Hepatic Lipidosis in a Black-Headed Python

Vet Clin Exot Anim 9 (2006) 589–598

Hepatic Lipidosis in a Black-Headed Python (Aspidites melanocephalus) Mark Simpson, BVSc, MACVSc Sugarloaf Animal Hospital, 67 Carrington Street, West Wallsend, NSW, Australia 2286

Hepatic lipidosis (HL) is a common disease condition of captive reptiles. HL is an endpoint for a number of conditions of metabolic derangement that affect the liver. A modification of Thomson’s original definition of HL (as cited by Carlton and McGavin [1]) as ‘‘an excessive, pathological accumulation of lipid in hepatocytes’’ best describes the main features of the condition in reptiles. It is likely that species-specific predisposing factors lead to HL. Many of the predisposing factors leading to these metabolic de- rangements may result directly from aspects of captive husbandry. Some species may be at more risk for this type of hepatopathy than others. Australian pythons of the genus Aspidites (the woma, A ramsayi, and the black-headed python, A melanocephalus) are highly prized captive snakes. In the wild these snakes can be ophiophagous, that is, they eat snakes, as well as lizards and small rodents (Fig. 1). These prey items are generally small and lean, if not emaciated. Black-headed pythons and womas have a low fasting metabolic rate, even in comparison with other pythons [2]. They have evolved to inhabit some of the most unreliable environments in Australia and even in good years may only feed four times. They are active hunters but can, at times when it is metabolically appropriate, spend long periods (even months) im- mobile. In captivity these snakes are generally maintained on diets of rats and rabbits fed weekly to monthly, and they are rarely exercised. These factors are likely to predispose members of this genus in captivity to obesity, and hence to HL, at a greater rate than other reptiles.

Case report A 7-year-old, captive-bred female black-headed python was presented for lethargy and anorexia. This snake was part of a large collection owned by an experienced herpetoculturist. It was kept in a wooden box measuring 1800 mm

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Fig. 1. A black-headed python (Aspidites melanocephalus) consuming a juvenile lace monitor (Varanus varius), demonstrating the importance of reptile prey to this species in the wild. (Cour- tesy of John Weigel.) long, 750 mm wide, and 750 mm high. Heat was supplied by a 60-Watt incandescent globe at one end of the enclosure, so that immediately be- neath the globe the temperature was 34C, and at the cool end the thermal gradient dropped to 24C. The snake had been routinely treated annually for ascarids with fenbendazole, and previous routine fecal flotation tests had shown no evidence of parasites. Approximately 7 months before presentation, the snake had been cooled for 8 weeks with a view to stimulating reproductive activity. Cooling was ef- fected by leaving the enclosure light off so that the enclosure was maintained at 24C, which was the background temperature of the snake room. In the previous two breeding seasons, this snake had successfully mated, become gravid, and laid two clutches, each of eight eggs, which had successfully hatched. Although in previous seasons this snake had had an observable ovulation associated with successful reproduction, no evidence of ovulation had been detected in the 5 months since warming. The snake was normally fed a large rat every 10 days. Feeding ceased on cooling, so no prey were offered at this time. The snake failed to resume eating on warming, and, despite attempts to stimulate appetite with novel prey items and altered thermal environment, it remained anorexic. On presentation, therefore, it had not eaten for 7.5 months. No history of other health issues existed. On physical examination, the snake had a snout-vent length (SVL) of 1880 mm, weighed 8.2 kg, and was assessed as being obese. Muscle tone was mildly decreased. Droppings were eliminated during examination and demonstrated significant biliverdinuria, with scant fecal component. Other physical findings were unremarkable. HEPATIC LIPIDOSIS IN A BLACK-HEADED PYTHON 591

