ANATOMICAL AND PHYSIOLOGICAL CONSIDERATIONS OF CLINICAL IMPORTANCE OR WHY AREN'T REPTILES MAMMALS?

METABOLIC RATE.The metabolic rates of reptiles are significantly less than those of mammals.This is as a result of the summed effects of several minor differences including :

1 - Lower mitochondrial numbers than endotherms

2 - Reduced membrane areas in mitochondria (both cristae and inner membranes)

3 - Reduced mitochndrial enzyme activity (cytochrome oxidase).

4 - Lower % of visceral mass to total body mass than endotherms.The above give rise to our first important consideration:-

Weight-Related Metabolic Rate.Reptile @ 37C has MR approx 10-20% of mammal same size therefore the pharmacokinetics of drugs will differ from that of mammals. Within reptiles, smaller animals have a faster uptake, distribution and elimination of drugs than larger ones, therefore need increased dose and frequency.

THERMOREGULATION Reptiles are ECTOTHERMS; their metabolic heat production is generally negligable.Their thermal balance is therefore regulated by external heat sources with both behavioural and physilogical mechanisms used to achieve and maintain their Preferred Body Temperature (PBT).There is generally a close correlation between the optimum temperature for a reptile's biochemical and physiological processes, and its preferred PBT. Most diurnal reptiles are HELIOTHERMS and manipulate their body temperature by a variety of means including movement into and out of the sun, adjusting their orientation to the sun, altering their skin colour, peripheral vasoconstriction or dilation, tachycardia (when warming up) or bradycardia (when cooling - reduces the rate of heat loss ). Many nocturnal or secretive reptiles, such as the pythons, are THIGMOTHERMS obtaining their heat by conduction, rather than radiation.Nocturnal, and some diurnal reptiles found in shaded habitats, are THERMOCONFORMERS and do not thermoregulate, their body temperatures following closely that of their environment. In general, reptiles should be provided with a range of temperatures from a relatively cool temperature to a relatively warm thereby allowing the reptile an opportunity to thermoregulate and choose its own PBT. Failure to allow a reptile to achieve its PBT will eventually result in severe physiological disruption including immunosuppression.There are also certain costs associated with thermoregulation, and thermoregulatory precision is compromised if these costs are high eg.if two males of a territorial nature are kept together in a confined space, time spent in intraspecific aggressive encounters may reduce time basking.The lizard Dipsosaurus thermoregulates precisely at a high PBT of 39.1C +/- 2.0 in a low-cost environment, but has a lower PBT and reduced precision of 32.9 +/- 4.0C in a high cost environment. Other clinically important factors relating to body temperature include:

1 - Temperature Related Metabolic Rate. MR doubles with every 10C rise therefore Q10 = 2

2 - Temperature Related pH of Body fluids.This can vary from a pH of 8.3 @ 5C to 7.4 @ 35C.There is no homeostatically set constant pH as such, but a pH target value for any given temperature.

4 - VARIATION IN BODY FLUID COMPOSITION.Plasma protein levels similar to mammals but albumin levels significantly below mammalian therefore may affect degree of protein binding of drugs.

ANATOMICAL CONSIDERATIONS:

1 - RENAL PORTAL SYSTEM - blood from tail, hind legs, cloaca, distal reproductive tract especially hemipenes plus caudal body wall may pass through the kidneys before entering systemic circulation.

2 - HEPATIC PORTAL SYSTEM - blood from GIT and body wall.There is an anastomosis between Renal Portal & Hepatic Portal Systems. Therefore any drugs injected into caudal body may arrive at kidneys at potentially nephrotoxic levels. V.important with aminoglycosides eg.gentamicin.

NITROGEN EXCRETION Mostly uric acid (uricotelic) but variations according to environmental adaptation

Reptiles lack Loop of Henle therefore unable to produce hyperosmotic urine.- can't concentrate it therefore to avoid Xs water loss they excrete uric acid which is only sparingly soluble and can be excreted at high concentration with minimal water loss as a sludge or paste. Excess mineral load excreted by salt glands eg.in nostrils of iguanas excess Na, K, HCO3 and Cl is excreted.In the saltwater crocodile C.porosus there are numerous lingual glands.Uricotely is important because impairment of fluid balance or renal disease eg gentamicin induced nephrotoxicity --->crystallization of uric acid crystals ---> visceral or articular gout.

