reason, pregnant women should avoid handling their cat's litter box or if they must clean the box they should wear gloves and a mask and wash their hands afterwards. Some symptoms of the disease in adults are flu-like and include fever, enlarged lymph nodes, malaise, stillbirth, ocular disease, and central nervous system disease.
  • Giardia (also called Giardia lamblia or Giardia intestinalis) is a single-celled parasite that can be spread to humans via contact with feces, and the primary clinical sign is diarrhea. Typically, a gassy, bloated abdomen develops, and bowel movements are malodorous and may contain mucus or blood. The infection may become chronic in stressed or immune compromised people.

There are also several bacteria that infect cats and can cause gastrointestinal symptoms in people. The symptoms can include, but are not limited to, abdominal pain, vomiting, diarrhea, and fever. These bacteria are usually transmitted to humans by accidental exposure to the pet cat's feces. These villains go by the names Salmonella, Campylobacter, E. coli, Yersinia, and Helicobacter.

Eyes and Respiratory System Zoonoses

  • Chlamydiosis is a zoonotic disease caused by Chlamydophila felis. This organism is spread to humans through direct contact with eye discharge from an infected cat. Chlamydophila (formerly named Chlamydia) causes conjunctivitis in humans also.
  • Bordetella bronchiseptica is a bacterium of the feline respiratory tract that can infect humans. People with AIDS or pneumonia are especially susceptible. Direct close contact with a sneezing cat is the major method of transmission. Tracheobronchitis is the predominant clinical symptom. Sneezing, nasal discharge, and pneumonia can also result from infection.
  • Streptococcus A bacteria is one of the organisms responsible for human "strep throat." Close contact with our cats can lead to them sharing the organism with us. The most common clinical signs are tonsillitis and pharyngitis.

Urinary and Birth/Abortion Zoonoses

  • "Q fever" is an illness caused by an agent known as Coxiella burnettii. Humans may contract Q fever when assisting an infected cat during delivery of her kittens or handling aborted fetal materials, from raw milk, or from ticks. Human clinical signs are like the flu and may include fever, headache, malaise, nausea, chills, and muscle aches. Chronic infection can produce inflammation of the liver and heart disease.

Now That You Want to Put Mr. Schnookums up for Adoption

As you can see, there are many potential zoonotic diseases of the cat. Fortunately, thorough routine physical exams and preventive health care (such as vaccines and de-worming treatments) as well as good hygiene practices can greatly decrease your risk of contracting diseases from your beloved pets. So go ahead and hug your cat today. If you have any concerns or want more information on any of these medical conditions, please consult your family veterinarian.

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