Cloacocolonic lavage performed at presentation was unremarkable, with no parasites or their eggs detected. Special attention was given to examination for flagellate protozoa and Entamoeba, but none were found. A hematocrit performed at presentation revealed a packed cell volume of 0.31 L/L and a distinct green discoloration to the serum, indicating a biliverdinemia. A complete blood count demonstrated a normal erythron and unremarkable white cell population. Biochemistry revealed modest elevations of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and cholesterol, as well as mild decreases in total protein and glucose. A hepatopathy was considered most likely, and the snake was taken to surgery to obtain a liver biopsy to establish a definitive diagnosis. The snake was premedicated with 3.2 mg butorphanol, injected intramuscularly. After 30 minutes, an uncuffed 3-mm endotracheal tube was placed, and anesthesia was induced with manual intermittent positive pressure ventilation (IPPV) every 15 seconds with 4% isoflurane in oxygen. Once the snake was anesthetized, the left jugular vein was cannulated and the cannula connected to a warmed bag of Ringer’s solution delivered by fluid pump at 8 mL/h. Anesthesia was maintained using IPPV every 20 seconds with 2.8% isoflurane in oxygen and was monitored using an ultrasonic Doppler flow detec- tor (Parks Medical Electronics, Aloha, Oregon) to assess cardiac blood flow. Using the tables of McCracken [3], which provide a ratio of the SVL for each organ in the body, the liver was estimated to lie on the right side of the coelom, between 840 mm and 865 mm from the snout. This area was prepared for sterile surgery. A 35-mm paramedian cutaneous incision was made in a scalloped pattern between the first two rows of lateral scales immediately dorsal to the ventral scutes, beginning about 850 mm from the snake’s snout. The muscle of the body wall was incised parallel, and approximately 3 mm ventral, to the skin incision to avoid the tips of the ribs. The liver was immediately exposed, and three wedge biopsy specimens were col- lected and placed in 10% phosphate-buffered formalin. Hemorrhage was minimal and easily controlled with digital pressure. The muscle layer was closed with single interrupted sutures of 4/0 mono- filament polyglyconate (Maxon, Syneture, Zaltbommel, The Netherlands) and the skin closed to effect eversion using horizontal mattress sutures of the same material. The snake was then ventilated with room air once a min- ute, until spontaneous ventilation began about 12 minutes later. The snake was extubated and placed in a special recovery cage with the temperature maintained at an even 30C across the enclosure. After gradual recovery for 6 hours, surgical fluid therapy was discontinued and the jugular cannula removed. After 36 hours, the snake was transferred to a hospital cage with similar thermal characteristics to the snake’s usual enclosure. A 120-mm deep bed of pelletized, recycled newspaper kitty litter (Breeders’ Choice Cat Litter, FiberCycle, Toowoomba, Australia) with a topping of dried eu- calyptus leaves was provided so that the snake could hide. 592 SIMPSON

Histopathologic examination of the liver biopsy specimens revealed marked generalized lipidosis, with moderate portal fibrosis. Occasional mononuclear inflammatory cells were found in the portal areas, as was considerable bile pigment accumulation in macrophages, attesting to the chronic nature of the pathologic condition. Eight days after coeliotomy, enteral nutrition was begun using a carnivore recovery diet (A/D, Hill’s Pet Nutrition, Baulkham Hills, Australia) mixed with an equal volume of 50% dextrose in water (Baxter Healthcare, Toon- gabbie, Australia) to make a slurry and warmed to 30C. Eighty milliliters of this slurry were delivered by soft, red rubber gavage tube (Cook Veteri- nary Products, Toowoomba, Australia) to the midesophagus, approximately 600 mm from the snout. Gentle handling and gravity (encouraging the snake to climb up a branch) were employed to move the slurry to the stomach. This process was then repeated weekly for 5.5 months. Crushed and mixed with the slurry at the first instance, and once each month thereafter, were 2 g of carnitine and 500 mg of methionine. At the time of the initial tube feeding, 100 mg of vitamin C and 0.3 mL of vitamin B complex were administered intramuscularly. Each week, on the day before gavage feeding, the snake was taken onto the lawn and encouraged to wander in the sunshine for 30 minutes. The snake would consistently head toward a low, dark garden border, which it presumably felt would provide cover. By gently and repeatedly picking the snake up and placing it in the center of the lawn, one could make it move actively for the entire 30 minutes. The snake completed ecdysis twice during recovery, at 4 and 7 months after surgery. The shed skin had to be moistened and removed manually from the surgical site the first time, but subsequent shedding was uneventful. Twenty-three weeks after the biopsy and 10 days after the last gavage feed, a killed mouse was offered as prey and was eagerly consumed. It had been 12 months since the snake’s last voluntary meal. The snake’s weight at this time was 7 kg. A recommendation was made to the owner at this stage for a repeat of the liver biopsy, but it was declined. The snake was fed a pre-killed adult mouse every 21 days for the next 12 months. It was examined at that point, before cooling to stimulate reproductive activity, and found to weigh 6.6 kg. Complete physical examination revealed a normal snake. Droppings at this time were normal, with unstained urates and normal feces. After cooling for 8 weeks, the snake was mated and produced five fertile eggs. It was then recommended to the owner that the snake be fed a pre-killed lean adult mouse every 6 weeks and that the snake’s weight be monitored closely.

