For the severely ill patient, animal companions can offer an important source of pleasure, affection, and even a reason to live. In a study of patients with cardiac disease, pet ownership made a significant difference in survival regardless of the severity of the cardiac disease or the type of pet. For the elderly patients and patients with disabilities, animal-assisted therapy has affected physiological and psychological improvement. Studies indicate the watching fish in an aquarium or petting a dog can lower blood pressure, even among healthy individuals.

Patients with human immunodeficiency viral (HIV) disease must often cope with feelings of isolation and rejection and adjust to increasing physical disabilities. For these individuals, pets can provide continuous, nonjudgmental acceptance and love and a connection to the outside world.

People come to visit, but they can only stay an hour and then they have to go. My cat, she's always there. Bob Pet Owner With AIDS

When you're sick, you don't want to go outside or see anyone. Still, it's okay if your dog crawls up beside you. A dog or a cat doesn't care how terrible you look or anything. It's unconditional love. My heart goes out to these people. I'm just glad I can take care of their animals. Katharine, PAWS volunteer

There are days when I get down in the dumps because of all my friends that have gone. Without my cats, I can tell you, I'd probably be in a mental ward. We just play all day. They're my joy and my happiness. They go beyond the word "companion". Ed Pet Owner With AIDS

Although it is well-known that animal companionship offers benefits to severely ill, isolated, elderly, and disabled patients, the potential risks to HIV-infected individuals are less well understood. People with acquired immune deficiency disease syndrome (AIDS) as well as other patients with severely impaired immune systems are threatened by opportunistic infections. Among these infections are a wide variety of zoonoses: disease that can be acquired from animals or that are shared with animals.

Even though the possibility of exposure and transmission of zoonotic diseases from animals to people cannot be eliminated, it can be minimized. By providing immunocompromised patients with pet care guidelines and appropriate hygiene instructions, physicians can encourage patients to keep their pets and to choose new pets wisely.

Zoonoses

Afraid of infection, I fear the birds (tuberculosis), the cats (toxoplasmosis), my dog, my horse (mycoplasma avium), and people. For weeks I was reluctant to leave the house. I didn't ride my horse for several months. Walking in the park or at the beach was unpleasant because of the birds. My doctors gave contradictory advice - Dr. A said to get rid of all animals. Dr. B said that it didn't matter and enjoy what life I had left. Stephen, Physician With Aids

In the early years of the AIDS epidemic, prudent physicians, unfamiliar with factors involved in the transmission of zoonoses, often chose to err on the side of caution, and advised patients with AIDS to get rid of their pets. Fortunately, this attitude appears to be changing. In a 1989 survey that included 43 health care providers treating HIV-infected patients in community-based settings in San Francisco, 97% of respondents indicated that companion animals were a major source of support and comfort for patients. Seventy-six percent of the survey participants felt that the benefits of pet ownership probably out-weighted zoonotic risks, although only 21% of respondents felt comfortable with their level of knowledge of zoonotic disease.

The incidence of zoonoses transmitted from pets to humans is difficult to estimate. In humans and animals with healthy immune response, these infections are often chronic and subclinical. Mild or asymptomatic cases are frequently undetected or mis-diagnosed. In humans, zoonoses often escape diagnosis due to lack of physician awareness, inadequate diagnostic tests, and vague symptoms. Neither medical nor veterinary school curricula place much emphasis on zoonoses. Of the more than 200 diseases than can be transmitted from animals to humans, some are extremely rare and generally affect only ranchers and meat-processing employees. Other zoonotic pathogens, such as Giardia and Cryptosporidium, are more common and can present a serious public health risk.

Although many zoonoses have been diagnosed in patients with AIDS, an accurate diagnosis does not necessarily indicate the source if the infection. Some zoonoses are species-specific, while others have a wide variety of vectors including pets, stray animals, farm animals, and humans. Many of these diseases can also be acquired from food and environmental sources and may have no relationship to pet ownership. Frequently, zoonotic infections diagnosed in people with AIDS are reactivations of previous infections and have no bearing on current contact with animal companions.

The Risk to HIV-Infected Individuals

Zoonotic diseases reported in patients with AIDS include cat scratch disease, campylobacteriosis, giardiasis, microsporidiosis, Mycobacterium marinum infection, Rhondococcus equi infection, toxoplasmosis, ringworm, psittacosis, pasteurellosis, and salmonellosis. An exhaustive literature search on 278 zoonotic organisms indicates, however, that the incidence of transmission of zoonoses from animals to HIV-infected individuals is extremely low.

Cat scratch disease is the most commonly reported zoonose directly attributed to animal contact. Of 25 reported cases among HIV-infected patients, nearly all involved recent exposure to cats. In comparison, Rhodoccus equi infections have been identified in nine individuals infected with HIV, most of whom were employed as ranch workers or horse trainers. Although 5% if the HIV-infected population develop salmonella infections, most cases are attributed to exposure through food sources. A few salmonella infections, however, have been linked to contact with pet turtles.

Although fecal-oral transmission is the most common means of exposure to Crytosporidium, a wide variety of animals (including humans) are known to transmit this pathogen. Cats infected with the feline leukemia virus may be more likely carriers of Cryptosporidium than uninfected cats .

Prior to the AIDS epidemic, only 10 cases of microsporidiosis were diagnosed since its discovery in the late 19th century. To date, approximately 50 cases have been reported in HIV-infected individuals. A strong correlation between exposure to pets and development of microsporidiosis, however, was reported in only five cases.

Cerebral toxoplasmosis encephalitis occurs in approximately 10% of AIDS patients in the United States and over 25% if AIDS patients in France. Although all species of animals (including humans) can be infected with Toxoplasma gondii, cats are the only animal species to shed oocyst in their feces. Research has shown, however, that most cases of toxoplasmosis encephalitis in AIDS patients are due to reactivation of latent disease. Although caution should be exercised when changing cat litter boxes, people with HIV disease are more likely to be exposed to T. gondii from ingesting undercooked meat or through contact with oocyst-contaminated soil than from contact with litter boxes.

To date, no reported cases of Pheumocrytis carinii, Mycobacterium avium complex or Cryptococcus neofromans among HIV-infected patients can be attributed to transmission from animals.

What to Tell Your Patients

At the earliest opportunity, physicians should ask their immunocompromised patients whether or not they have pets or intend to add pets to their home. By providing intelligent guidance on pet selection, care, and feeding, as well as environmental management, physicians can help patients with HIV disease maximize the benefits of animal companionship while minimizing risk. Although there is still much to be learned about zoonoses, making current information accessible can make a significant difference in reducing potential exposure to opportunistic diseases.