Preventive Medicine for Zoo Animals
The foundation of a medical program for zoo animals is preventive medicine. Preventive medical programs should be adaptive and include attention to individual specimens as well as the herd, troop, or flock. Components of the program include quarantine of new arrivals, periodic fecal examinations and treatments for parasites, booster vaccinations, health screening procedures, nutrition evaluation, necropsy examination of deceased specimens, and a comprehensive pest control program. Animals should be evaluated to ensure their health complies with local, state, and federal health requirements before shipment to other zoos or before release in managed reintroduction programs. Preshipment evaluations can also be used as an opportunity to assess the overall health status of the group in which the animal has been living.
Animals entering a collection must undergo quarantine. Quarantine facilities should be designed to allow handling of animals and proper cleaning and sanitizing of enclosures. Shipping crates should be cleaned and disinfected before they leave the quarantine area, and the crates’ contents disposed of appropriately. Quarantine facilities require barriers against ingress of potential vectors and vermin. Separate keepers who are skilled at recognizing signs of stress and disease and who will carefully monitor feed intake and fecal characteristics should care for quarantined animals.
Quarantine entry should be strictly controlled. Only essential personnel should be allowed into the quarantine facility. Individuals leaving the quarantine facility should not return to other animal areas without showering and changing clothing. The duration of quarantine should be appropriate to ensure that infectious diseases are not introduced into the permanent collection when the quarantined animals are released to exhibits. Quarantine facilities should follow the “all-in/all-out” principle, ie, if additional animals are added to an ongoing quarantine, the quarantine period should be restarted.
During quarantine, animals should receive appropriate vaccinations and diagnostic testing (eg, tuberculosis, heartworm). They should be examined and treated for ecto- and endoparasites and screened for enteric bacterial pathogens. Before release, animals should receive physical and laboratory examinations, which may include radiographs, serology, hematology, and clinical chemistries. Serum should be frozen for future reference and possible epidemiologic studies. All procedures and results should be recorded in each individual animal’s medical record, which is an essential component of the medical program. Each animal should also be identified by some permanent method (eg, tattoo, tag, band, eartag, transponder) to ensure future identification.
When new animals are introduced to enclosures, caution and forethought are necessary to prevent self-induced trauma. Visual barriers, eg, suspending canvasses from fences or enclosure walls or obscuring glass with soap to provide a visual cue, are standard management steps to protect newly introduced specimens from accidents during acclimation to a new exhibit.
Like domestic animals, zoo animals are vulnerable to a wide variety of ecto- and endoparasites, and similar drugs are used for treatment. Care must be exercised in the choice of medications because of species-specific sensitivities to some drugs. Young animals and those stressed by shipment, disease, or injury are the most likely to be adversely affected by parasites. At these times, commensal parasites (especially protozoa) can cause disease. Acute diarrhea can result from massive infections of coccidia, Trichomonas, Giardia, or Balantidium spp. Amebiasis, which is fairly common in primates and reptiles, can be fatal in a compromised animal. Intestinal parasites may be a major, continuous problem in species kept in naturalistic exhibits or on dirt substrate or pasture, especially in young, newly introduced, or stressed individuals. Of most concern are parasites with direct life cycles. Incorporating anthelmintics directly into the feed is helpful. As in domestic species, anthelmintic resistance may develop and necessitate rotating medication. Parasites with indirect life cycles are less frequently a problem if the exhibit area is free of intermediate hosts.
Vaccination programs for carnivores, nonhuman primates, equids, artiodactylids, and birds should be developed. Vaccination of zoo carnivores is essential because of their susceptibility to various diseases such as feline panleukopenia, feline rhinotracheitis, feline calicivirus, rabies, canine distemper, and canine parvovirus. (Also see Vaccination of Exotic Mammals). Previously, only killed virus vaccines were recommended, but recent studies have shown that some modified-live vaccines are safe for use in select species. Further studies are required, because some modified-live vaccines (especially canine distemper) can result in fatal disease in certain species. A canarypox-vectored recombinant canine distemper vaccine has proved safe for use in those species susceptible to modified-live virus vaccine-induced disease. Appropriateness of rabies vaccination depends on the circumstances of each collection. If indicated in rabies-endemic areas for protection of individual animals, only a killed rabies vaccine should be used. The decision to vaccinate zoo animals for less common diseases for which a vaccine is available should be made on an individual basis. Recombinant and subunit vaccines are being developed for a variety of infectious diseases for domestic animals. Extra-label use of vaccines should be done with caution until safety and efficacy studies have been completed for zoologic species.
All dead animals should be necropsied. This should include gross and histopathologic evaluation of tissue and viral, bacterial, or fungal cultures when appropriate. Tissues should also be saved for potential future examinations. A thorough pathology examination allows evaluation of medical, management, and nutritional programs. It is also valuable in identifying problems requiring immediate action to safeguard the health of the collection. Variations in anatomy should be recorded, because such observations may aid in future diagnostic procedures or therapy in the species.
A successful control program is continual and requires a concerted effort by zoo staff to minimize harborage and food for pests, in addition to the use of mechanical and chemical control methods. Choice of agent, method of use, and storage may minimize zoo animals’ access to pesticides and the risk of secondary poisoning. Common zoo pests may serve as important disease vectors. For example, cockroaches are intermediate hosts for GI parasites of primates and birds; rodents can harbor and spread Listeria, Salmonella, and Leptospira spp and Francisella tularensis. Wild and feral carnivores such as foxes, raccoons, and domestic dogs and cats can devastate animal collections through predatory attacks and may be important vectors for viral diseases such as rabies, parvovirus, and canine distemper. Raccoons may also transmit Baylisascaris parasites, which can cause larval migration, resulting in fatal neuropathy in some species. Pigeons, geese, ducks, and starlings are potential reservoirs for avian diseases; they consume or contaminate animal food and deposit droppings everywhere. Arthropod vectors can transmit pathogens such as West Nile virus.
Some zoos have either a staff nutritionist or a nutritional consultant on contract. Zoos that do not should have some degree of veterinary oversight of diets and diet changes. This is especially true for addition of native or exotic plant species to the diet as browse for either enrichment or as an integral part of the diet. Protocols should be developed for diet formulation, diet changes, and addition of plant material to the diet.