The dangers of immunocompromised people and pets (Proceedings)


A large number of immunocompromised persons live with dogs and cats. This situation is not without risks, but pets are part of their life and provide many long-term benefits, offering non-judgmental support, decreasing morbidity and improving survival-time.

A large number of immunocompromised persons live with dogs and cats. This situation is not without risks, but pets are part of their life and provide many long-term benefits, offering non-judgmental support, decreasing morbidity and improving survival-time. Following a few basic rules, can make a daily life safe, healthy and beneficial for both the immunocompromised persons and their pets. Immunocompromised persons with pets should have the same probability to acquire a zoonosis than immunocompromised persons without pets.


Many diarrheal diseases in immunocompromised patients are zoonosis. They are usually acquired from contaminated food, but pets can be a source of infection. The most common agents are:: Salmonella spp, Campylobacter spp, Cryptosporidiumparvum and Giardia spp. General measures that minimize infection by these agents include: wear gloves when dealing with stools, vomiting or other body secretions, adequate hygiene of the litter box, and do not feed the animals raw meet.


Salmonellosis is a common disease in immunosuppressed patients. It has high morbidity and may lead to sepsis. Infection rates in asymptomatic dogs and cats vary from 1 p 3%. Contaminated foods are the most common source of infection in people. Any episode of diarrhea in a pet should be considered as an emergency because the agent is eliminated through the stools. Therapy of an affected dog or cat should only be attempted if there are signs of bacteremia. Antibiotics in absence of bacteremia may prolong the period of transmission. Animals with salmonellosis should be maintained away from the owners during therapy, until 2 negative fecal cultures are obtained. It is important to remember that cold-blooded animals are an important source of Salmonella


Campilobacteriosis can cause intestinal and systemic infection in healthy and immunocompromised persons that can be difficult to eliminate. Sepsis appears to be more common in patients with inadequate immune function. The disease is usually acquired by eating contaminated foods, but up to 42% of young dogs and 35% of young cats do eliminate the organism. Transmission of the organism is more likely in dogs and cats with diarrhea, but asymptomatic animals also can shed Campylobacter through their feces. Fecal smears and culture should be routinely performed in animals with diarrhea. Asymptomatic animals, particularly young ones, should be tested for the presence of Campylobacter. Positive animals should be treated with appropriate antibiotic therapy. Animals should only be reintroduced after 2 negative fecal cultures are obtained.


Almost all cases of Cryptosporidium are in persons with HIV or other immunodeficiencies. Cryptosporidiumparvum is the most important agent in humans and domestic animals. Transmission occurs usually by ingestion of contaminated food and water.


Giardia infections also are usually acquired by ingesting contaminated water or food. However, pets are a potential source of infection and should be tested and treated if positive. Animals should be isolated during treatment e be bathed to remove the oocysts from the skin and hair. Contaminated areas should be disinfected.

Skin disease

Skin infection transmitted by dogs and cats to immunocompromised patients are usually due to Microsporum canis. Occasional infections by Trichophyton mentagrophytes have also been reported. Young cats with M. canis usually have clinical signs, but older cats can be asymptomatic. Topical therapy is usually effective in human beings, but systemic therapy in the pet, and environmental cleaning may be necessary to prevent recurrences.

Other diseases


In patients with AIDS, this protozoan causes encephalitis, forming cysts in the central nervous system.  The primary infection can cause neurological changes, but the majority of clinical cases result from reactivation of an older infection. Cats are the only definitive host of T. gondii harboring the mature stages of the parasite in the gastrointestinal tract and releasing infective oocysts in their feces. Human beings can contract the disease by ingesting the inadequately cooked meat of intermediary hosts or by ingesting oocysts present in feline feces. Since fecal elimination of oocysts is very short, toxoplasmosis is rarely transmitted directly from cats to man. Cats that are seropositive to toxoplasmosis have already stopped eliminating oocysts, presenting practically no risks of transmitting the disease.

To avoid infection, immunosuppressed patients should eat only meats that are properly cooked, maintain good personal hygiene practices, especially after contact with soil, and, if possible, avoid manipulating cat feces. The litter box should be cleaned daily, since oocysts require 2 to 3 days to sporulate. As a result, feces discarded within 24 hours are less infectious. The infection of domestic animals can be prevented by keeping them away from wild animals, and not feeding them raw meat. Most cats do not present clinical signs after being exposed to Toxoplasma, and immunosuppressed are more likely to develop clinical disease and release oocysts during the primary infection. Seropositve cats are safer for the immunosuppressed patients. Cats do not develop a second episode of oocyst elimination, even when infected with the feline leukemia virus.



