The mainstay of the zoo medical program is a qualified and dedicated keeper staff. The keepers know the individual animals under their care and observe them daily. They are the first to recognize abnormalities such as anorexia, inactivity, abnormal feces, or changes in behavior that may reflect early medical problems. Overzealous reporting of observations is preferable to indifference. Because many zoo animals, especially prey species, instinctively conceal overt signs of illness until the disease process is well advanced, it is necessary to make keepers aware of the significance of what may seem to be trivial changes. Past associations with the veterinarian may arouse some animals’ responses to the veterinarian’s presence, which will mask subtle changes noticeable to keepers.
Once a diagnosis is made, the treatment of zoo animals is similar to that of domestic species except in the method of drug administration and restraint. A comparative medical approach is generally most successful and involves application of medical or surgical information about diseases affecting free-ranging animals, related domestic animals, or people. Frequently, other veterinary experts or human medical or dental specialists are consulted for advice or assistance with complicated medical or surgical cases. Knowledge of comparative anatomy, physiology, behavior, nutrition, pathology, and taxonomy is useful. Attention must be paid to both individual and population health.
Unless medical conditions dictate otherwise, it is often preferable to leave an animal under treatment at its home exhibit where it can maintain contact with its conspecifics and keepers. This can also prevent disruptions in social hierarchies, which may cause difficulties with reintroductions to an established group.
An active behavioral training program enables improved health care. Through positive reinforcement, amphibians, reptiles, birds, and mammals in zoo settings have been trained to perform behaviors on command that facilitate accomplishment of various management or medical procedures. Management behaviors include shifting on and off exhibit, onto scales, and into restraint devices or shipping containers. Medical procedures include urine collection, venipuncture, IM injection, tuberculin testing, ultrasonographic examination, and rectal or vaginal examination. Often, these behaviors are incorporated into behavioral and environmental enrichment programs. Enrichment programs are designed to encourage animals to display more of their normal behavioral repertoire, eg, increasing opportunities for foraging or social interaction, which allows animals to spend their time more as they would in nature.
Protected contact, a management system for elephants, uses positive reinforcement to encourage the elephant to present appropriate body parts through openings in a wall. Procedures such as venipuncture from the ear, foot trimming, reproductive evaluation, artificial insemination, and trunk washes are routinely performed using protected contact. This system provides safety for personnel working with elephants and gives the elephant a degree of choice.
Most zoo animals resent being handled and resist manual restraint. Struggling with an animal to administer treatment may do more harm than can be offset by treatment. Physical restraint is indicated in some species for minor manipulation or close observation. Restraint devices (squeeze cages) or chute systems are frequently used for species that are large, dangerous, or difficult to handle. Many procedures can be performed on unanesthetized animals so confined, including limited physical examinations, tuberculin testing, administration of injections or anesthetics, collection of blood samples, trimming malformed claws or overgrown hooves, and application of topical medications.
Although the dimensions and construction of these devices vary, some operate by movement of one wall to restrain the animal against the other. Openings are provided to allow safe access to the animal. Many restraint devices for hoofstock are designed with a “V” shape; once the animal enters, the floor is lowered and the animal’s body is restrained by the “V” with its feet suspended off the ground. Whenever possible, animals should be trained to enter or be enticed, rather than forced, into the restraint device. Ideally, these facilities should be designed as part of the animal’s regular quarters and located in an area where the animal is normally shifted as part of the daily routine. Exhibits should contain nest boxes or restraint pens equipped with doors that operate remotely to confine the animal. From these areas, the animal can be transferred to a restraint device, anesthetic chamber, or shipping container. Weighing facilities are essential.
Small mammals and birds may be caught and restrained in long-handled hoop nets. These nets must be deep enough that the animal can be confined in the blind end, with the upper part of the net twisted to prevent escape.
Personnel participating in capture or restraint procedures must understand their role and be aware of the behavioral characteristics and physical abilities of animals. This is essential to ensure safety of both animals and personnel. Heavy gloves protect handlers from teeth and claws when animals are manually held after capture. Care must be used to avoid excessive pressure on animals, because gloves hinder both dexterity and the perception of the amount of pressure being exerted. Gloves are also difficult to clean and can be a fomite for transmitting infectious agents.
The fundamental diagnostic technique is a good history and thorough visual and physical examination (often requiring anesthesia). Ease of sample collection for laboratory testing (CBC, biochemical profile, serology, cytology); fecal examination for parasites; urine for urinalysis; and aerobic, anaerobic, fungal, and viral culture depends on species anatomic differences. Radiography and ultrasonography are commonly done. Endoscopy, laparoscopy, and minimally invasive surgery are used when indicated, with use of CT and MRI becoming more common. Virtually any technique used for other species can be modified for use in zoo species.
