Reptile & Amphibian Medicine 101
World Small Animal Veterinary Association World Congress Proceedings, 2013
David Vella, BSc, BVSc (Hons), DABVP(Exotic Companion Mammal Practice)
Sydney Exotics & Rabbit Vets, Crows Nest, NSW, Australia

Important Reptilian and Amphibian Traits

Reptiles are often referred to as 'cold-blooded'; however, a more correct term is 'ectothermic.' They have limited ability to create their own body heat, and thus rely on external heat sources to do so. Amphibians are also ectothermic and can become inactive in suboptimal environmental temperatures.

What Species Are Seen In Practice?

The main orders of reptilian species seen in practice include the Squamata (lizards, snakes) and Chelonians (turtles, tortoises). Crocodilians (crocodiles, alligators, etc.) and Sphenodonita (tuataras) are rarely seen in general private practice. The main orders of amphibians seen are Anurans (frogs, toads) and Caudata (salamanders, newts), whilst Gymnophiona (caecilians) are less commonly treated. Reptiles and amphibians collectively are known as 'herpetofauna' or 'herps.'

Bringing the Herp Patient to the Consultation

Appropriate transportation of herps is important in reducing stress and for safety reasons. Instruct owners to bring their pet reptiles secured in cotton type pillow cases and placed into a box. This is sufficient for the majority of pet reptile species (except large tortoises). Snakes are good escape-artists and appropriate transport security is essential. Warmth provision may be required if the transit time is expected to be long or in cold weather. Warmth can be provided by hot water bottles or similar aids. Aquatic turtles should not be transported in water due to risk of aspiration. However, a sample of the water environment should be included for assessment during the consultation.

Amphibians can often be transported in their own enclosure if small enough. Otherwise, utilize small plastic containers or moistened cotton bags. Some species, such as axolotls, should be transported in a plastic container with a small amount of their own tank water. Ensure that amphibians are not subjected to overwarming during any transportation.

The Herp Consultation

History is one of the most important aspects of the herp consultation. A sound knowledge of each species' individual requirements is necessary in order to scrutinize each situation. A thorough investigation of the animal's husbandry, diet and medical history should be explored. The majority of herp maladies can be traced back to inadequate or inappropriate husbandry and feeding. Important aspects to consider are basic enclosure set up, substrates and method of cleaning, ventilation, heating sources and temperatures achieved (in various enclosure zones and at different times of day), relative humidity attained, light/UV sources and cycles, diet and feeding rates, water provision, brumination, and breeding practices. For aquatic species, water quality detail is essential. Information should be gained on the filtration system used and the maintenance of this, also on water changes performed and any water treatments and testing carried out.

Most consultations can be performed with few specialized instruments. A good light source and magnification can become useful as many patients are small in size. A digital weighing scale able to measure to the nearest gram is worthwhile. Oral examination can be aided by the use of oral specula, although the careful use of thin plastic wedges/film and syringe barrels often suffices. In many cases, a fresh faecal exam may be warranted; hence, saline and avian feeding tubes with normal saline may be useful to attain these samples via cloacal flushing.

Handling Herpetofauna

All reptiles should be handled carefully and with gloved hands. Avoid squeezing reptiles and turning them upside down. Amphibians, especially, should only be handled gently and for short periods. Never handle venomous species unless you are trained in this area and familiar with snake-bite first aid.

Snakes

Allow the snake to move over open hands. When restraint is required, gently tighten a hand grip behind the head in the neck region.

Lizards

Many lizards will allow you to pick them up and be supported on open hands. Some lizards require restraint and this can be achieved by placing fingers/hand behind the head in the neck region. Hindlimbs may be held in extension alongside the tail if further immobilization is required, or to facilitate protection from scratching. Some larger lizards may flick their tails and injure the handler; hence, restraint of the tail may also be required.

Chelonians

Depending on the size of the species, many can be picked up and held on a table surface. The limb, neck and tail strength can be remarkably strong making extraction of these body parts for inspection difficult. A firm grip behind the head may be necessary to allow for head examination. In larger chelonians, great care must be taken to avoid being bitten by these powerful animals.

Amphibians

Use powder-free gloves. Dechlorinated or 'aged' water may be used to moisten gloves. Gently nestle the patient with a firm grip around the body. Larger Anurans may benefit from being held around their pelvic girdle with their hindlimbs held in extension.