PRINCIPLES OF ANTIBIOTIC THERAPY One of the commonest reptile pathogen is pseudomonas therefore until recently the aminoglycosides have ben extensively used in reptile medications. Therefore consider:

Glomerular Filtration Rate - Reduced MR compared to mammals produces a reduced GFR Important for eg aminogloycosides which are excreted selectively by kidneys, because reduced GFR -- reduced renal clearence -->increased risk of toxicity of mammalian dosage regime if initiated.

ENVIRONMENTAL TEMPERATURE Inc temp --> inc MR --> inc GFR ---> reduced dwell time.Also with gentamicin, inc temp --> increased tissue binding --> inc nephrotoxicity. Remember interspecific variations - reptiles are not a homogenous group and a green lizard (Lacerta viridis) is no closer related to an iguana (Iguana iguana) than a cat is to a horse!. Therefore all reptiles undergoing antibiotic therapy (& other drugs) should be at their preferred body temperature, unless otherwise stated eg gentamicin less toxic @ lower temperatures. Also aminoglycosides particularly contraindicated in renal dysfunction; if used maintain fluid therapy (up to 4% bodyweight per day) plus plus fasting to reduce uric acid production.

PRINCIPLES OF ANAESTHESIA OF REPTILES

Anatomical Considerations

1 - Lung structure. Chelonia - lungs occupy dorsal section of shell & are adhered to overlying dermal bones of carapace. rigid carapacal wall.No functional diaphragm.Respiration achieved by movement of muscle groups esp legs and pelvicum attrahans thereby altering volume in shell. Closure of glottis imposes respiratory cycle. Diving terrapins able to constrict lungs down via smooth muscle (well innervated) ---> inc pulmonary circulatory pressure --> shunting.

Lizards - Paired lungs; often have air sacs.No true diaphragm.

Snakes.Anterior faveolar region plus posterior (relatively avascular) air sac --- cloacal area.Glottis closes therefore air shuttles backwards and forwards.

2 - In Snakes, lizards & chelonia - 3 chambered heart --- right to left shunts therefore bypasses lungs.

3 - Tolerance to anoxia.Can tolerate high lactic acid levels Variable oxygen affinities plus Bohr effect.Therefore probs masking down esp chelonia, therefore best to give induction agent. Ketamine and Saffan OK im but long recovery time therefore induction agent of choice is Rapinvet but must be given iv. Maintain with isofluorane - less than 1% metabolised.

1- Maintain @ PBT before & after anaesthetic

2 -Most reptiles cease to breathe during anaesthesia therefore adopt Intermittant Positive Pressue Ventillation.CO2 receptors in respiratory tract therefore on recovery often helps to ventilate by mouth cos CO2 has a moderate to major stimulatory effect in many lizards, snakes and chelonia (Xs --> depressive effect).

4 - Monitoring can be problematic

- Reflexes

- Jugular pulse

- Heart rate - doppler or ultrasound

- oesophageal steth

- ECG?

5 - Respiratory stimulants eg Dopram V

6 - Neuromuscular blockade esp gentamicin.

DISEASES OF REPTILES

CHELONIA This group covers the tortoises, box tortoises and terrapins.Box tortoises require totally different husbandry from the more usual Mediterranean species, requiring a higher humidity,higher temperatures, access to bathing facilities and a more carnivorous diet. Body condition in chelonia can be difficult to assess because of their shells.For this reason much effort has gone into researching the relationship of mass to length to provide useful indices.This lead to the formulation of graphs depicting the mean and "dangerously low" mass to length curves for the Spur-thighed tortoise Testudo graeca and Herman's tortoise Testudo hermanii.These ratios can vary depending upon the tortoise's age, sex and stage of reproductive activity (an average egg weighs around 28g), but are still a valuable adjunct to a thorough clinical examination.

