Abstract

Veterinarians are concerned with preventing the transmission of zoonotic diseases. Special attention to prevention of disease transmission must be paid to those who are immunosuppressed, or those in convalescent centers or schools, particularly if they participate in “hands-on” demonstrations or exhibits at or from zoological parks. This discussion considers diseases potentially transmissible between selected common nontraditional companion animals and immunosuppressed humans.

Introduction

Under the right circumstances, an animal infected with a potential zoonosis may transmit this disease to a human. Physicians and public health authorities must work to minimize the human health risks of zoonotic disease. The veterinarian is increasingly asked not only to screen animals for any and all known zoonotic organisms, but also to counsel those involved in animal programs that have contact with immunosuppressed members of the public. Veterinarians and physicians understand that diagnostic tests for and treatments of potential zoonotic diseases are not 100% effective. Not all potential zoonoses are easily diagnosed. Where organisms are difficult to culture or are shed intermittently (such as Chlamydia, Salmonella, or Campylobacter) repeated testing may be necessary to assure physicians and public health authorities that an animal is under routine disease surveillance. The veterinarian must ensure that the public understands that “negative” is not equivalent to “disease-free,” and that certain precautions, such as proper hand-washing immediately after touching an animal, are essential. It is only through complete disclosure that veterinarians will minimize their liability, and the immunosuppressed person will be able to make the decisions that best balance a psychological need for animal contact with the risks of disease.

Together public health professionals, veterinarians, and physicians can effectively educate the public regarding potential zoonoses. Recognizing the importance of the human-animal bond, it is inappropriate for the human health professional to recommend the elimination of a given animal from the human’s environment without consideration of treatment of disease in the animal as an alternative.^3,9,15 In some species, specific diagnostic testing may be necessary. Some species are inappropriate for contact with immunosuppressed persons due to a lack of adequate diagnostic testing, a lack of disease-eliminating treatments, or a lack of knowledge of carrier states, disease conditions, or “normal” microflora of the animal.

Ideally, animal companions should be screened for the known potential zoonotic diseases they may harbor. If appropriate, therapies should be instituted and complete follow-up diagnostics performed to determine whether the disease agent has been eliminated. With the immunosuppressed person’s permission and knowledge, diagnostic results and recommended treatment plans, including diagnostic or therapeutic follow-up, should be shared with the physician, as necessary. The physician should be encouraged to discuss concerns with the veterinarian. The veterinarian is usually responsible for educating the client in proper sanitation techniques and other safeguards needed during routine animal care. Disinfectants appropriate for home use for “animal clean-up” and recommended by the veterinarian should be made available to the client. A good management program should meet both the physician’s and veterinarian’s criteria for maintaining the health and well-being of both human and animal patients.

Immunosuppressed persons should be provided sufficient zoonotic disease information to allow appropriate contact (if any) with various animals during visits to friends, farms, zoos, etc. The approach should be one of common sense: washing hands well after handling any animal is one example.¹⁴ Educational materials should be available that consider both individual species and their potential diseases, as well as guidelines for safeguarding human health. A copy of this information should probably be supplied to the physician. Open communication between the physician, veterinarian and client should be encouraged.

Discussion

Potential zoonotic diseases of selected nontraditional companion animals are listed below:

Domestic ferret^13,16

With the exception of some of the gastrointestinal nematodes, the infected or infested ferret will usually be clinically symptomatic. Although the risk of rabies is extremely low and there is a rabies vaccine licensed for use in ferrets (Imrab 3, Rhone Poulenc, Athens, GA, USA), some public health authorities do not recognize the vaccine’s efficacy and will require sacrifice and testing of the animal in the event of a bite. Precautions for prevention of disease transmission from ferrets are essentially the same as those recommended for dogs and cats. It is suggested that immunosuppressed persons should not clean litter boxes.¹⁵

Companion domestic rabbit^4,8,9

While wild rabbits may carry Tularemia, Taenia taeniaeformis, and Multiceps serialis, these are more likely a risk to hunters in contact with raw rabbit meat than to pet owners.

Companion small rodents (mice, rats, hamsters, gerbils)^4,8

Guinea pigs^4,8,9

Animals are usually symptomatic; diagnostic and treatment regimens are documented.^4,8,9

Chinchillas⁵

Chinchillas infected with LCM should be euthanatized as there is no specific treatment that will eliminate the virus.

Prairie dog⁶

Risk potential is dependent upon number of generations away from the wild, or contact with wild-caught adults. Accuracy of diagnostics and treatments in these animals has yet to be determined.

African pygmy hedgehogs (Atelerix albiventris)¹

Brushtail possums “Phalangers” (Trichosurus vulpecula)¹²

Efficacy of ante-mortem diagnostic testing and treatment is unknown.

