Medicine, Surgery and Wildlife, Marathon Veterinary Hospital, Marathon, FL, USA
There is no question that the most common health problems associated with captive reptiles are diet related. These can be from nutritional deficiencies, such as is so commonly seen in the green iguana, excessive calorie consumption, as in overweight animals, or the most common problem, anorexia, or a lack of appetite. There are numerous causes for a reptile to lose its appetite. These underlying causes must be identified and corrected before the problem will be resolved.
When an animal is “off-food” there has to be a reason for it. It may be psychological, or it may be medical. Although this may seem elementary to most readers, it bears mentioning. It is essential that the veterinarian understands the natural history and biology of the particular type of reptile that they are treating. If they do not know, they must have a ready reference source. If one is not available, then, ethically, they should refer it to someone that has the proper training. In order to more easily arrive at a proper diagnosis, a brief discussion of the normal feeding response is in order.
An animal normally eats to satiety. The cessation of the feeding response prior to the satisfaction of caloric needs is termed anorexia. Clinically, this is referred to as an “absence of hunger.” The body is naturally, continuously in a state of hunger. Eating is the process that satisfies or controls that hunger state. The hunger and satiety centers are located in the brain.
Stimulation of the lateral hypothalamus initiates the feeling of hunger. Activation of the ventromedial hypothalamus results in satiety. Several neuroendocrine and metabolic factors affect these feeding control centers. Of clinical importance, the senses of taste and smell play major roles in the triggering of these responses.
There are several factors that play a role in anorexia. The major task of the small mammal clinician when faced with an anorectic reptile is to determine whether the condition is caused by pathologic, physiologic, or psychologic embarrassment.
There are many diseases that can disrupt the normal neurologic, endocrine or mechanical processes involved in the feeding response. A pure division into categories is not possible, as many diseases have components that overlap. In some situations, the cause is obvious (such as gross malocclusion in turtles), and in others, elusive (cancer cachexia).
Categorizing signs and laboratory data may help in assessing the problem. In general, anorexia may be classified as either primary or secondary with respect to disease. In addition, there is a third category, called pseudoanorexia, which is not directly related to suppression of the feeding centers in the brain.
Primary anorexia should be considered in any case where the inciting factor directly involves the feeding centers of the hypothalamus, or from psychological disorders that have a direct impact of neural control of the feeding response.
Any cranial injury or insult, such as trauma, cerebral hemorrhage, cerebral edema or hydrocephalus (acquired or congenital) may cause anorexia. In humans, severe headaches, such as migraines, may be directly responsible for appetite suppression. Diseases or pathology within the cranial vault, such as encephalitis/meningitis or neoplasia, can have a direct or indirect effect on the hypothalamus.
Any such condition, whether primary to the hypothalamus or merely affecting the hypothalamus, may also have other neurological manifestations in addition to anorexia. Thus, a thorough neurological examination, as part of a complete physical evaluation of the patient, is imperative.
Psychological disorders are more easily characterized in people, as our veterinary patients are less likely to articulate their emotional state. As a result, at the risk of anthropomorphizing, it is often necessary to attempt to interpret what the anorectic patient may be “feeling” in a given situation. For instance, although an owner may enjoy taking their pet reptile to the movies, the reptile may respond differently to the darkened, air-conditioned interior of the theater, the bright flashing lights of the projector, the loud responses of the audience and the artificially buttered popcorn.
Anorexia nervosa, a disease common to young human females, has not been documented in animals. “Maladaptation syndrome,” a condition common to recently captive animals, may have some psychological or physiological similarities, but this is not a likely problem in the captive reptile.
Any external influence that incites stress or anxiety (identified as fear or depression in people), such as changes in the environment (temperature, caging, air exchanges, noise etc.) can result in anorexia. Two common psychological influences include the alteration of social structure within the animal›s environment (addition of a new animal to an established group) and the offering of a new food type.
Secondary anorexia includes diseases or influences from outside the brain and have a direct effect on the neuroendocrine control of hunger. Some conditions or diseases may produce signs associated with anorexia such as nausea and vomiting (although the latter is not seen in reptiles). It is believed that the stimuli associated with these conditions are similar and the controlling centers within the brain are most likely neuronally interconnected.
Abdominal pain is a common cause of anorexia in reptiles. Constipation may contribute. Inflammatory conditions, such as coelomitis, hepatic, renal, pancreatic or visceral inflammation can all lead to anorexia by directly or indirectly stimulating the appetite centers.
Exogenously or endogenously produced toxins can affect the appetite by either directly affecting the feeding centers, or indirectly by affecting other areas of the body, such as the abdominal organs. Drugs and toxins can also affect the chemoreceptor trigger zone which produces nausea and anorexia or can act directly on the hypothalamus.
Endogenously produced toxins, such as azotemia or hyperammonemia, as seen in renal or hepatic failure, respectively, have serious consequences on appetite. Hypercalcemia, by yet an unidentified factor, also leads to anorexia.
Neoplasia and cachexia are frequently associated together. However, oftentimes, the cachectic patient still has an appetite. Cancer patients may not always desire food, as the peptides and nucleotides associated with certain neoplastic diseases are known to cause anorexia. Neoplasia should be on the differential list for anorectic patients.
Miscellaneous causes of anorexia should include any systemic illness. Cardiac, pulmonary or pancreatic disease (e.g., diabetes although not well documented in reptiles) can be contributing factors. Lastly, pseudoanorexia, which is a physical inability to eat, rather than the lack of desire to eat, must always be considered with the clinically anorectic patient. Dental disease, or malocclusion as seen in many turtles, is a frequent contributing factor in reptiles.
A thorough physical examination is warranted for every case, including cases with apparent obvious explanations for the anorexia. In addition, a proper cranial nerve examination must be conducted. An open mouth oral examination (using sedation as needed) must be performed.
Equally important as the physical findings is the collection of a thorough history. Discern if there have been any changes to the animal’s environment, including caging, food, conspecifics, ambient temperatures etc.
Radiographs, laboratory analysis (including complete blood counts, serum chemistry analysis and urinalysis) should be a part of every minimum data base. Anorexia and food deprivation have serious consequences on a patient, especially to those that are convalescing.
Tissues such as the brain, the red blood cells, renal medullary cells and neural tissue have an obligate glucose requirement. To maintain blood glucose, body protein is rapidly affected. The ramifications of food deprivation are far beyond the scope of this discussion, but it is obvious that it will have serious consequences.
Anorectic reptiles need to be supported with appropriate diets. Appropriate gruels can be administered via syringe feeding, and when necessary, nasogastric tubes. Attention must be given to the animal’s fluid balance and other medical needs, such as the administration of antimicrobials and analgesics, as required.