Animal care staff have the first opportunity to identify changes or abnormalities in the animals. In wildlife species, early signs of disease—such as changes in behavior or reduced activity, anorexia, or abnormal feces—may be subtle, masked, and easily missed by the untrained observer. Overzealous reporting of observations is preferable to indifference.
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 humans. 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 as well as understanding any disruptions in social hierarchies should an animal require hospitalization or removal from the exhibit for treatment.
Behavioral Training of Zoo Animals
An active behavioral training program enables improved health care. Positive reinforcement can be used to train zoo animals to perform behaviors on command that facilitate various management or medical procedures. Behaviors that are helpful in management include shifting on and off exhibit, onto scales, and into restraint devices or shipping containers. Medical procedures include urine collection, venipuncture, intramuscular injection, ultrasonographic examination, and physical 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.
For species that need routine medical procedures or husbandry work, positive-reinforcement training can provide safety for personnel, who can deliver care on the opposite side of a protective barrier, and give the animal some scope of choice. For example, elephants can be trained in foot placement for radiographs or cooperate for trunk washes.
Physical Restraint of Zoo Animals
Methods of restraint should be chosen based on the animal's history and temperament, animal care staff experience, and equipment available. Physical restraint should be used only if manual restraint can be performed with minimal risk or if adequate restraint devices, such as squeeze cages or chute systems, are present. Many procedures can be performed on unanesthetized animals under physical restraint, including limited physical examinations, administration of injections (including anesthetic drugs or tuberculin testing), collection of blood samples, or minor hoof trims.
Courtesy of Dr. Meredith M. Clancy.
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. Often, minor noninvasive procedures that do not warrant the time and risk of anesthesia can be performed on small mammals and birds using such physical restraint.
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 humans. Although gloves may limit dexterity, heavy gloves protect handlers from teeth, claws, hooves, horns, and antlers when animals are manually held after capture.
Diagnostic Techniques for Zoo Animals
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, with advanced imaging such as CT scans becoming more common. Endoscopy and laparoscopy allow for minimally invasive diagnostic and surgical access, although technical expertise is required. Virtually any technique used for other species can be modified for use in zoo species.
Drug Administration in Zoo Animals
Most veterinary drugs are not labeled for use in zoo species; however, extra-label use laws allow legal use in species for which drugs are not licensed. Whenever possible, drug administration should be based on pharmacokinetic data, although veterinarians often use medications in species without previous documentation of therapeutic benefit or knowledge of exact dosage, treatment schedule, or contraindications, or toxicity data in those species. In those cases, extrapolation from what is known is necessary. Metabolic scaling has historically been used, although it has important limitations across taxonomy in zoo species. Fortunately, increasing numbers of species-specific pharmacokinetic studies in zoo species allow for more evidence-based use of antimicrobial or anesthetic medications.
Drug administration can be challenging in zoo species. Oral medication may prove challenging in discerning and intelligent species and can be difficult to administer when animals are housed in a group. Antimicrobials administered orally can disrupt the normal flora of foregut fermenters, such as ruminants or macropods. Given the reliability of absorption and administration of drug via the parenteral route, parenteral administration is preferred for many medications, especially sedatives or anesthetics. Parenteral administration may also be preferable if long-acting or depot formulations of medications are available. With behavioral training, many animals voluntarily allow zoo personnel to administer intramuscular injections.
Remote delivery of parenteral medication is commonly performed in the zoo setting when anesthetics or treatments cannot be administered via hand syringe or orally. Remote delivery should be performed by an experienced professional familiar with the equipment and the risks to the animal. Problems can be minimized via 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 using them. Other methods of remote injection include syringe poles or blow guns.
Photograph of appropriate placement of a dart with medication on a southern white rhinoceros (Ceratotherium simum simum).
Courtesy of Dr. Meredith M. Clancy.
Photograph of appropriate placement of a dart with medication in a captive okapi (Okapia johnstonii)
Courtesy of Dr. Meredith M. Clancy.
Photograph of appropriate placement of a dart with medication in a captive Eastern bongo (Tragelaphus eurycerus isaaci).
Courtesy of Dr. Meredith M. Clancy.
Photograph of appropriate placement of a dart with medication on a southern white rhinoceros (Ceratotherium simum simum).
Courtesy of Dr. Meredith M. Clancy.
Photograph of appropriate placement of a dart with medication in a captive okapi (Okapia johnstonii)
Courtesy of Dr. Meredith M. Clancy.