Few drugs are approved for use in zoo species, but extra-label drug use laws allow drugs to be legally used in species for which they are not licensed. Providing quality medical care to zoo animals requires that medications be used without documented therapeutic benefit, dosage, treatment schedule, contraindication, and toxicity data in these species. Whenever possible, drug administration should be based on pharmacokinetic data. If appropriate data are not available, extrapolation from what is known about these parameters in other species using metabolic scaling is necessary. Appropriate dosage is necessary if therapy is to be beneficial, especially with drugs that have the potential for organ toxicity. Antibiotic, antifungal, and analgesic treatments, as well as anesthetic dosages, are becoming less empirical because of increasing species-specific knowledge resulting from pharmacokinetics studies in zoo species. When using a drug on a group of animals for the first time, it is often wise to initially administer it to just one or two individuals. If no adverse effects are seen, the rest of the group can then be treated.
Drug administration can be challenging. Oral medication has the advantage of minimal disturbance to the animal, but ensuring adequate individual intake may be a problem, especially when animals are housed in a group. Mixing the medication with favorite foods or treats is helpful. Oral antibiotics in hoofstock and other species can disrupt normal bacterial flora and lead to GI problems. Oral sedative or anesthetic administration can result in variable onset, duration, and depth of effect because of inadequate consumption or delayed absorption. IM injections with a hand syringe can be difficult unless a restraint device or other means of physical restraint is used. Remote IM injections may be made by firing a projectile syringe from a dart gun. However, these injections may be painful and add the trauma of dart impact and injection, especially when delivering large volumes (eg, 10 mL) over long distances (50 m). Problems can be minimized through careful selection of the most appropriate drug and drug concentration, as well as the type of dart gun for the intended use. In addition, practice with projectile darts is mandatory before their use. Marksmanship and familiarity with the weapon are essential—such weapons in the hands of a novice can be fatal. Other less traumatic methods of IM injection, over shorter distance, include syringe poles or blow guns. Through behavioral training, it is also possible to administer IM injections through voluntary participation of the animal. IV therapy is generally restricted to anesthetized animals or those maintained in restraint devices or small enclosures for the duration of treatment.
Safe anesthesia of zoo animals is of special concern. Many procedures routinely accomplished on domestic animals with minimal restraint require anesthesia of zoologic species for the welfare and safety of both zoo animals and personnel. Before anesthesia of a zoo animal, the veterinarian should be familiar with the species and choice of anesthetic agent. Anesthesia records for the individual, other specimens of the same species in the collection, or published references for the species should be reviewed. Consultation with someone knowledgeable in the field is advised, because there are large differences in effective drugs and dosages in the diversity of species in a zoologic practice. An anesthetic plan should be developed for each anesthetic episode; the plan should include the anesthetic drugs and doses to be used, other needed pharmaceuticals (eg, emergency drugs, analgesics, anthelmintics, vaccines), monitoring equipment, and any other special equipment to perform the procedure at hand.
Many factors influence an animal’s response to anesthetic drugs, including age, sex, stage of reproductive cycle, general nutritional status, and most especially mental state before drug administration. Variations may be marked between species as well as individuals and between different collections of the same species. An excited animal usually requires more drug and, once anesthetized, has a greater tendency to develop capture myopathy secondary to hyperthermia, respiratory depression, and acidosis. Capture myopathy can also occur in manually restrained animals and is more common in ungulates or long-legged birds (see Exertional Myopathy in Poultry : Capture Myopathy). Monitoring of anesthetized animals may include heart and respiratory rates, temperature, ECG, oxygenation (measured by blood gas determination or pulse oximetry), ventilation (measured by blood gas determination or end-tidal CO2), and blood pressure (measured directly or by oscillometric techniques). Attention must be paid at all times to appropriate positioning and padding of anesthetized animals and extremes of environmental conditions to prevent secondary complications.
The nature of an enclosure in which animals are to be anesthetized should be carefully considered before initiation of an anesthetic episode to minimize complications. For example, prey species that are darted may startle and hit fences or other barriers. In herd situations, the herd members may attack and injure or kill the darted animal as anesthetic induction begins (eg, ataxia).
Xylazine, detomidine, or medetomidine (α2-adrenoreceptor agonists) used alone produce adequate sedation in some ungulates, mainly bovids, to allow some manipulative procedures. The sedative effects can be antagonized by administration of yohimbine, tolazoline, or atipamezole. α2-Agonists should not be used as the sole anesthetic agent in dangerous carnivores, because the animals may appear sedated but can respond aggressively when stimulated. Peripheral vasoconstriction caused by these agents alone or in combination with other drugs can lead to significant hypertension, so blood pressure should be monitored. Peripheral vasoconstriction may also interfere with monitoring pulse oximetry and can make venipuncture more difficult.
