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Common Disorders and Procedures of Zoo Animals

By Michael R. Loomis, DVM, MA, DACZM, North Carolina Zoological Park

In general, the disease processes and treatments of zoo species are similar to those of domestic pets, agricultural species, laboratory animals, or people. Commonly encountered medical problems include acute or chronic gastroenteritis, traumatic injuries (bite or gore wounds, lacerations, fractures, luxations), localized (abscess or cellulitis) or generalized (septicemia) bacterial infections, parasitic infestations, obstetric problems, lameness, arthritis, and GI foreign bodies.

Avian Aspergillus infection generally results in chronic respiratory tract disease (see Aspergillosis). Affected birds may exhibit weight loss, markedly increased WBC counts, and in later stages, dyspnea. Death can also occur peracutely if there is a localized aspergilloma that occludes the trachea or in cases of fungal septicemia. Necropsy generally demonstrates extensive fungal granulomas in the air sac and lungs. Species that are more sensitive to Aspergillus infections are penguins, pheasants, and waterfowl. Treatment is generally unrewarding because of the advanced state of infection when diagnosed but can include oral (flucytosine or itraconazole), IV (amphotericin B), or nebulized (enilconazole) antifungal medications.

Infectious pododermatitis (bumblefoot) is a common disorder of birds. It can be either unilateral or bilateral and is characterized by lameness, inflammation, and swelling of the footpad due to localized bacterial infection. Sequelae of infection can include chronic pododermatitis, septicemia, or amyloidosis. It can occur due to injury, infection, inappropriate substrate, obesity, or unilateral limb problems (trauma, arthritis) that result in excess and abnormal weight bearing on the contralateral foot. Treatment includes correction of the primary problem, local and systemic antibiotic and symptomatic treatment, and in more advanced cases, surgery.

Avian mycobacteriosis is a chronic problem in many bird collections, and control measures are difficult, because premortem tests are unreliable (see Tuberculosis). Aggressive sanitation of the infected enclosures and culling of infected and exposed birds may help limit disease dissemination but will not eliminate it. Marsupials and young primates may also develop infection when exposed to infected birds or contaminated environments (such as in a mixed species exhibit). The disease in marsupials can manifest by development of lung or bone lesions and is resistant to most therapies. The disease in primates is often benign but may result in nonspecific tuberculin test responses.

Prevention of flight in birds is accomplished by amputating one wing just distal to the radiocarpal joint (pinion) or less commonly by performing a tenectomy and fusing the radiocarpal joint. Pinioning of young birds soon after hatching is easier and more successful. The appropriateness of performing this procedure on birds is controversial. (See also Routine Grooming Procedures et seq.)

Bone fractures are repaired with splints, casts, surgical fixation, or a combination of these methods. Because maintaining a splint on a zoo animal can be difficult, rigid internal fixation or an external fixater are preferable. For best results, fixation should be rigid, strong, and require minimal postoperative care. Because casts must be left in place for 6–8 wk, freedom of movement and a minimum of discomfort must be assured. Newer lightweight, strong, waterproof, fiberglass casting material is especially useful.

Mammalian tuberculosis still occasionally occurs in zoo collections, and routine screening of primates, hoofstock, elephants, and keeper staff is indicated (see Tuberculosis and other Mycobacterial Infections). Interpretation of intradermal tuberculin tests can be problematic in nondomestic species because of the occurrence of nonspecific responses. When a test is suspicious or positive, a complete health evaluation should be performed, including additional tests such as radiographs and gastric and bronchial lavage for mycobacterial cytology and culture. Diagnostic immunologic tests are available for zoo bovids and cervids and include lymphocyte stimulation tests and ELISA. Other tests under development include antigen 85 and γ-interferon testing. The incidence of elephant-to-human transmission of tuberculosis has increased in recent years. Most cases of tuberculosis in elephants is caused by Mycobacterium tuberculosis; however other species, including M bovis, have caused clinical disease in elephants. Asian elephants are more frequently infected than African elephants. Clinical signs are nonspecific and usually present only in advanced cases; they include chronic weight loss, anorexia, weakness, exercise intolerance, discharge from the trunk, cough, and dyspnea. Definitive diagnosis is by culture. Screening by serologic testing, including immunochromatographic (lateral flow), multi-antigen print immunoassay, and dual path platform test, are not confirmatory and are not used as definitive regulatory tests. The USDA has established testing and treatment protocols for captive elephants in the USA.