Photograph of appropriate placement of a dart with medication in a captive Eastern bongo (Tragelaphus eurycerus isaaci).
Courtesy of Dr. Meredith M. Clancy.
Intravenous treatment can be provided to zoo species if appropriate measures are taken, including adequate tranquilization or sedation, or containment in restraint devices or small enclosures during treatment. As in domestic animals, in-dwelling intravenous catheters and intravenous treatments are reserved for cases requiring the most intensive treatment, as it can be labor intensive to maintain intravenous access in zoo species. Intravenous access also allows for total intravenous anesthetic administration in some species.
Courtesy of Dr. Meredith M. Clancy.
Anesthesia Considerations for Zoo Animals
Safe administration of anesthesia to zoo animals is of special concern. Many procedures routinely accomplished on domestic animals with minimal restraint require anesthesia of zoo species to ensure welfare and safety of both animals and personnel. Before anesthesia of a zoo animal, the veterinarian should be familiar with the species and anesthetic agents. Anesthesia records for the individual, other specimens of the same species in the collection, or published references for the species should be reviewed. Differences in response to certain anesthetic agents may vary even among closely related species, so consultation with a knowledgeable individual in the field is advised. 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.
The location in which an animal is anesthetized is another important consideration and may influence drug selection. Removing water sources and trip or entanglement hazards may reduce risks; however, if that is not possible, planning for availability of adequate staff and access points to the animal is needed in case early intervention is required, and especially if anesthesia is performed in a herd situation where other animals are present.
The cyclohexamine ketamine is a common anesthetic for small- to medium-sized mammals, especially primates, carnivores, and some ungulates, often given in combination with an alpha2-adrenergic receptor agonist or benzodiazepine. Ketamine is one of the few anesthetic agents licensed for use in zoo animals, with licensure in primates as a single anesthetic agent. Combining ketamine with other drugs reduces the amount of ketamine required and provides a smoother anesthetic induction and recovery than using ketamine alone. Highly concentrated ketamine acquired from compounding pharmacies can reduce drug volume, which is especially important when remote delivery (via dart) is required.
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 administered for anesthesia of carnivores and primates or as a first-line agent in emergency situations because it has a relatively wide margin of safety. Because no complete antagonist exists, recoveries can be longer than with other combinations that can be completely reversed.
Alpha2-adrenergic receptor agonists such as xylazine, detomidine, medetomidine, or dexmedetomidine can be used as sole agents as they are in domestic species; however, more often in zoo species they are administered for their sedative and analgesic effects in combination protocols. The effects of these sedatives can also be antagonized by administration of atipamezole, tolazoline, or yohimbine, making for smoother recoveries and more complete reversals. Reversal using atipamezole is dosed at 5 mg atipamezole to 1 mg medetomidine, resulting in relatively complete antagonism. Re-sedation or recycling has been seen in some species in which higher doses of alpha2-agonists were administered. Species sensitivity to alpha2-agonists can vary greatly, as does the dosage required depending on the combination protocol selected. Alpha2-agonists should not be administered as the sole anesthetic agent in dangerous carnivores, because these animals may appear sedated but can respond aggressively when stimulated. When combined with ketamine, alpha2-agonists can provide a surgical plane of anesthesia in many species and a safe anesthesia in dangerous animals. Combined with an ultrapotent opioid, alpha2-agonists can also provide the basis for anesthesia in many species of hoofstock or megavertebrates; the less potent butorphanol can be combined with an alpha2-agonist to provide adequate standing sedation. Dosage-dependent peripheral vasoconstriction caused by alpha2 adrenergic receptors can lead to alterations in blood pressure, which may interfere with pulse oximetry monitoring or make venipuncture or catheterization more difficult.
Opioids are a mainstay in zoo medicine, both the mixed agonist-antagonist butorphanol and the cadre of ultrapotent opioids, such as thiafentanil or etorphine. Although historically, ultrapotent opioids—including the now unavailable carfentanil—were administered as single agent anesthetics, this is no longer regularly done in zoo animals because of the resultant respiratory depression and muscle rigidity. Instead, these anesthetics combined with other agents (eg, alpha2-agonists, azaparone, acepromazine), 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. The currently recommended ratio for reversal is 50 mg naltrexone to 1 mg of ultrapotent opioid, often administered intramuscularly. Renarcotization is always a risk, requiring repeated reversal if signs of star-gazing, unarresting motion, or other signs are suspected. Renarcotization is less common with thiafentanil than it was with carfentanil, and more common in certain ungulate species (eg, Arabian oryx, slender-horned gazelle) or if remote dart delivery resulted in a "bounce-and-spray" or possible subcutaneous or irregular injection.