Viral Diseases

Viral Disease of Mediterranean Tortoises.Previously known as Runny Nose Syndrome (RNS).Virus is probably a herpesvirus as diagnosed by demonstration of intracytoplasmic viral inclusions in hepatocytes.Clinical picture is of persistant rhinitis varying from a watery serous to a thick mucoiddischarge, often accompanied by recurring parasitism (especially with flagellates) and a non-dietary related hypovitaminosis A.Appetite remains good but diarrhoea is often a feature.This disease is untreatable as there appears to be an accompanying immunosuppression. Eventually anaemia, jaundicing ensue leading eventually to death often as a result of a secondary stomatitis, pneumonia or renal failure. The species Testudo ibera appears to be an asymptommatic carrier, with deaths in mixed collections being mostly confined to the North African Spur-thighed tortoise Testudo g.graeca.To differentiate between the two species (originally considered subspecies of Testudo graeca) look at the first vertebral scute - in T.g.graeca it has rounded edges, whereas in T.ibera the edges are markedly squared off.

Bacterial Diseases

Abcesses are very common in chelonia.Reptilian pus is rarely liquid but is more often thick, caseous material.A thick fibrous capsule usually surrounds the abcess making antibiotic penetration difficult, so surgery is often resorted to to effect a cure.Where limbs, joints or extremities such as the rostral nares are affected, then radiography should be performed to check for osteolysis in the underlying bone.Ear abcesses are common, and present as bulging of the tympanic membrane on one or both sides.These are often the sequelae to a bacterial stomatitis, with infection ascending the eustachian tube into the middle ear cavity. Management of all abcesses is similar, involving the combination of appropriate systemic antibiosis plus the surgical removal of caseous material and debridement followed by irrigation with topical antibiotics or povidone-iodine. Stomatitis (or mouth rot) is occasionally encountered especially following hibernation. There may be ulcerative, haemorhagic lesions or whitish plaques on the tongue, fauces and hard palate.Bacterial infections usually play a significant role, although viral and fungal aetiologies have been implicated. Following swabbing for routine culture and sensitivity testing, debridement under a general anaesthetic is recommended. Systemic and topical antibiotics should be used - if fungi are implicated then try clotrimazole (Canestan)topically. Importantly one should instigate supportive measures including stomach tubing with fluids such as glucose/electrolyte mixes. Chelonia with stomatits will not eat or drink voluntarily. Septicaemia presents as ecchymotic haemorrhages in the skin and in the shell.In severe cases fluid may accumulate beneath the keratin shields of the shell.Jaundicing may be seen.Treat with systemic antibiotics. Much fuss is made about asymptomatic Salmonella infections, especially in terrapins, primarily hatchling red-eared sliders (Trachemys scripa). Zoonotic episodes involving Salmonellae from chelonia are relatively rare and are usually due to a breakdown in hygiene and poor husbandry, allowing an environmental build up.

Parasites

Flagellate infestations can be associated with gastro-intestinal disease and inappetance in chelonia, which may be seen to void large quantities of watery diarrhoea.Light microscopy will reveal huge numbers of these motile protozoa.Considered normal inhabitants of the gut fauna, in large numbers they are pathogenic - in many cases they are secondary opportunists so the possibility of concurrent disease should be considered.Treat with metronidazole delivered by stomach tube @ 100-275mg/kg once only. Occasionally Hexamita may be a cause of nephritis.Treatment is with dimetridazole @ 40mg/kg orally daily for 5 days. It seems that 30-40% of tortoises carry nematode infestations, usually Sulcascaris and Angusticaecum.Large infestations will compete for the host's nutrition, and can cause blockages.Larval stages undergo visceral migration and can cause pathology in a variety of organ systems.Life cycles are believed to be indirect though they have not been elucidated - Augusticaecum can have a direct life cycle.Regular worming with Fenbendazole @ 100mg/kg twice yearly is to be recommended - during pre- and post-hibernation checks.Some authorities recommend using oxfendazole but as fenbendazole is metabolised to oxfendazole it is probably largely academic.