Hoof and nail trims are necessary when overgrowth occurs and are most often required in ruminants, equids, elephants, rhinoceros, and larger carnivores. These procedures should be conducted on a regular basis to avoid excessive overgrowth. On occasion, the services of an equine farrier are used for more complicated cases such as when an equid has foundered. Elephant foot care is especially important to prevent chronic musculoskeletal problems and can usually be accomplished in an awake elephant through training. Many other species require chemical immobilization for foot care.

Mandibular osteomyelitis (lumpy jaw) is a common problem of small ruminants and macropods (wallabies and kangaroos). It can occur secondary to coarse feed, oral trauma, or dental disease. Animals generally present with localized facial swelling and a foul oral odor or discharge. Treatment consists of lancing the abscess, debriding infected bone, removing affected teeth if indicated by radiographs, and treating with systemic antibiotics.

Dentistry in zoo animals presents unique problems. The roots of canine teeth in primates and carnivores are more extensive than the exposed crown. Simple traction and rotation cannot remove such teeth intact; dislodging with a dental elevator is essential. A small electric drill or bone chisel is used to remove a section of alveolar bone around the root. Root canals are indicated when a large canine tooth is fractured and viable pulp exposure occurs. Specialized long dental instruments are required to remove the nerve tissue from these elongated canals. The incisor teeth of rodents, such as beavers, porcupines, and capybaras, grow continually; unless these animals are supplied with coarse feed or logs to gnaw on, their incisors grow excessively and interfere with their ability to feed. Periodontal disease in zoo animals is treated by routine cleaning (under general anesthesia) and by providing adequate chewing substances to supplement the soft, prepared diets fed to many zoo animals.

Because of excellent management, husbandry, nutrition, and veterinary care, many zoo animals live to advanced ages. Care of geriatric specimens is becoming increasingly common, including such disorders as diabetes, heart failure, chronic arthritis, and neoplasia. The same diagnostic and therapeutic principles of management of these disorders in people or domestic animals may be successfully applied to the care of affected zoo animals.

Elephant endotheliotropic herpesvirus infection (EEHV) is one of the most significant disease threats to captive elephants. Several virus types that cause disease have been described, although viral latency is common. EEHV primarily causes acute hemorrhagic disease, mostly in young Asian elephants (Elaphas maximus) with a mortality rate of up to 85%. Clinical signs are predominately nonspecific and include lethargy, anorexia, mild colic, and tachycardia. There is often edema of the head, neck, trunk, and thoracic limbs. Cyanosis of the tip of the tongue that progresses caudally and hemorrhage of the tongue and oral ulcers are also seen. Antemortem diagnosis is currently made by PCR analysis of whole blood. Early, aggressive treatment with antiviral agents (famciclovir or ganciclovir) with good supportive care has decreased the mortality rate since 2009.

Since the emergence of West Nile virus in the USA in 1999, it has been detected in 22 orders of birds, 8 orders of mammals, and 2 orders of reptiles. Mammals showing clinical infections in zoos include alpacas, sheep, reindeer, harbor seals, Indian rhinoceroses, a polar bear, a wolf and several domestic canids, a Barbary macaque, white-tailed deer, and a killer whale. Clinical signs have also been seen in alligators.

Highly pathogenic avian influenza (HPAI) is a threat to zoo bird collections. Zoos should develop HPAI response plans and establish a dialogue with state and national agricultural regulatory agencies to mitigate the impact of HPAI on zoo collections.