Caution and appropriate personal protective equipment are essential when handling ultrapotent opioids or highly concentrated alpha2-agonists. Accidental exposure of humans to ultrapotent opioids is dangerous, and they should be used only by trained and experienced personnel. All staff present during deployment of these anesthetics should receive routine training on protocols for accidental exposure.
The neuroactive steroid alfaxalone has been growing in use in zoo animals, with studies demonstrating safety and efficacy in species ranging from marine invertebrates to fish to reptiles to zoo mammals. Dose-dependent anesthesia with smooth recoveries has been observed in multiple species. Volume can be a limiting factor, with high volumes required for relatively small species. Alfaxalone recently became a controlled drug, like opioids, dissociatives, and benzodiazepines.
The rapid onset and short duration of propofol make it a useful anesthetic if intravenous access is possible, so although as an induction agent, its utility may be limited to certain species, it is quite useful as a supplemental agent for many species. Isoflurane is routinely administered as the inhalation agent of choice for multiple small mammals, birds, and reptiles, or as a maintenance agent in longer anesthetic events. Sevoflurane use has become more prevalent in reptiles recently. Other agents used in combination anesthesia or sedation include the phenothiazine tranquilizer acepromazine or the butyrophenone tranquilizer azaperone.
Many factors influence an animal’s response to anesthetic drugs, including age, sex, health status, and most especially, mental state before drug administration. Even reliable anesthetic protocols repeated in an individual may produce different results given external factors. An excited animal usually requires a higher dosage of anesthetic and, once anesthetized, may have a greater risk of developing capture myopathy. Capture myopathy (also called exertional myopathy) occurs secondary to hyperthermia, metabolic acidosis, and respiratory depression associated with capture or anesthesia and can present with a variety of manifestations. The most commonly seen type of capture myopathy occurs generally as an acute myoglobinuric myopathy ( See also page Capture Myopathy).
Anesthetic monitoring is critical in zoo species and should include at minimum monitoring heart and respiratory rate and temperature. 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), as well as ECG help provide a more complete picture of an animal's physiology under anesthesia. Attention must be paid to appropriate positioning and padding of anesthetized animals and extremes of environmental conditions to prevent secondary complications.
Regulatory Issues Regarding Zoo Animals
Collection, transport, and exhibition of wildlife requires compliance with local, state, and federal laws. Permits may be necessary to maintain these species. Institutions in the US 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 US 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 US. Specific regulatory rules and regulations may dictate management of certain species. For example, robust requirements for tuberculosis testing in captive elephants exist, including requirements for three negative trunk wash cultures collected within a 7-day period performed at a frequency dependent on herd status. These may change based on recommendations from the US Animal Health Association to federal and state agencies. Familiarity with these regulations and relationships with regulatory veterinarians are essential for any practicing zoo veterinarian to ensure compliance.
Zoonoses of Zoo Animals
Zoonoses are an important consideration at zoos for the animals, the staff, and the visiting public. Many diseases in humans are anthropozoonotic, meaning they originated in animals. Wild animals or pets may harbor zoonoses that pose a health risk to captive wildlife, such as raccoons with canine distemper virus or bats with rabies. Mycobacterial infections have zoonotic potential, from atypical mycobacteriosis, important as a wound infection from contaminated water, to tuberculosis, as an anthropozoonosis and zooanthroponosis in elephants, primates, and other mammals. Routine tuberculosis testing should be arranged in conjunction with the zoo veterinarian, the institution's occupational health specialist, and/or the government public health department for those workers in contact with susceptible species.
Chlamydia psittaci can infect birds with minimal clinical signs but may cause disease in humans, especially those who are immunocompromised. Reptiles have been documented to intermittently shed Salmonellaenterica serovars, and other carnivorous species of birds or mammals can also shed this bacteria in their feces. This and other enteric pathogens—both bacterial and parasitic—underscore the importance of appropriate personal protective equipment, such as gloves, and hygiene habits such as frequent handwashing. Tuberculosis infections in mammals, especially primates, ungulates, and elephants, can be transmitted from humans or harbored and shed by animals to infect zoo staff. Recognition of these zoonotic diseases and 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, with adequate biosecurity training and personal protective equipment available. (Also see Zoonoses.)
