Pets and Immunocompromised People

The immune system is made up of several different cells, organs, and chemicals that protect us from invading organisms. Some people have a weak or absent immune system which may be transient, such as those undergoing treatment (for example, chemotherapy) or maturing (premature babies), or permanent, due to disease. This article looks at some diseases people can catch from cats as well as ways to reduce the risk of transmission.

Immunosuppression in people can occur for several reasons, and many medical professionals may recommend rehoming a pet (temporarily or permanently) due to the risks of catching a disease from them. There is no argument that this is possible; however, pets provide many health and psychological benefits to their human owners, and that is especially true for people who have a serious illness. To have to cope with the disease and often invasive and physically tough medical treatment and face the risk of losing a family pet is a lot to ask of a person.

What causes people to become immunocompromised?

There are too many possible causes to list in this article, but some common scenarios may include:

  • Chemotherapy for those undergoing cancer treatment.
  • Cancer itself can weaken the immune system, or cancer treatment (as above).
  • HIV/AIDS while treatments for HIV/AIDS have come along in leaps and bounds, this viral infection which affects the immune system can still make infected patients vulnerable.
  • Organ transplant recipients need to take lifelong immunosuppressive drugs to avoid the body rejecting the don’t tissue.
  • Autoimmune disease.
  • Metabolic diseases such as chronic kidney disease and diabetes.
  • Senior citizens whose immune systems aren’t as strong as those of younger people.
  • People with bone marrow disorders receive chemotherapy followed by a bone marrow transplant.
  • Premature babies whose immune systems haven’t developed yet.


Direct contact:

  • Bites – This may be a play bite or a bite from an aggressive cat or even one who bites when being administering medications or given a bath.
  • Scratches – May happen accidentally, during play or aggression.
  • Licks – This can potentially pass on infection via saliva.
  • Respiratory secretions – Sneezing, coughing.
  • Urine, faeces, vomit – Can all harbour pathogens. Transmission may occur during cleaning or from an accidental spray of urine.

Indirect contact:

  • Fomites – Inanimate objects such as food bowls, floors, bedding, doors etc.
  • Via the bite from a vector such as a mosquito.
  • Ingestion of contaminated food.

What diseases pose a risk?

There are potentially dozens of diseases that are zoonotic (transmissible between animals and humans) which encompass bacterial, viral, fungal and parasitic pathogens. Some of these diseases cause almost no outward signs in immunocompetent people, some can make immunocompromised people very sick, and some can make be extremely dangerous to both immunocompetent and immunocompromised people.


Toxoplasmosis is an infection by the intracellular parasite Toxoplasma gondii, which infects multiple warm-blooded animals; however, the cat is the definitive host to this parasite. Most cats and humans who become infected have mild and self-limiting symptoms (if any), but the disease can be serious in pregnant women, causing abortion or congenital deformities as well as posing a risk to immunocompromised individuals.


Cats become infected when they consume prey or meat containing the infective bradyzoite (an infective cyst) found in the animal’s tissue, or by ingesting infective oocysts which are present in the feces of an infected animal.

People can become infected when they come into contact with infective oocysts when they clean out an infected cat’s litter tray.

It takes 1-5 days for cysts present in the feces to become infective, which shows the importance of twice-daily removal of feces from litter boxes. Cats aren’t the only mode of infection; most people become infected by consuming water or undercooked/unwashed vegetables containing infective oocysts or consuming undercooked meat containing bradyzoites.


Cats and immunocompetent people are generally asymptomatic. Symptoms of toxoplasmosis in immunocompromised people includes localised lymph node tenderness, fever, sore throat, fatigue, general aches, and pains.


Pyrimethamine (Daraprim) and the antibiotic Sulfadiazine.


A bacterial infection that causes enteritis (inflammation of the intestines), Salmonellosis can infect a wide range of animals including humans, cats, and dogs. Salmonella can make even healthy people quite sick. The annual incidence of salmonella in HIV-infected men is 384 per 100,000 compared to 20 per 100,000 in HIV-negative men with pets being responsible for 3% of cases. [1]


Cats become infected by consuming and eating infected prey, eating contaminated meat, coming into contact with saliva or feces from an infected animal or contaminated objects.

People become infected much the same way as cats.


Vomiting, diarrhea, poor appetite, fever, dehydration, abdominal pain, lethargy, weight loss.


Antibiotics, supportive care such as fluids to treat dehydration may also be necessary.


Giardiasis is an infection caused by single-celled protozoa which live in the small intestine of vertebrates and is passed out of the body via the faeces.


Cats and people can become infected with Giardia by ingesting cysts from contaminated feces, the environment (fecal-oral route), fomites (objects such as door handles), eating food washed in contaminated water, eating uncooked food or undercooked food and drinking contaminated water.


In people and cats include foul-smelling diarrhea which is often yellowish in colour and frothy, flatulence, abdominal pain and distension and weight loss.