Examination of Herpetofauna

All herps should be examined in a systematic way. There are several ways to carry this out. A visual examination of the patient may enable assessment of body condition, stance, demeanor, coloration, and respiration for example. Head examination is often carried out last. Begin at the neck and work caudally examining both the condition and texture of the skin/shell and palpating the body and limbs. Coelomic palpation can be carried out readily in most snakes, lizards and anurans, though can be limited in chelonians. Head examination can be aided by ophthalmoscopy and magnification. Ear canals can also be examined in lizards. Oral examination requires opening of the mouth, which can be difficult to achieve in some species. Plastic spatula can be used in snakes and chelonians. Smaller lizards and amphibians may have fragile jaws (especially if affected by metabolic bone disease); thin plastic sheet material is recommended to gently pry the mouth open. In some cases, non-pigmented or small patients can be transilluminated to facilitate internal inspection. Internal cloacal inspection may be tolerated in larger reptiles utilizing otoscopic cones. Auscultation is not often carried out in reptiles. The use of Doppler units may help with cardiac auscultation.

Body weight and body condition should be assessed and scored for every patient. It is necessary to become familiar with what constitutes each species 'normal' body condition. Herp patients are frequently encountered in poor and obese body conditions. Initial body weight measurement of a patient becomes a valuable reference point for future treatment plans. Accurate body weights are also necessary for accurate drug dosing.

Herpetofauna Therapeutics

There are few pharmacokinetic studies that have been performed with herps. Much information on drug use is derived empirically or extrapolated from other species.

There are some important species specifics that need to be considered. Herps have a relatively slower metabolic rate than mammals and hence dosing frequencies are often decreased when compared to mammals. Central to standard therapeutics in herps is the awareness of their ectothermic nature. The provision of a thermal gradient is fundamental to good reptile husbandry practices. A reptile undergoing many forms of 'treatment' should be kept within its preferred body temperature (PBT) range. The provision of PBT will also enhance the reptile's ability to mount an effective immune response. The provision of this temperature range is also thought to enhance the distribution of many administered drugs within the body. Amphibians are tolerant of relatively cooler temperatures when compared to reptiles [usually within an 18-28°C (64-82°F) range]. Other supportive care measures provided should be aimed at enhancing the herp patient's own immune response (e.g., minimize stress, correct handling, appropriate enclosures, correct diet, etc.).

The common routes for medication delivery include subcutaneous, intravenous, intramuscular, intracoelomic, and per os. Other routes can include topical/transdermal, aerosol, intrapneumonic, epicoelomic, intracloacal, and medicated baths.

Fluid Therapy

Fluid therapy serves an important role in herp patients. A key difference between reptiles and amphibians is the presence of semi-permeable skin in amphibians. Illness and skin disorders in amphibians can rapidly alter their fluid and electrolyte balance.

It is safe to assume that many injury and disease states that correlate with dehydration in mammals will also result in similar states in reptiles. Any trauma or disease can lead to a dehydrated state because of pain or shock, or cause a period of inappetence. Reptiles are uricotelic in nature with the majority of their nitrogenous excretory waste product formed as uric acid. In a dehydrated state, the levels of uric acid in a reptile's blood will rise. A dehydrated reptile will gradually lose its ability to function and in chronic cases can lead to such conditions as gout.

Dehydration can sometimes be assessed in reptiles by examination of their skin and eyes. A dehydrated reptile's skin may take on a dull or wrinkled appearance, with 'tenting' of the skin occurring in the more severely dehydrated animals. Their eyes may appear sunken when more severely dehydrated, but can also take on this appearance in a state of emaciation. Some reptiles may also exhibit dry/tacky oral mucosa. Amphibians may exhibit dry or excessively tacky skin, tacky oral mucosa and sunken eyes.

For reptiles, there are several methods available to facilitate rehydration. Perhaps, most easily, they can be provided with water to drink. However, many stressed, injured or ill reptiles may not drink voluntarily. For some animals, placing them into a shallow dish of water (at the patient's temperature) may encourage them to drink and rehydrate. Failure of this method necessitates assisted oral or parenteral hydration therapy.

The exact daily fluid requirement for herps is unclear. A general guideline for maintenance rates in reptiles is to provide 2.5–3.5% of body weight on a daily basis. If the animal is dehydrated, this may be increased to 5% per day. Routes available for rehydrating reptiles include the oral (PO), subcutaneous (SC), intravenous (IV), intraosseous (IO), and intracoelomic (ICe) routes. Amphibians benefit from being able to be provided with topical/transdermal routes of fluid administration initially; however, in more critical patients, SC, IO, and ICe routes may be utilized.

