Introduction
Cats and humans have lived closely together for thousands of years. While this companionship can be rewarding, it also comes with potential health risks. Cats can transmit a number of viral, bacterial, fungal and parasitic infections to humans.
According to the CDC, more than 200 zoonotic diseases can spread from cats to humans (CDC). Some of the most common infections passed between cats and humans include toxoplasmosis, rabies, ringworm, salmonella, cat scratch disease, tapeworm, hookworm and cryptosporidiosis. Many of these diseases produce flu-like symptoms in humans, but some can lead to more serious complications if left untreated.
While the number of transmissible diseases is concerning, there are steps cat owners can take to minimize risks. Following good hygiene practices, controlling parasites, keeping cats indoors, and maintaining annual veterinary visits can all help reduce disease transmission between cats and their human companions.
Toxoplasmosis
Toxoplasmosis is one of the most common and dangerous infections that cats and humans can share. It is caused by the parasite Toxoplasma gondii, which cats and many other mammals can carry. An estimated 11% of the U.S. population has been infected with T. gondii at some point.
The parasite spreads through the feces of infected cats. If a human ingests the parasite by accidentally consuming contaminated food or water or through poor hygiene habits, they can become infected. Toxoplasmosis cannot spread directly between humans.
In humans, toxoplasmosis often causes no symptoms. But it can lead to flu-like symptoms, blurred vision, and in severe cases brain and organ damage. For pregnant women, toxoplasmosis can also cause birth defects and miscarriage.
While toxoplasmosis remains very rare, it is one of the most common and dangerous infections shared between cats and humans due to the severity of symptoms it can potentially cause.
Rabies
Rabies is a nearly always fatal viral disease that mostly affects mammals. It is transmitted through bites and scratches from infected animals, with transmission occurring via infected saliva entering the body through broken skin or mucous membranes. Once symptoms appear, rabies is almost always fatal for cats and humans.[1]
Cats are one of the most common domestic animals to be infected with rabies worldwide. While cases have dropped dramatically in the United States thanks to vaccination, rabid cats still pose a transmission risk to humans through bites and scratches that break the skin. According to the CDC, cats accounted for 303 rabies cases in the United States in 2020.[2] Studies estimate the risk of rabies transmission to humans after a cat bite ranges from 0.01% to 10%, depending on wound location.[3]
Vaccination is key for prevention in cats. Though transmission is rare in areas with good veterinary access, cats should receive the rabies vaccine as kittens followed by periodic boosters in adulthood. For anyone potentially exposed through a cat bite or scratch, immediate medical assessment is vital, as post-exposure treatment with rabies vaccine can prevent the disease if administered promptly.[1]
In summary, rabies is a deadly zoonotic disease present in cat populations worldwide. While human transmission risk is relatively low in vaccinated cats, bites and scratches warrant caution and medical evaluation. Through proactive vaccination and bite prevention, rabies can be effectively managed in cats.
Ringworm
Ringworm is a contagious fungal infection that can be passed between cats and humans.1 It causes a ring-shaped rash on the skin or scalp. Ringworm is highly contagious and can spread through direct contact with an infected animal or surface.
In cats, ringworm causes circular lesions with hair loss on the head, ears, legs, and tail. Kittens are more susceptible. Humans can contract ringworm by touching an infected cat. Transmission occurs when the fungal spores come into contact with broken skin or hair follicles.
On humans, ringworm often presents as a red, circular rash with clearer skin in the center. Itching and inflammation accompany the rash. Without treatment, ringworm can spread across the body. Topical antifungal creams and oral medications can treat ringworm in both cats and humans.
To prevent spreading ringworm, isolate infected cats until lesions heal. Disinfect grooming tools and wash hands after handling pets. Promptly treat ringworm lesions in pets and humans. Ringworm transmission between cats and humans is very common, but manageable with proper treatment and hygiene.
Salmonella
Salmonella is a bacterial infection that can be spread between cats and humans (SVA, 2022). The bacteria is shed in the feces of infected cats, who can remain asymptomatic carriers. Humans can become infected if they come into contact with contaminated feces, litter boxes, or surfaces. Infected humans will commonly experience diarrhea, fever, vomiting, and abdominal cramps (PetMD, 2022). Cats who become ill with salmonella may show symptoms including diarrhea, vomiting, decreased appetite, fever, and lethargy. Preventive measures include proper hand hygiene when cleaning litter boxes and avoiding consumption of raw or undercooked foods that may be contaminated.