There are several medications to treat giardia in both humans and cats. Most commonly antibiotics may include Furoxone or Flagyl. Drontal Plus or Panacur can be used to treat giardia in cats.


Cryptosporidium is a parasitic coccidian protozoan that attaches to and replicates in the intestinal epithelium. Non-infective cysts are passed out of the infected animal via the faeces, once in the environment, they mature, becoming infective.


Infection occurs when infective cysts are ingested, which may be via contaminated faeces (handling litter trays, changing nappies of an infected child), the environment, fomites, eating food washed in contaminated water, eating uncooked food or undercooked food and from drinking contaminated water.


Diarrhea, which may have blood and mucus, loss of appetite and weight loss are the characteristic symptoms of cryptosporidium.


There is no cure for cryptosporidium, healthy individuals and cats usually don’t require treatment and will make a full recovery on their own once their immune system has fought off the infection. Drink plenty of fluids to replace those lost in the feces. Anti-retral therapy can be given to boost the immune system.


This fatal viral infection can infect almost all warm-blooded mammals. It affects the central nervous system of those it infects. Skunks and raccoons are a significant source of infection in the United States.


The virus is shed in the saliva and is spread via a bite from an infected animal. The virus affects the brain by causing inflammation, which produces psychosis and aggression. So a usually docile cat will become aggressive once infected.


There are three stages of rabies, prodromal, furious and dumb. Prodromal is the first stage, and symptoms in cats may include low-grade fever, restlessness, loss of appetite. In humans, symptoms include low-grade fever, headache, loss of appetite, vomiting. The next stage, furious brings about signs of aggression, irritability, excitement, incoordination, and convulsions in cats. People may become anxious and agitated. The final stage, dumb causes paralysis, hypersalivation, paralysis and coma in both cats and humans.


There is no curative treatment once symptoms develop in cats and people, and supportive care will be provided. Even cats without symptoms will need to be euthanised. People who have recently been bitten by a rabid animal will be given a fast-acting injection close to the site of the bite; this will be followed up by a series of rabies vaccinations.

Always vaccinate dogs and cats in rabies-affected areas.


A bacterial infection caused by the bacteria Yersinia pestis, the plague comes in three forms. Bubonic, affecting the lymph nodes, septicemic which affects the blood and pneumonic, which affects the lungs. Pneumonic plague is the most fatal form with a 90% mortality rate. The plague (otherwise known as the black death) was responsible for the deaths of 50 million people in the 14th century.


Pneumonic and septicemic are spread via the bite of an infected flea carrying the bacteria. Pneumonic plague is spread via the aerosol droplets of an infected person coughing and sneezing. Cats may also become infected when hunting.


Symptoms of the plague in both cats and humans depend on the type but may include anorexia (loss of appetite), fever, swollen lymph nodes which may become abscessed, coughing and sneezing in cats and people with the pneumonic form of the disease.


Antibiotic therapy is used to treat the plague. Streptomycin and gentamicin are most commonly prescribed. The plague is an extremely serious disease.


Caused by a bacterium that causes enteritis in most warm-blooded animals, including people and cats. A lot of cats can be infected with campylobacter and not have any symptoms. Kittens, cats in shelters and crowded conditions and pregnant cats are all at higher risk of developing symptoms.


The main route of transmission is foodborne, in particular, chicken. Other modes of transmission include raw milk, contaminated water, and fomites. Asymptomatic carriers can pass the bacteria in their feces without any outward signs of infection.


Healthy, adult cats often don’t show any symptoms of infection. Presenting symptoms in both cats and humans include diarrhea, which may contain blood or mucus, abdominal pain, fever, nausea, and vomiting.


In cats and people who are healthy, no treatment may be necessary other than replacing lost fluids. Antibiotics will be prescribed for immunocompromised people.


One of the most common zoonotic infections passed between cats and people, caused by the Pasteurella bacteria which is part of the healthy oral cavity flora of cats. Between 75-80% of cats have the Pasteurella bacteria in their mouths without causing any harm. Cats with tartar and gum disease are particularly at risk of carrying the bacteria.


Cat bites are the most common mode of infection, but you can also acquire the bacteria from cat licks, scratches, and respiratory secretions, for example, if a cat gets close to the face of an immunosuppressed person.


In humans, symptoms include cellulitis or abscess at the site of the bite; localised lymph nodes may also become swollen and painful. Complications in people such as infection of the joints, bones, lungs, and blood may also occur. For cats, symptoms may include abscess, pyothorax, respiratory infection, joint infection, and meningitis.


Generally a course of penicillin, tetracycline, or cephalosporin. If an abscess has formed, your veterinarian or doctor will need to lance it and clean it out.

Cat scratch disease

Caused by a gram-negative bacterium Bartonella henslae. One study has shown that up to 80% of cats have positive antibodies to the disease.


As the name suggests, transmission in humans often occurs via a cat scratch. Dogs, thorns, and splinters may also be reservoirs of the bacteria.