Discussion The liver of reptiles, like that of other vertebrates, is responsible for a variety of important functions within the body, including metabolism of HEPATIC LIPIDOSIS IN A BLACK-HEADED PYTHON 593 carbohydrates and fats, synthesis of proteins and vitamins, storage of vitamins and iron, production of coagulation factors, and removal and excre- tion of some toxins. Because the liver is involved in many crucial biologic functions, reptiles with liver disease may show a wide variety of often nonspecific signs, including lethargy, anorexia, weight loss, weakness, vomiting, diarrhea, and behavioral changes. Unlike higher vertebrates, reptiles do not store fats subcutaneously (because it would be an impediment to thermoregulation), so fats are stored primarily in the fat bodies in the caudal coelom. In times of plenty, the fats are absorbed from the diet and transported by the hepatic vein to the liver as free fatty acids. Once at the liver, they are esterified to triglycerides, bound to lipoproteins, and transported to the fat bodies, where they act as a storage form of energy to be used during such normal metabolic activities as brumation or vitellogenesis or during pathologic states. Reptile liver function has not yet been studied in fine detail, and this pau- city of data sometimes makes clinical interpretation difficult. Many of the species’ idiosyncrasies have yet to be elucidated. Moreover, the marked change in the liver of female reptiles in response to reproductive activity makes diagnosis of HL difficult. Obesity is a frequent finding at anamnesis in Aspidites spp that are sub- sequently diagnosed with HL. Like most large, valuable pythons, these snakes may be ‘‘power fed’’ to attain reproductive size and maximum fecun- dity as quickly as possible, and at the same time kept in enclosures that se- verely limit their ability to exercise. Their peculiarly slow metabolic rate and possible adaptation to poor-quality nutrition may place them at greater risk for obesity than other pythons. Professional herpetoculturists in the United States have begun discussing the possibility that the accepted wisdomd namely, that generous girth and high productivity are linkeddmay specifi- cally be wrong in these pythons. Furthermore, herpetologists working in the field in Western Australia report body weights of no more than 2.3 kg for wild black-headed pythons of comparable length to the specimen in this case study (John Weigel, personal communication, 2006), emphasizing the dramatic amount of extra weight that this and many other captive specimens are forced to carry. Although no surveys have been published assessing the reasons for which snakes suffering HL are presented to veterinarians, anorexia is likely to be one of the most common. Anorexia can be a difficult clinical sign to charac- terize, especially in some large snakes, which may go off their food for several months as a matter of routine. It is often difficult to be certain of the primary inciting cause of the anorexia. But, whether it is HL or some other pathologic condition, there is no doubt that in predisposed snakes it causes the metabolic cascade within the liver to snowball precipitously. Interestingly, the signalment in this case was that of a reproductively active female. This case is unusual, because much of the literature reports that adult to aged nonbreeding female reptiles are overrepresented in the groups 594 SIMPSON suffering from HL. Alterations to hepatic and lipid metabolism made in preparation of folliculogenesis and vitellogenesis in reproductively active female reptiles offer the liver some protection from the damage caused by high concentrations of fats. In the course of normal reproductive metabolism, the accumulated lipids are suddenly drained to the reproductive tract for folliculogenesis and vitellogenesis, relieving the protective mechanisms of a chronic role. In females that build up hepatic lipid stores in anticipation of reproductive use that never occurs, chronically high concentrations of hepatic lipids may exceed the ability of the protective metabolic changes to prevent damage to the liver. Although no studies demonstrate a direct rela- tionship, one can intuitively envision this metabolic status of nonbreeding female snakes cascading into HL. The minimum database for any case of HL should include hematology and biochemistry, both for the purposes of definitive diagnosis and planning for supportive therapy, particularly fluid therapy. In this case, the results of clinical pathology were highly suggestive of a hepatopathy. The clinicopath- ologic features characteristic of liver disease in reptiles have been reviewed in detail by Divers [4]. In most HL cases, hematology will inconsistently reveal anemia (which may be complicated by severe dehydration). Acute, or acute on chronic, inflammation of the liver often produces a dramatic heterophilia and monocytosis. Other changes may well reflect the chronic underlying disease, and even chronic bacterial hepatitis may lead to the slightest rise in white cell count. As in the present case, however, hematology may be entirely within normal limits. Biochemistry will often reveal elevations in AST, gamma glutamyltrans- ferase, alkaline phosphatase, ALT, and lactate dehydrogenase, but none of these are truly liver-specific enzymes in reptiles. As a result, elevations must be interpreted in the light of other analytes and of the other clinical findings. Bile acids are often useful in higher vertebrates, but there are technical issues in the application of tests to reptiles that render their interpretation difficult. Both bile acids assays and stimulation tests may prove useful in the future, but at this time they are of uncertain value. Biliverdin is the primary bile pigment produced in reptiles, as it is in birds. Unfortunately for clinicians in both fields, there are no commercial assays for this metabolite. Diagnostic imaging is probably more useful clinically for working up aspects of predisposing disease processes than those of HL. There may be ra- diographically evident changes in the size of the liver, but radiographs usually give little additional, specific, useful diagnostic or therapeutic information in cases of HL. Biopsy, whether performed endoscopically or during coeliotomy, is the most useful diagnostic modality in HL cases. In addition to being diagnostic, hepatic biopsy offers the possibility of identifying underlying disease processes. Such