PRINCIPLES OF HIBERNATION

Triggered by - reduced ambient temps

- reduced photoperiod

- reduced light intensity

Reversed by - increased temp (no light in box) NB low temperature adaptation.Utilise fat and liver glycogen reserves over winter -- lose 0.2-0.4g/day - expect to loose around 1% body weight per month. Water is lost via respiration therefore PCV rises. Urea levels rise - > Inc osmolality of blood --> progressive reduction in kidney function --> anuria

ii) suppression of WBC therefore immunosuppression --> 2ry infections eg stomatitis.

At re-emergence - massive rise in blood glucose from liver glycogen stores to fuel initial foraging

- must drink within 10 days -> reduction in blood urea levels and PCV

- must eat within 3 - 4 weeks

If insufficient fat reserves --> break down muscle to release AAs, but protein catabolism --> Xs urea therefore worsens condition. Defy in fat soluble vits. Therefore

- correct dehydration

- give vitamins

- temp around 30C

- give easily assimilated diet

Probably best considered as a syndrome, Mediterranean tortoises awakening from hibernation occasionally will refuse to feed. Typically this is due to inadequate preparation the previous autumn with inadequate deposition of fat in the fat body.The tortoise utilises its entire fat reserves, thereby also exhausting its fat soluble vitamins and is forced to breakdown muscle and other tissues as a protein source to provide an alternative energy and amino acid source. Other obvious causes include stomatitis,septicaemia resulting from a bacteraemia during hibernation while the tortoise immune system is compromised, blindness secondary to cataract formation as a result of exposure to excessively low temperatures during hibernation.Treatment can be prolonged, and involves maintaining fluid balance by stomach tubing with oral rehydration preparations at around 4% bodyweight per day.An easily assimilated food such as Reanimyl (Virbac) can be given twice weekly. Any specific disease conditions, such as stomatitis, should be addressed.

Egg-Binding

Any female chelonian presented with non-specific signs of ill health, or persistant straining should be assessed for dystocia, or egg-binding.There are two types of egg-binding:

1 - Pre-ovulatory (Follicular stasis).The ovaries become overloaded with retained yolks, developing into large pendulous masses which act as space occupying lesions. Diagnosis should be attempted by rigid endoscopy introduced at the inguinal fossa or ultrasound, again directed at the inguinal fossa.

2 - Post-ovulatory.Eggs which are shelled to varying degrees are present within the oviduct.Radiography is diagnostic.

Treatment of post-ovulatory dystocia should be attempted by first of all priming the reproductive tract over five days with parenteral calcium @ 500mg/kg of 10% calcium solution,followed on the fifth day by oxytocin @ 1.0iu/kg. If this is unsuccessful after a couple of trials then removal via a surgical flap created in the plastron is advised, possibly accompanied by salpingectomy with or without an ovariectomy. The dystocia may prove to be secondary to a wide variety of factors including environmental (no provision for egg deposition sites), hypocalcaemia, intracoelomic tumours and so on.

Nutrition

Hypovitaminosis A is occasionally encountered especially in young red-eared sliders.Affected chelonia show a variety of ocular lesions including swollen eyelids due to squamous metaplasia of the orbital glands and their ducts.Awhitish cellular mass may develop behind the lower lid. Squamous metaplasia also affects the renal tubules, causing kidney damage.Affected chelonia are often anorexic as they cannot see to locate food.Treatment is with vitamin A given i.m.@ 1 000 - 5 000 iu weekly for 4 weeks, and the addition of dietry vitamin A supplements.

Shell abnormalities can arise from dietary imbalances especiallyin young herbivorous chelonia.Abnormalities in the calcium:phosphorus ratio (should be around 2:1) or too high a protein intake resulting in too rapid a growth rate can lead to an obvious doming of the carapacial scutes.

SNAKES

Bacterial Infections.