Most cats are asymptomatic to the disease; however, in healthy humans, symptoms may include fever, swollen lymph nodes, muscle soreness, headache, lethargy, and uveitis (inflammation of the uvea of the eye). Immunocompromised individuals can develop more serious symptoms such as severe skin lesions, vomiting, bone lesions, swelling of the brain, liver and spleen involvement, inflammation of the optic nerve and conjunctivitis.


In cats and immunocompetent people treatment isn’t necessary. In immunocompromised patients, antibiotics will be prescribed.


An extremely contagious and common fungal infection that can infect several animals. Ringworm is seen most commonly in kittens and cats in stressful or overcrowded environments.


Cats and humans can become infected by direct contact with an infected animal or person, or indirect contact via spores on bedding, grooming equipment, soft furnishings etc.


Cats typically develop circular patches of broken or lost hair with a scaly redness on the skin. In humans, circular red patches appear on the skin.


Treatment in cats is lime sulfur dips or anti-fungal medications such as Itraconazole or Griseofulvin. Humans can be treated with over the counter anti-fungal creams such as Canesten.


Also known as ‘rabbit fever’, tularemia is a bacterial infection that can be found in the environment. It predominantly lives in the macrophages, a type of white blood cell. The disease can infect dozens of species of mammal and is particularly widespread throughout rabbit and hare populations, hence the name.


Infection can occur from eating animals infected with the bacteria, inhaling the bacteria in contaminated soil, drinking contaminated water or from tick and mosquito bites. Cats can pass the infection on to humans via contact with respiratory secretions, bites, and scratches.


Cats and humans may develop a respiratory infection, skin ulcers, swollen and painful lymph nodes, conjunctivitis, fever, and lethargy.


Antibiotics to treat tularemia in cats and humans. Additional supportive care such as fluids to treat dehydration may also be necessary.

Reducing the chance of infection

Firstly, work with both your doctor and your veterinarian. Let your doctor know you have a pet, and what your routine is. He will be able to give you personalised advice on how to reduce your chances of picking up an infection from your cat. Also, let your veterinarian know because he will be able to work with you to reduce your cat’s chances of developing an infection that can be passed on to you.

Some people’s immune status will change for the better once they have undergone treatment but others may remain immunocompromised for life. So please be aware that this advice is general.

Adopting a new pet: If possible, avoid adopting a pet while you are immunocompromised, but if you must, consider a cat 12 months or older who is in good health.

Desex all cats in the household: Spaying and neutering reduce the incidence of roaming and fighting, both of which can lead to acquiring an infectious disease.

Litter trays: Immunocompromised people should avoid handling litter trays. Have another household member remove urine and feces twice a day and empty and disinfect at least once a week

Feeding guidelines: Avoid raw meat in households with an immunocompromised person.

Food and water bowls: Wash bowls daily in hot, soapy water and use a separate sponge for pet bowls only.

Water: Provide cats with clean drinking water every day. Do not allow cats to drink from toilets, puddles, dams or fish tanks.

Vaccinations: Keep the cat’s vaccinations up to date, killed vaccines are safer.

Parasite control: Treat all pets in the home for fleas and worms, even indoor cats are at risk.

Keep pets indoors: Indoor cats have a lower risk of infection which can be transmitted from outdoor animals (wild or local pets) and reduces the incidence of parasites and diseases from hunting.

Other ways to prevent infection

  • Wash hands frequently, especially after touching animals, before and after handling food, before eating after being in public areas.
  • Clean and disinfect any cat-related bites or scratches and wounds immediately, and seek medical advice. Your doctor may choose to put you on a prophylactic course of antibiotics to be safe.
  • Don’t garden and especially don’t handle soil or potting mix as these contain many pathogens.
  • Keep your cat’s claws trimmed, or apply Soft Paws to the claws which prevent scratching.
  • Avoid touching farm animals or visiting petting zoos.
  • Tell friends and family to stay away if they have an infection, even something as mild as a cold can be life-threatening to an immunocompromised immune system.
  • Avoid changing nappies (diapers) if possible. If you are the sole carer for a child, wash your hands thoroughly after changing nappies.
  • Stay away from chicken coops, areas where birds congregate and don’t clean out bird cages.
  • Be diligent with mould in your home and ensure there is adequate ventilation to discourage growth.
  • Don’t share towels or other personal care items such as hairbrushes and toothbrushes.
  • Cover all scratches and wounds.


1) Celum CL, Chaisson RE, Rutherford GW, Barn-hart JL, Echenberg DF. Incidence of Salmonellosis in patients with AIDS.


  • Julia Wilson, 'Cat World' Founder

    Julia Wilson is the founder of Cat-World, and has researched and written over 1,000 articles about cats. She is a cat expert with over 20 years of experience writing about a wide range of cat topics, with a special interest in cat health, welfare and preventative care. Julia lives in Sydney with her family, four cats and two dogs. Full author bio

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