identification makes it possible to tailor therapy more spe- cifically, which in turn is likely to produce more successful outcomes. Al- though a specific underlying disease process could not be identified in this HEPATIC LIPIDOSIS IN A BLACK-HEADED PYTHON 595 case, quantifying the extent of HL and concurrent liver changes permitted a reasonable expectation of response to treatment. As well, this case demonstrates that treatment for HL in Aspidites spp pythons can be a long and arduous undertaking. The owner’s dedication and confidence in his or her veterinarian are essential prerequisites to initiating treatment in these cases. As in many diseases of reptiles, prediagnostic, nonspecific supportive treatment is critical to the success of HL cases. In HL cases, supportive treatment has the added benefit of leading effectively to postdiagnostic specific treatment. Prediagnosis supportive treatment comprises two main aspects: appropriate fluid and nutritional therapy and provision of the appropriate preferred optimal temperature zone (POTZ) that will optimize metabolic and immune function. In the case of members of the Aspidites genus, specific differences in nutritional therapy and unusual characteristics of thermoregulation must be considered. These snakes have one of the lowest basal (or fasting) metabolic rates among Australian pythons [2]. Once fed, their metabolic rate rises to approximately the postprandial values for other Australian pythons. The size of the meal is not recognized as a factor in changing the degree of metabolic rate change, and it only makes a small difference in the duration of metabolic rate change. Hence, when these snakes are fed small, frequent meals, their metabolic rate spends more time at the higher postprandial level than it would if they were fed a large meal less frequently. In the case of this snake, it would have been ideal to maintain this higher metabolic rate status until the liver had recovered, then to use a dramatically lower-frequency feeding schedule for maintenance. Because the owner did not permit repeat biopsies, the time when the liver was likely to have returned to normal was estimated, and a maintenance feeding schedule was then recommended. It is surprising, given the distribution of these snakes in the wild, across the hot northern part of Australia, that they have the lowest POTZ of any Austra- lian python. In the wild, studies have revealed that Aspidites snakes maintain their body temperatures at 28.1C. Temperatures in excess of this, without re- spite from an appropriate gradient dropping below 28.1C, may well interfere with normal metabolism to the point where normal lipid pathways are de- ranged and HL could develop. Ecologic studies also reveal that these snakes spend a significant amount of time buried in substrate with only their heads exposed. An absence of suitable substrate in which to hide may impose a phys- iologic stress and prevent appropriate thermoregulatory behavior. When the patient is showing mild signs of disease and fairly good body condition, and clinical pathology suggests minimal changes to hydration status, then oral fluids are ideal. Any of the electrolyte replacement solutions administered by gavage is suitable. When snakes are ill with advanced HL, intracoelomic or intravenous fluids are more appropriate. Nutritional therapy is the cornerstone of the treatment of HL. It is important to estimate caloric requirements, but in a practical clinical setting 596 SIMPSON this is often surprisingly difficult. Although various recipes and slurries have been reported in the literature [5], commercial, species-specific enteral for- mulations are likely to become the gold standard for nutritional therapy in the future. In the present case, water rather than 50% dextrose might have proved a more suitable agent to generate the proper consistency, because high loads of simple carbohydrates may be associated with a life-threatening hypokalemia and hypophosphatemia known as refeeding syndrome. Although some initial data suggest that reptiles may be suscepti- ble to refeeding syndrome, it fortunately appears that snakes in particular are resistant to the metabolic changes leading to this problem (because of adaptations to a ‘‘gorge and starve’’ pattern of ingestion). It is still prudent to try to ensure that the food volume does not lead to gastric overload or refeeding syndrome when tube-feeding techniques are employed. Medications recorded in the literature [6] for their use in the treatment of HL include the following: Carnitine plays a role in facilitating lipid metabolism and has been suggested as a potential aid to treatment of hepatopathy in humans. Little clear evidence of positive effect exists in HL patients, but also little risk for adverse effect, so many clinicians add 250 mg/kg of carnitine to the tube-feeding mixture. Choline also facilitates lipid metabolism by promoting the conversion of hepatic fat to phospholipids. Methionine is a precursor amino acid of choline and may itself exert some positive effects. High-quality scientific evidence of positive effect is difficult to obtain, but unused amino acids may be assumed to have little deleterious effect in patients with normal renal function. Forty to 50 mg/kg in the slurry have not been reported to lead to problems in reptiles. Thyroxine (20 mg/kg orally every 48 hours) and anabolic steroids (nan- drolone 0.5–5.0 mg/kg intramuscularly) are sometimes advocated in an attempt to switch the body’s metabolism from catabolism to anab- olism. Their use makes intuitive sense, but once again no evidence clearly supports it. Altering the metabolic state will be a short-term cure if the underlying cause of disease is not also treated and resolved. Lactulose has been suggested as a ‘‘liver-supporting medication’’ in both birds and reptiles. It has two primary roles to play in small animal medicine: (1) as a laxative and (2) as an agent that acidifies colonic contents and thereby lowers blood ammonium levels (and by that mechanism treats hepatic encephalopathy). It may alter the gut micro- environment to lessen the number of bugs that can translocate by means of portal circulation to the liver. This measure conceivably could reduce the chance of secondary bacterial hepatitis. However, the use of this drug may have adverse effects, and it cannot be recommended for incorporation in treatment protocols for HL. HEPATIC LIPIDOSIS IN A BLACK-HEADED PYTHON 597

