Abstract

Nearly every contact with other living organisms, whether it be with humans or other animals, carries some risk of disease transmission. Diseases that are spread from animals to humans are called zoonoses (i.e., zoonotic diseases). Responsible zoos should and do make reasonable attempts to limit the risk of the spread of disease from the animals in their care to their employees and to the general public.^4,9 For the general public, the risk of contracting disease from most zoo animals is minimal to nonexistent due to their distance and isolation form the animals. However, contact areas for the general public can present increased risks that can be controlled with reasonable precautions. For this paper, contact areas refers to those areas in which there is direct physical contact between animals and people. These precautions are most effective when they are part of an overall preventive medicine program for the zoological park.^5,8

Risks of infection from zoonotic disease can be markedly reduced by avoiding direct animal contact. However, this forgoes many valuable educational experiences and the establishment of a direct relationship between animals and the public. A reasonable alternative is adequate hand washing for those in whose direct contact with the animals is touching. Hand washing is perhaps the single most effective personal hygiene procedure for reducing the risk of infection.⁴ Given that fact, all areas should have access to hand washing facilities that are in the immediate vicinity of the contact (or an equivalent, e.g., bacteriocidal hand-wipes).

As outlined by the American Zoo and Aquarium Association (AZA) and the Animal Welfare Act (7 U.S.C. 2131 et. seq.) administered by the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service, animal contact areas should always be supervised by a trained zoo representative. Obviously, animals that are ill, should not be used. Human food consumption should not occur in the immediate area of contact. In addition, zoological institutions should be aware that the Centers for Disease Control and Prevention (CDC) standards advise additional precautions may be necessary for humans who are classified as being at increased risk of disease, including those who are immunocompromised. When a reportable disease is identified, all appropriate local, state, and federal regulatory officials should be contacted.

More detailed information on zoonotic diseases may be obtained from a variety of veterinary and medical textbooks and journals,^1,6 and from public health officials. In addition, the AZA’s Quarantine Protocol provides further testing recommendations.⁷ Also referenced at the end of this report is a review of some of the risks associated with animals and immunocompromised humans.³ Following is a list of disease considerations and control programs recommended for animals commonly used in contact programs. Depending on the disease and history of the animals, testing protocols may vary from an initial or incoming quarantine test, to yearly repetitions. This protocol should be used at the discretion of the institutional veterinarian.

Reptiles and Amphibians

Most notable among the disease risks presented by reptiles is the transmission of Salmonella sp. Salmonellosis is a common and often nonpathogenic infection of reptiles (in one survey, depending on the species, the infection rate ranged from 3–55%).² Diagnosis may be difficult. A cloacal swab or other sample positive on culture for Salmonella sp. is diagnostic for infection. However, due to intermittent fecal shedding of these organisms, false negative cultures frequently occur. So, it is difficult, if not impossible to ascertain with certainty that an animal is Salmonella “negative.” Therefore, all reptiles should be treated as Salmonella carriers. Attempts to eliminate Salmonella carriers with antibiotic therapy have been unsuccessful and may be contraindicated as they can lead to chronic carrier states and increased resistance of these bacteria to antibiotics. Risks of transmission can be reduced in two ways: 1) avoid all direct contact with reptiles or surfaces with which they have come in contact, or, 2) allow only supervised contact followed by hand washing as previously described.

Reptiles can also transmit a variety of other organisms, mostly gastrointestinal in origin, and the same procedures described above should be effective in reducing the risks of transmission to those in contact. These other risks include other gram-negative bacterial infections. Reptiles used in contact areas should be free of snake mites and pentastomids (e.g., Armillifer sp.).

Amphibians may present several of the same zoonotic risks as reptiles, so again, contact should be followed by hand washing.

Birds

Birds used in contact areas should be free of chlamydiosis and zoonotic parasites (e.g., Giardia). Chlamydiosis testing is appropriate for members of the Orders Psittaciformes, Galliformes, and Columbiformes. As in reptiles, salmonellosis can be present and difficult to diagnose and so, birds should be treated as suspects. In the general human population, avian tuberculosis is generally considered to have very low zoonotic potential, however, it can present significant risks for immunocompromised individuals. Care should be taken to avoid public contact with known infected flocks.

Mammals - General

All mammals are considered at risk for infection with rabies. Current rabies vaccines are licensed for use in only six domestic species: dogs, cats, ferrets, sheep, horses, and cows. For wild caught individuals of most species, a prolonged (3–6 months) quarantine is necessary to reduce the risk that they are infected with the virus. Even then, some species, such as skunks, foxes, raccoons, and bats may still represent a greater risk.

Any skin lesions compatible with dermatomycosis (“ringworm”) should be carefully evaluated in order to prevent transmission to those in direct contact with them.