Bacterial infections are relatively common in captive snakes, and those bacteria isolated are usually environmental contaminants such as Pseudomonas and Aeromonas but other bacteria such as Pasteurella are occasionally encountered.As with most reptilian bacterial disease entities, there is often an underlying cause such as poor husbandry, stress leading to immunosuppression, parasitism especially external mites.A common presentation is that of ventral dermal necrosis, which has the appearance of blisters and sores on the ventral scales. Usually associated with too damp an environment - in semi-aquatic species it can be initiated by the dermal penetration of hookworm larvae (Kalicephalus - treat with fenbendazole @ 25mg/kg weekly for at least two to three weeks). If left untreated it may progress to a septicaemia.Treatment is with topical povidone-iodine plus appropriate systemic antibiosis - successful antibiotics include enrofloxacin @ 10mg/kg every other day, gentimicin @ 10mg im or 2.5mg/kg s.c.or tobramycin @ 10 mg/kg i.m.e.o.d. Parenteral vitamin A @ 1 000 to 5000iu will induce ecdysis (skin sloughing) helping to remove much of the infected skin and necrotic material. Any abnormal swelling should be investigated as a potential abcess and may require surgery plus systemic antibiosis. Stomatitis usually has a bacterial aetiology although there may be fungal involvement.This can present as inflammation of the oral and pharyngeal membranes progressing to ulcerative lesions involving the palatine area, the trachea and the tongue sheath. A diphtheritic membrane may be present.Occasionally infection may track up the lachrymal duct resulting in a subspectacular abcess over one or both corneas.Management should begin with surgical debridement of necrotic tissue followed by systemic and topical antibiotics plus topical povidone-iodine daily.A subspectacular abcess may need surgical intervention to remove the inspissated pus and flush through the nasolachrymal duct. Snakes will not feed whilst suffering from stomatitis so fluid such as Hartman's @ 15-25ml/kg and nutritional support should be given by stomach tube during this time.The stomach tube should be lubricated and coated with appropriate antibiotic to try to prevent iatrogenic spread of infection to the oesophagus and further. Septicaemic snakes present as inappetant with petechial haemorrhages visable in the skin, especially the ventral scales.The snake may show central nervous signs such as incoordination, frantic movements or loss of the righting reflex.

Burns. In captivity some snakes can show thigmothermy whereby they will crawl on to a warm surface as a means of achieving their prefered body temperature.Unfortunately if this is a powerful ceramic heater then localised burning of the dermis may occur. Debride necrotic material and treat with topical povidine-iodine. Antibiotic or antifungal medication may be required to prevent secondary infection (Panolog cream).If the burns are extensive then fluid therapy with Hartman's @ 15-25ml/kg daily should be instigated.Scaring will eventually result which may lead to localised areas of dysecdysis; if scarring is extensive then constricting snakes may be unable to constrict which may prevent then from initiating their feeding behaviour sequence.

Dysecdysis.

Ecdysis, or skin shedding/sloughing is a normal aspect of growth in snakes and most other reptiles and is controlled in part by the endocrine system.The skin is usually cast whole, starting from the rostrum and the snake crawls out of it, inverting the skin as it does so. Dysecdysis usually involves the retention of all or part of the sloughed skin and is commonly an environmental deficiency such as inadequate humidity, lack of provision of structures such as branches on which the snake can rub itself to initiate shedding, or as a result of scarring. Endocrinological disorders may also be the cause.Treatment usually involves regular bathing in warm water followed by the gentle removal of retained patches, or placing the snake in a damp towel, whereby the snake can rub the loose patches off.If the spectacle over the cornea is retained, then gentle rubbing whilst applying slight pressure with a damp cotton bud should eventually cause some rucking of the spectacle and allow its removal.DO NOT PULL WITH TWEEZERS OR FORCEPS as you risk avulsing the cornea with consequent loss of the use of that eye.

Internal Parasites.

Cryptosporidia.This is a protozoan infection of both snakes and lizards.The life cycle is direct and reptiles become infected by exposure to water containing infective oocysts.The original source may be asymptomatically infected rodent prey.Classic signs are chronic regurgitation, extreme weight loss, depression, mucus-laden stools and an obvious abdominal bulge caused by hypertrophy of the stomach lining.There is no recognised effective treatment and because of its zoonotic nature euthanasia is usually recommended.