Silymarin (milk thistle) has a long history of use in the treatment of liver disease, predominantly in controlling inflammation and limiting up- take of toxins. These pathologic pathways are not typical of HL, and beneficial effect is unlikely from the use of this medication. Ursodeoxycholic acid is a bile acid that has beneficial effects on many aspects of hepatic metabolism and is frequently used to treat hepatobili- ary disease in dogs and cats. Because significant differences in bile acid metabolism exist, and several metabolites derived from this bile acid may be toxic, its use in snakes cannot be recommended at this time. Antibiotics would appear to be useful, because many reptiles die from a secondary bacterial hepatitis. The use of antibiotics before a liver biopsy is performed will render any useful information about a bacterial hepatitis difficult to interpret. When the likelihood of bacterial infec- tion complicating the hepatopathy is high, as in the most debilitated snakes with HL, then the most common isolates in secondary or primary bacterial hepatitis are generally sensitive to ceftazidime. In snakes that are very ill at clinical presentation, this drug may be useful during the stabilization phase of treatment. Antinauseates such as metoclopramide may be useful when nausea is pre- venting the resumption of normal eating. In higher vertebrates, the B group vitamins and vitamin C are consumed rapidly in HL-affected animals, so it is prudent to include these in parenteral or oral fluids. These are also anecdotally reported to improve appetite in reptiles. It should be remembered that, in cases of HL in reptiles, exceptionally little scientific evidence exists on which to base specific therapeutic plans, and nutritional therapy is still the backbone of treatment success.