Domestically bred and raised raccoons and skunks may carry Baylisascaris (procyonis and columnaris, respectively). Bacterial and parasitic diseases common to other carnivores may also be carried by raccoons and skunks. Without an approved rabies vaccine, any bite from an individual of either of these species usually results in euthanasia and testing, per public health guidelines. Efficacy of diagnostic tests and disease treatments for these species has not been established.¹⁴

Nonhuman primates (NHPs)^7,8

NHP’s carry the greatest potential for zoonotic disease transmission because of their close genetic relationship to humans.

Birds^2,8

Chlamydia psittaci is the most common of the avian zoonoses; diagnostic tests continue under development. Treatment regimens are considered effective in relieving clinical signs in many species, but true clearance of the organism is debated. Mycobacterium avium usually causes disease in the infected bird; treatment efficacy is debated.

Reptiles^8-10

Invertebrates kept as companion animals or for display and educational purposes include tarantulas, scorpions, hermit crabs, exotic roaches, and others. Little has been documented regarding invertebrate zoonoses.⁹ The author recommends culturing invertebrates fed live prey or insects for Salmonella and other potential bacterial pathogens. Feed colonies (e.g., meal worms, crickets, or mice) should be maintained under hygienic conditions. Uneaten foods should be removed promptly. Water containers need to be sanitized regularly. Gloves and mask should be worn during cleaning of the habitat, as with reptiles. The most frequently noted problem in humans handling tarantulas is skin irritation caused by reaction to the “hair.” An intense pruritus and inflammation may occur on skin surfaces touched by the tarantula. Tarantula bites should be treated as other animal bites and promptly cleaned and disinfected. Scorpion stings should be seen by the physician.

Recommendations and Conclusions

Given the increase in immunosuppression among the general population, an increase in immunosuppressed pet owners and zoo visitors is to be expected. It may be advisable to have information available for participants of contact/visitation programs prior to the visitation. The best way to ensure that immunosuppressed people are not excluded from animal contact by is education of the general public, as well as public health professionals, physicians, and veterinarians. With proper education and communication, keeping of nontraditional pets need not pose zoonotic risks to pet owners. Communication and education between human and veterinary health care providers and the immunosuppressed person is necessary to best prepare immunocompromised individuals for safe contact with nontraditional animals.

No veterinarian can guarantee that an animal is absolutely safe for contact with immunosuppressed persons. The veterinarian can recommend as contact species animals that present minimal risk of zoonotic disease. A physical examination and appropriate diagnostic testing should be performed on animals intended for contact with immunosuppressed persons. For pets, a post-purchase certificate of examination should be provided to the client, with a copy to the client’s physician. The exam record may contain a statement of release from liability with the explanation that negative test results do not guarantee freedom from pathogens, but rather indicate that the animal has been examined for zoonotic diseases, by acceptable diagnostic methods. Examinations should be completed prior to placement of the animal in the client’s home or in known contact with immunosuppressed people.

Animals not recommended as pets or for other contact with immunosuppressed persons include: invertebrates, reptiles, brushtail possums, nonhuman primates, skunks, raccoons, and wild-caught, non-domesticated or exotic species bred for the pet trade. NHP’s probably pose the greatest risk to immunosuppressed humans. The potential for bacterial infection, as well as for serious bite and scratch wounds from NHPs is great. In light of known transmission of retroviruses between macaques and humans, and hepatitis A between chimpanzees and humans, it would be extremely unwise to house an NHP with a human carrying the HIV virus.

Animals recommended, with reservations would include African pygmy hedgehogs, sugar gliders, wallabies, ringtail possums, short-tailed possums, prairie dogs (domestically bred only), and exotic rodents such as duprasi and degus.

Animals the author considers appropriate pet or contact species for immunosuppressed persons include domesticated animals such as cats, dogs, rabbits, ferrets, chinchillas, guinea pigs, rats, mice, hamsters, gerbils, and domestically-bred birds.^3,9,11,15 Domesticated ruminants, equids, and suidaes would also be appropriate as the diseases affecting these species are well-known, as are appropriate precautionary measures. All animals should have routine veterinary care and receive appropriate vaccinations. They should also be adequately socialized to humans and of even temperament. Minimal contact with young animals prior to completion of deworming protocols should be emphasized. Education covering appropriate methods of care, sanitation, and contact (e.g., don’t kiss the animal on the mouth!) is essential.

It is suggested that immunosuppressed persons who attend fairs, livestock shows, rodeos, etc., a masks and eye protection, and that they refrain from handling the animals, equipment, feed, or litter. At a zoo or public aquarium, contact with other humans is probably presents greater risk than does contact with animals, but it should be recommended that immunocompromised persons refrain from participating in hands-on exhibits (petting zoo, tidal pools). Handling of pet store animals should also be discouraged. It is recommended that the patient decline visits to aviaries, animal breeding facilities, and animal processing plants.

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