Dogs and cats are not particularly sensitive to this agent, yet they may develop the disease, becoming a risk for human patients with AIDS. Once the infection by M. tuberculosis or M. bovis is confirmed in dogs, the best option is removal of the animal and adoption by persons with a normal immune system.

Cat scratching disease

Bartonella hanselae and B.clarridgeiae cause cat scratching disease. The main clinical sign is linfadenomegaly. Asymptomatic cats constitute the largest reservoir of these organisms transmitted by arthropods. Human beings can become infected through flea bites, and cat bites or scratches. The bacteria can be found in the environment, and in the fur, nails, and paws of cats. When animals lick themselves, they contaminate their mouths with the bacteria. Bartonella hanselae causes bacteremia immunosuppressed persons causing disseminated lesions. Flea control and avoiding cat bites and scratches are of paramount importance to prevent cat scratching disease. Bites and scratches should be immediately washed thoroughly with warm water and soap. Bacteremic cats should not be treated because elimination of the organism is not always possible and it may favor development of antibiotic resistance.

What to do?

Despite the growth in AIDS cases and the increase in life expectancy for many immunossuppressive diseases, very few veterinarians are prepared to deal with interactions between a pet and an immunosuppressed person. It is important to emphasize measurements that will decrease the risk of acquiring zoonosis.  It is important to advise the owner on how to select a new pet, proper health care.

Chosen a companion

There is always a risk when a new animal is introduced in the environment. Abandoned dogs and cats or shelter animal should be avoided. It is important to choose only health animals, preferably adults. The Centers for Disease Control and Prevention's Healthy Pets, Healthy People website recommends avoiding dogs and cats < 6 months old, as they are more likely to carry zoonotic diseases Young dogs and cats are more likely to have GI pathogens and are more susceptible to dermatophytosis and other infectious diseases. They are also more prone to bite and scratch. Reptiles, amphibians, and exotic animals are not recommended due to a higher risk of salmonellosis and tuberculosis. The new pet should be seen by a veterinarian immediately after being acquired. Cats should be tested for FIV and FeLV. Pets of immunocompromised persons should not be immunocompromised themselves, because it increases the risk of acquiring and transmitting infectious diseases.


Owners should be reminded of the importance of washing hands after manipulating raw food or petting animals. Gloves and masks should be worn when cleaning or coming on contact with stools, urine or vomiting. Ideally, a person with a normal immune system should perform those duties. Gloves should also be worn when giving oral medications or cleaning aquariums. The litterbox should be kept away from the kitchen or places were food is eaten. The litterbox should be cleaned daily and the granulate be disposed appropriately. Masks should be used during the process to avoid inhaling small particles. Once a month is important to disinfect the litterbox with boiling water. This an effective method to kill toxoplasma oocysts.


Many zoonoses are acquired by eating contaminated foods. Dogs and cats should be fed only a high-quality commercial food, and not fed raw meat or eggs. They should not be allowed access to non-potable water, such as surface water or in toilet bowls. Dogs should be confined whenever possible and walked only on a leash to prevent hunting, coprophagia, and garbage eating. Cats also should not be allowed to roam free or to hunt small birds or insects.

Bites and scratches

Rough play should not be encouraged. In case of bites or scratches, the area should be cleaned with water and soap, and the person's doctor should be contacted. Nails should always be clipped small.


Preventive care

Pets from immunocompromised patients should be checked routinely by their veterinarians. All preventive care strategies should be strictly enforced. . Screening of healthy animals to detect fecal shedding of enteric pathogens is of limited value unless serial samples are collected. Erythromycin treatment is indicated in symptomatic dogs or cats with a positive Campylobacter culture, but antibiotic treatment for Salmonella-associated diarrhea is likely to prolong shedding. Any sign of disease in a dog or cat from a immunocompromised owner should be considered a potential emergency. Patients that develop cough, sneezes, vomiting, or diarrhea should seek immediate care. Vaccinations, deworming and heartworm prevention should be done routinely. Cats should be tested for FIV and FeLV. Flea and tick control is also important to prevent introduction of vectors that can carry organisms that may be pathogenic to humans.


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