Mammals - Primates

Unless extensive testing has been performed for a variety of viral, parasitic, and bacterial diseases, all direct public contact with primates should be avoided. Public contact also places the primates at considerable risk of contracting diseases from humans.

Mammals - Small Ruminants/Neonatal Ruminants

All small ruminants, (e.g., pygmy goats, sheep, dwarf cattle, llamas, etc.) that are greater than 6-months-old and used in contact areas should be tested for tuberculosis, brucellosis, and leptospirosis. Obviously, any animals with lesions compatible with sarcoptic mange (Sarcoptes scabiei) should be removed from contact. Any animals with lesions compatible with contagious ecthyma (“orf” in man) should be tested and removed from contact until proven negative. Calves should be checked and found free of Cryptosporidium sp. and other infections with protozoa. Other diseases of a potential zoonotic nature include infection with Coxiella burnetii (Q-fever) in endemic areas. Additionally, recent reports indicate that infection with Johne’s disease (Mycobacterium paratuberculosis) may present zoonotic concerns, primarily in goats.

Mammals - Swine

These animals should be checked for gastrointestinal infection with Balantidium sp. efforts made to control this infection. Additionally, consideration should be given to regular vaccination for the bacterial disease, Erysipelothrix rhusiopathiae (“diamond skin disease”).

Mammals - Small Carnivores

In general, due to the potential for bites, small carnivores should be used in contact areas only with extreme caution. Due to the risk of bites, small felids are generally not used in direct contact. If they are, care must be taken that such animals are negative for infection with Toxoplasma gondii. All carnivores should be tested for and be free of zoonotic species of roundworms such as Baylisascaris sp. Small carnivores (e.g., raccoons and skunks) obtained from the wild may present a greater risk of rabies and their use should be avoided in contact areas.

Mammals - Rodents and Lagomorphs

When using rodents and lagomorphs in contact areas, consideration should be given to the risks of bites, past history, and exposure to hantavirus, Salmonella, and tularemia.

Mammals - Chiroptera

At the present time, CDC regulations effectively prohibit the use of bats in direct contact areas.

Fish and Aquatic Tanks

Due to the potential for infection with atypical mycobacteria, Vibrio sp., Erysipelothrix rhusiopathiae, and variety of gram-negative bacteria, contact with fish or touch tanks should also be followed by hand washing.

Summary

It is important to evaluate the risks of zoonotic diseases in a rational context. Contact animals can provide a valuable educational experience for visitors and participants in public programs to zoological parks and aquariums. Most zoonotic diseases of concern in public areas can be prevented with reasonable testing and quarantine programs and proper hand-washing techniques.

These are intended to be general guidelines and the risk of diseases can vary by area, so zoological institution should develop its own zoonoses control program. Two excellent resources for reviewing testing and preventive procedures for many of these diseases are the American Association of Zoo Veterinarian’s Infectious Disease Notebook¹ and the American Veterinary Medical Association’s Zoonoses Updates⁶. In summary, the most effective method for disease prevention is a complete and thorough veterinary program and common-sense sanitary measures.

Literature Cited

1.  Amand W. Infectious disease reviews. In: Proceedings of the American Association of Zoo Veterinarians. Media, PA, USA. 1993.

2.  Cambre RC, Green DE, Smith EE, Montali RJ, Bush M. Salmonellosis and arizonosis in the reptile collection at the National Zoological Park. J Am Vet Med Assoc. 1980;177:800–803.

3.  Greene CF. Pet ownership for immunocompromised people. In: Bonagura JD, ed. Current Vet. Therapy XII. Philadelphia, PA: W.B. Saunders Co.; 1995:271–276.

4.  Heuschele W, Bredeson Heuschele C. Zoonotic disease - reducing the risks. In: Proceedings of the American Association of Zoo Parks and Aquariums. Bethesda, MD, USA. 1988:591–598.

5.  Junge RE. Preventive medicine recommendations. In: Amand W, ed. Infectious disease reviews. In: Proceedings of the American Association of Zoo Veterinarians. Media, PA, USA, Section 1. 1993.

6.  Leveque NW, ed. Zoonosis updates. In: American Veterinarian Medical Association. Schaumburg, IL, USA. 1995.

7.  Miller RE. Quarantine procedures for AZA-accredited zoological parks. In: Proceedings of the American Association of Zoo Veterinarians. Media, PA, USA. 1995:165–172.

8.  Miller RE. Veterinary services in zoos and aquariums. In: Wylie D, ed. Zoo and aquariums fundamentals. In: American Zoo Aquarium Association. Bethesda, MD, USA. 1996.

9.  Shellabarger WC. Zoo personnel health program recommendations. In: Amand W, ed. Infectious disease reviews. In: Proceedings of the American Association of Zoo Veterinarians. Media, PA, USA, Section 7. 1993.