Summary The number of people keeping reptiles in captivity has markedly in- creased, and the generally poor husbandry of these animals will render the diagnosis of HL more frequent. It may become apparent that some species of snakes (especially those of the genus Aspidites and the olive python Liasis olivaceous), and even some of our commonly kept lizards (possibly Pogona spp and Tiliqua spp), have a predisposition to develop HL. In the speciﬁc instance of the genus Aspidites, alterations to the usual husbandry that limit feeding and thereby body weight (both by decreasing frequency and by using small, lean prey) should markedly lessen the chance of the animal’s developing HL. Nonetheless, treating these animals will become a more common occurrence for veterinarians with an interest in reptiles. Hence it is important for clinicians to develop a more aggressive approach to these cases and to build a bank of data with which to promote under- standing of this common malady. All those involved in the medicine and husbandry of these spectacular animals must continually present 598 SIMPSON high-quality information, highlighting HL as a potential outcome of poor husbandry and obesity, so as to reduce its occurrence.

References

[1] Carlton WW, McGavin MD. Thomson’s special veterinary pathology. St. Louis (MO): Mosby; 1995. [2] Bedford GS, Christian KA. Standard metabolic rate and preferred body temperatures in some Australian pythons. Aust J Zool 1998;46:317–28. [3] McCracken HE. Organ location in snakes for diagnostic and surgical evaluation. In: Fowler ME, Miller FE, editors. Zoo and wild animal medicine: current therapy 4. Philadelphia: WB Saunders; 1999. p. 243–8. [4] Divers SJ. Reptilian liver and gastro-intestinal testing. In: Fudge AM, editor. Laboratory medicine: avian and exotic pets. Philadelphia: WB Saunders; 1999. p. 205–9. [5] Donoghue S, Langenburg J. Nutrition. In: Mader DR, editor. Reptile medicine and surgery. Philadelphia: WB Saunders; 1996. p. 149–73. [6] Divers SJ, Cooper JE. Reptile hepatic lipidosis. In: Fudge AM, editor. Seminars in Avian and Exotic Pet Medicine 2000;9:153–64. 本文献由“学霸图书馆-文献云下载”收集自网络，仅供学习交流使用。

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