Preventive Medicine for Zoo Animals

Quarantine of new animals entering a collection is a routine practice in zoos to reduce risk of introducing parasites or disease. Historically, it has been a set period (generally 30 days) in a facility or area separate from the zoo's collection and paired with a complete examination to allow for baseline diagnostics and treatments, including vaccinations. The principles of quarantine emphasize biosecurity with facilities to allow handling of animals and proper cleaning and sanitizing of enclosures. Facilities should provide appropriate barriers against vectors and vermin. Shipping crates should be cleaned and disinfected before they leave the quarantine area, and the crates’ contents disposed of appropriately.

Quarantine entry should be strictly controlled. Individuals leaving the quarantine facility should not return to other animal areas without showering and changing clothing. Separate keepers should care for quarantined animals to monitor for signs of stress, disease, or maladaption.

More recently, risk-based assessment of animals entering a collection has allowed for individualized quarantine processes. Risk is based on the animal's origin and sending institution's medical and husbandry history. After thorough review of the animal's record, appropriate and targeted diagnostics and intervention can be planned during the designated quarantine period. 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, such as 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.

Comprehensive parasite control is an integral part of any zoo preventive medicine program. Zoo animals are vulnerable to endo- and ectoparasites, and parasite management includes veterinary and husbandry interventions. Veterinary intervention has classically relied on antiparasitic drugs used in domestic species, with medications selected carefully because of species-specific sensitivities to certain drugs (eg, fenbendazole toxicity in pelicans, porcupines, pigeons, and others). Morbidity and mortality from parasites can be increased during times of stress, such as shipment or when comorbidities are present, or in young animals. 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, and can be fatal in a compromised animal.

Husbandry management of parasites in enclosures includes understanding of parasite life cycle and interruption of this cycle—most commonly by removing feces from the field or eliminating intermediate hosts. Adjunct treatments, including incorporating nonpharmaceutical treatments such as tannins, nematophagous fungi, or copper oxide wire into food, and management strategies such as field rotation, can help in parasite control.

Vaccination to prevent infectious diseases is an important pillar in the preventive medicine program of all zoo animals. Protocols for zoo mammals are varied but most are guided by institution and taxon advisory groups. Nearly all vaccine use in zoo species is extra-label. Core vaccines in zoo mammals most commonly include rabies, tetanus, or clostridial vaccination, and viral pathogens specific to taxa, such as viral respiratory pathogens in felids, and encephalitides in equids. Vaccination in zoo birds most often is against West Nile virus in susceptible species in endemic areas.

Previously, only killed virus vaccines were recommended because of vaccine-induced disease (especially canine distemper virus) in certain species; however, recent studies have shown that some modified-live vaccines are safe for use in select species. A canarypox-vectored recombinant canine distemper vaccine has proved safe for use in those species susceptible to modified-live virus vaccine-induced disease. The decision to vaccinate zoo animals for less common diseases for which a vaccine is available should be made on an individual basis with considerations for geographic area and disease risk.

Postmortem examination is an essential part of health monitoring of zoo animals and zoo collections. Complete examination of all dead animals within a collection is an important part of surveillance. Examination of wildlife found dead on zoo grounds also serves to monitor for infectious and other disease trends. Complete postmortem examinations include gross evaluation of the carcass with histopathologic evaluation of tissue; tissues should be saved for potential future examinations. Further testing may include bacterial or fungal culture with viral testing or special staining. Postmortem examination as part of a thorough pathologic examination, including medical, husbandry, and nutritional history of the animal, is valuable in identifying problems requiring immediate action to safeguard the health of the collection and trends over time. Given the limited existing knowledge regarding some species in zoo collections, complete postmortem examinations can also add to the canon of literature about what is normal and how species vary.

Zoos should practice integrated pest management and have an established program. Multiple methods are required to provide the most effective pest control; for example, elevating food dishes to keep pests out of food, trapping on the periphery of exhibits, and providing bait in protected areas can help reduce rodent pests. Veterinarians should advise on and, if needed, administer any chemical agents, with knowledge of how best to protect collection animals against possible toxins or accidental exposures.

Common zoo pests may serve as important disease vectors. For example, cockroaches are intermediate hosts for 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 via 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. Noncollection birds can carry avian diseases, and open-air ponds attract so-called freeloaders, who consume animal food and contaminate enclosures with droppings. Arthropod vectors can transmit numerous pathogens to vertebrates.

In the absence of a qualified (board-certified) veterinary nutritionist or consultant, zoo veterinarians should provide oversight of diets and diet changes. Protocols should be developed for diet formulation, diet changes, and the addition of plant material to the diet. Veterinarians should be consulted when new browse items or other dietary items are to be introduced, to avoid inadvertently introducing toxins. As part of a more holistic approach to nutrition, animal body condition, diet consumption, and any nutritional diseases or conditions should be routinely evaluated. Animals under human care should be provided a diet as close to their natural feed and feeding strategy as possible to maximize their choice and control and ability to thrive.