Cat Scratch Disease
Cat scratch disease (CSD) is caused by the bacterium Bartonella henselae, which can be spread through scratches, bites, or exposure to fleas from an infected cat. According to a study published in PMC analyzing data from a large national health insurance claims database, the estimated annual incidence of CSD in the United States is approximately 4.7 cases per 100,000 persons under 65 years old (Nelson, 2016). Swelling of the lymph nodes is one of the most common symptoms of cat scratch disease. The bacteria often enter through a break in the skin from a cat scratch or bite, and then multiply inside the lymph nodes causing them to swell as the body fights the infection.
Tapeworm
Tapeworm is an intestinal parasite that cats can get infected with. The most common tapeworm found in cats is called Dipylidium caninum. Humans can become infected by accidentally ingesting an infected flea. According to the CDC, the risk of human infection with this tapeworm is very low, but it is possible (1). For a person to get tapeworms from a cat, they would have to swallow an infected flea, which does not commonly happen. The fleas would need to be ingested whole, as tapeworm eggs are found inside the flea’s digestive tract.
If a human did somehow become infected with tapeworm, symptoms could include mild nausea, diarrhea, abdominal pain, loss of appetite, and weight loss. However, infections in humans are very rare. Tapeworms are easily treated in cats with a dewormer medication prescribed by a veterinarian. It is also recommended to treat all cats in a household and use flea control to prevent reinfection (2). With proper flea prevention and deworming, cat owners have little chance of contracting tapeworms from their pets.
Hookworm
Hookworm is an intestinal parasite that can be passed between cats and humans. The most common species that infect cats are Ancylostoma tubaeforme and Ancylostoma braziliense [1]. These hookworm larvae live in the soil and can burrow into the skin, entering the bloodstream and traveling to the lungs and intestines [2].
For humans, symptoms of a hookworm infection from cats include a skin rash where the larvae entered, as well as coughing, abdominal pain, nausea, and fever as the worms travel through the body. In the intestines, hookworms attach to the lining and feed on blood, which can lead to anemia. Treatment involves medication to kill the adult worms [3]. Preventive measures include avoiding bare feet in areas cats frequent, cleaning litter boxes daily, and having cats tested and dewormed regularly.
[1] https://www.cdc.gov/parasites/zoonotichookworm/gen_info/faqs.html
[2] https://www.petsandparasites.org/cat-owners/hookworms/
[3] https://www.cdc.gov/parasites/zoonotichookworm/index.html
Cryptosporidiosis
Cryptosporidiosis is an intestinal infection caused by the protozoan parasite Cryptosporidium felis. The parasite is spread through the ingestion of food or water contaminated with infected feces. In cats, cryptosporidiosis typically causes diarrhea, which can range from mild to severe. The diarrhea may be intermittent or persistent. Other symptoms include vomiting, loss of appetite, and abdominal pain. Dehydration can occur if the diarrhea is severe. Cryptosporidium infections are highly contagious between cats as the parasite can spread easily through contact with infected feces. Treatment focuses on managing the diarrhea symptoms by providing supportive care such as fluid therapy. Antiprotozoal drugs may help reduce oocyst shedding but do not eliminate the infection. Good hygiene and sanitation are important to prevent spread between cats. While cryptosporidiosis is typically self-limiting in healthy cats, it can be life-threatening in kittens or cats with compromised immune systems. Humans can also become infected through contact with cat feces, so good hand washing is essential.
For more information see: Diagnosis and Treatment of Cryptosporidium and Isospora Infections in Cats and Dogs
Conclusion
In summary, there are several viruses that can be shared between cats and humans, including toxoplasmosis, rabies, ringworm, salmonella, cat scratch disease, tapeworm, hookworm, and cryptosporidiosis. Many of these viruses can be prevented through routine veterinary care, proper handwashing, and careful handling of cats and litter boxes. By staying informed and taking proper precautions, cat owners can greatly reduce the risk of contracting a virus from their feline companions.
To prevent the spread of viruses between cats and humans, it is recommended to wash hands thoroughly with soap and water after handling cats, cleaning up after them, or changing litter boxes. Cats should receive regular veterinary checkups and vaccinations as needed. Any unusual symptoms in a cat, such as coughing or diarrhea, should be evaluated by a vet promptly. Indoor cats are at lower risk for viruses, but owners should still use caution and not allow cats to come into contact with outdoor pets until properly screened by a vet. With some simple precautions, cat owners can continue to safely enjoy the companionship of their pets.