The important points to consider when rehydrating herps

 The animal should be kept in its PBT range to enable normal bodily functions and to enhance the absorption of any fluids provided

 The fluids given must be given at a temperature close to that of the patient and the reptile's PBT range (e.g., 25-35°C)

 If possible, divide the daily fluid requirement over 2 or 3 doses (unless a constant rate infusion is used)

 The rehydration process should be performed slowly and may take several days to achieve

 For smaller animals especially, always start with a body weight of the animal and record this daily during the rehydration process

The recommendation for types of fluids to use in reptiles varies amongst authors. It is recognized that reptiles have a relatively higher intracellular fluid volume when compared to mammals. For this reason, it is suggested to use fluids that are mildly hypotonic to facilitate their intracellular transfusion. The most readily available crystalloids appropriate for use in herps include:

 Ringer's solution (there are various recipes for making amphibian Ringer's)

 Sodium chloride (0.45%) with glucose (2.5%)

 Sodium chloride (0.9%)

It is advised to mix these fluid types and administer as either:

1.  One part Lactated Ringer's solution to two parts sodium chloride (0.45%)/glucose (2.5%) solution (this is the basic preferred solution for use in amphibians), or

2.  Nine parts sodium chloride (0.9%) to one part sterile water for injection.

Drug Therapy

Antimicrobials feature high on the list in herp medicine. Many of the commonly used antibacterials in dog/cat medicine may not be efficacious in herps. Often, higher end antibacterials are required, such as third-generation cephalosporins (e.g., ceftazidime), extended-spectrum penicillins (piperacillin), and aminoglycosides such as amikacin. Other antibacterials utilized include fluoroquinolones, tetracyclines, trimethoprim-sulfonamides, chloramphenicol, azithromycin, and metronidazole.

Anthelmintics are commonly used and can include avermectins (contraindicated in chelonians) and benzimidazoles. Analgesics are important considerations in painful conditions and in surgical procedures. Both opioids (e.g., butorphanol, buprenorphine, morphine) and NSAIDs (e.g., meloxicam, carprofen) are used commonly in herps.

A notable contraindication is the use of avermectins in chelonians. Metronidazole should be used with care in some species due to risk of toxicity.

Herp Clinical Techniques and Diagnostics

Apart from faecal examination for parasitology and microbiology, another important diagnostic tool is blood examination. Blood collection can be challenging in some patients due to size and vessel access. A 'safe' blood collection volume is up to 1% of body weight. Typical blood collection sites include ventral tail vein (snakes, lizards, some caudates), jugular vein (some chelonians, lizards), dorsal tail veins (some chelonians), subcarapacial venous sinus (some chelonians), ventral abdominal vein (some amphibians, lizards). Cardiocentesis is not usually recommended due to risk of pain and iatrogenic cardiac damage, though it can be carried out in snakes and some amphibians.

Other useful diagnostic aids include radiography, ultrasonography and endoscopy.

Basic Reptile Anaesthesia

Reptiles can often be relatively simple, but, at other times, very difficult to reliably anaesthetize. Patient status, size and species influence the type of anaesthesia protocol utilized. It is possible to perform solely injectable anaesthesia, but where possible, gaseous anaesthesia and oxygen supplementation should be provided. Typical premedicants and induction agents can include opioids (morphine, butorphanol), ketamine, benzodiazepines, propofol, and alfaxalone. Gaseous induction via inhalational anesthetics, such as isoflurane, can sometimes be performed; however, reptiles can breath-hold for significant lengths of time. Once induced, many reptiles can be intubated relatively simply using a range of different sized uncuffed endotracheal tubes or modified intravenous catheters. In some instances, some snakes can be intubated whilst in a semi-conscious state and induced to anaesthesia via intermittent positive pressure ventilation.

One of the main issues with anaesthesia in reptiles is that they almost invariably become apneic under anaesthesia. To overcome this, reptiles require ventilation when under anaesthesia. Small mechanical ventilators become useful in this setting. Upon recovery, ventilation is required until consciousness is regained. It is useful to recover reptiles on room air rather than 100% oxygen, as their respiratory drive is governed chiefly by a lack of blood oxygen saturation rather than an increase in blood carbon dioxide levels, as is the case with mammals. A return to breathing or regained righting reflex are good indicators of anaesthesia recovery in most reptiles.

References

References are available on request

  

Speaker Information
(click the speaker's name to view other papers and abstracts submitted by this speaker)

David Vella, BSc, BVSc (Hons), DABVP (Exotic Companion Mammal Practice)
Sydney Exotics & Rabbit Vets
Crows Nest, NSW, Australia


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