The cyclohexamine ketamine (either alone or in combination with tranquilizers or sedatives such as xylazine or medetomidine) is a common anesthetic for small to medium-sized mammals, especially carnivores, primates, and some ungulates. A concentrated ketamine preparation (200 mg/mL) can be obtained from compounding pharmacies, with a resultant decrease in the required injection volume. Combining ketamine with a sedative or tranquilizer speeds induction, minimizes excitement, increases muscle relaxation, and provides a smoother anesthetic induction and recovery than using ketamine alone. The ability to reverse the sedative effects of xylazine or medetomidine with the antagonists yohimbine, tolazoline, or atipamezole enables the use of a lower ketamine dosage and a more complete and rapid reversal after the procedure has been completed.
Tiletamine-zolazepam, a dissociative anesthetic-tranquilizer combination, is relatively safe in most species, has a rapid induction, and can be concentrated to 200 mg/mL to allow a small delivery volume. It is commonly used for anesthesia of carnivores and primates. However, a disadvantage of this drug combination is that no complete antagonist exists; therefore, recoveries can be longer than with other combinations that can be completely reversed.
The rapid onset and short duration of anesthesia induced by the sedative-hypnotic propofol renders it particularly attractive for use in zoo species. However, because of the necessity for IV administration, its use is limited to species such as reptiles, birds, and small mammals that can safely be manually restrained for drug administration. It is also useful as an adjunct anesthetic agent in large mammals first immobilized with another drug combination.
The potent opioids etorphine, carfentanil, and thiofentanil, alone or in combination with other agents (eg, azaparone, acepromazine, xylazine, detomidine), have been used extensively for anesthesia of ungulates, elephants, and rhinoceros. The antagonist of choice for these opioids is naltrexone, a pure narcotic antagonist, which induces complete reversal when given at 100 mg of naltrexone per mg of opioid. The reversal dosage of naltrexone can be given IV or IM, and in species prone to renarcotization after reversal, additional naltrexone may be administered SC. It can also be given IM 6–8 hr later by remote delivery to prevent renarcotization when the animal is not being observed. Accidental exposure of people to ultrapotent narcotic analgesics is quite dangerous. Therefore, they should be used only by trained, experienced personnel, and only after development of accidental exposure protocols.
Various drug combinations (using ketamine, telazol, medetomidine, detomidine, butorphanol, midazolam, diazepam, or xylazine) have been developed for specific species and purposes. Administration to novel species should be undertaken with care.
Isoflurane has become the inhalation anesthetic of choice for small mammals, birds, and reptiles. It is also used as a supplement to an injectable anesthetic or as an anesthetic maintenance agent to prolong anesthesia in virtually all species. Isoflurane is safe and potent and has minimal adverse effects, short induction, and quick recovery periods. Sevoflurane has the advantage of even shorter induction and recovery periods and may be preferred over isoflurane in some species. Small animals can be induced with a face mask or placed in an anesthetic chamber. Inhalation anesthesia can be maintained or supplemented using a face mask, nasal cannulae, or intratracheal intubation, depending on the species and anesthetic plane.
Collection, transport, and exhibition of wild animals requires compliance with local, state, and federal laws. Permits may be necessary to maintain these species. Institutions in the USA must comply with appropriate rules and regulations such as those of the USDA, United States Fish and Wildlife Service, National Oceanographic and Atmospheric Administration, and National Marine Fisheries Service. Some specific health requirements in the USA include compliance with the USDA’s Animal Welfare Act and CDC regulations governing importation of primates and maintenance of colonies of captive bats. The Drug Enforcement Agency governs the purchase and use of controlled substances in the USA. Specific regulatory rules and regulations may dictate management of certain species. As an example, in the USA, the USDA requires that elephants have three negative trunk wash cultures for tuberculosis during a 12-mo period, collected on separate days, preferably during a 7-day period.
Many human infectious and parasitic diseases are of animal origin, ie, are zoonotic. Free-ranging and captive wild animals may harbor zoonotic diseases that pose a potential health risk for those who work with these animals. Reptiles are commonly asymptomatic carriers of Salmonella spp. Avian species may be infected with Chlamydia spp. Tuberculosis infections in mammals, especially primates, ungulates, and elephants, can be transmitted from people or harbored and shed by animals to infect zoo staff. Many enteric bacterial or parasitic pathogens of primates can be transmitted to people. Bats may be a source of Histoplasma spp or rabies. Carnivorous species of reptiles, birds, and mammals that consume uncooked meat-based commercial diets or whole prey may develop an asymptomatic Salmonella carrier state. Numerous zoo species, as well as feral domestic or native species on zoo grounds, may harbor Leptospira spp, Baylisascaris, etc. Recognition of these zoonotic diseases and institution of procedures to minimize the disease risk to zoo staff and the visiting public are important components of a zoologic practice. An occupational health program should be developed for personnel coming in contact with collection animals. Personal protective equipment (eg, disposable gowns, gloves, face shields) should be used as required by zoo personnel. Frequent hand washing is also recommended. (Also see Zoonoses.)