Entomaeba.Highly pathogenic, ingestion of faecally contaminated water or food with the infective cysts leads to the establishment of an infection evidenced as dysentry(mucus-laden, bile stained and/or showing frank blood), anorexia, dehydration, wasting and death. Metronidazole @ 100-275mg/kg is the drug of choice. Potentially zoonotic.

External Parasites

Snake mites (Ophionyssus natracis) can build up to seriously large numbers in viviaria.They are blood feeders and tend to accumulate on those areas of the body which offer the most protection - under the scales, the postorbital area, labial pits and any skin folds around the mouth or cloaca.Apart from irritation, large numbers can be associated with anaemia,dysecdysis, depression and anorexia. Reproduction occurs readily in the vivarium, so treatment must include the thorough cleansing of all affected vivaria.What cannot be sterilised with a mild bleach solution (5mls per gallon) must be disposed of.Replace usual substrate with paper (changed daily).Snakes can be repeatedly washed with warm water to physically remove any mites.Injecting ivermection @ 200ug/kg s.c.(NB:toxic to chelonia) every two weeks will kill those that feed on the snake.An alternative regime is to use the insecticide impregnated strips Vapona. Strips of Vapona(6mm per 10 cubic feet) are placed into a jar with holes punched in the lid to prevent the snake coming into contact with the strip, and this is placed into the vivarium for two to three hours two or three times weekly for two to three weeks.The water dish is removed during the hours of treatment. Ticks may occasionally also be encountered. They are best removed individually by grasping them with forceps, turning them on to their backs and whilst applying a constant pressure gently but firmly pulling,.Treat any resulting wound or granuloma with topical povidine-iodine; if the infestation is extensive thenbroad spectrum systemic antibiotics should be given as a preventative measure.

Central Nervous Signs

Snakes can show signs of central nervous system (CNS) dysfunction in a variety of ways such as loss of the righting reflex, aberrant behaviour, and "star gazing". Important differential diagnoses are:

1 - Septicaemia

2 - Thiamine (vitamin B1) deficiency.Fish-eating snakes such as the garter snakes (Thamnophis species) are often fed on marine fish obtained from the fishmongers, such as whitebait. This contains high levels of the enzyme thiaminase which destroys the snakes endogenous thiamine resulting in cerebro-cortical necrosis.Treatment is with B1 supplementation, and is avoided by providing a B1 supplement plus boiling of fish before feeding to denature the thiaminase.

3 - Protozoa.Acanthomoeba and Toxoplasma have been isolated as the cause CNS disturbances.Suggested treatments include metronidazole @ 100-275mg/kg p.o.once only (only 40mg/kg for King snakes and Indigo snakes) or trimethoprim/sulphadiazine @ 15mg/kg p.o.daily.Treatment not always successful.These are both potential zoonoses.

4 - Organophosphates such as insecticide aerosols.Over-exposure to Vapona is occasionally seen.Treat with atropine @ 0.04mg/kg.i.m.

5 - IBDB especially pythons.Regurgitation seen in boaes, but CNS in Pythonidae.- C-type Retrovirus.

LIZARDS

Bacterial Diseases

These present in much the same way as with other reptiles, where in septicaemic cases one sees anorexia, lethargy, and petechial haemorrhages in the skin. Any abnormal lumps or asymmetry of outline should be assessed for the possibility of it being an abcess. Treatment as for other species.Bacterial pneumonia can be particularly common in Asian Water Dragons (Hydrosaurus sp) and presents as a very marked dyspneaand gaping.There may be a tracheal exudate and this should be examined for worm eggs or larvae to differentiate from a lungworm (Entomelas) infestation. Systemic antibiotics are required for a bacterial pneumonia, whereas fenbendazole @ 40-50mg/kg every two weeks for two to three treatments.

Parasites.

Endoparasites such as flagellates and worms (such as Oswalsocruzia, Camallanus and Oxyurus sp.) are occasionally encountered.Treat as in other reptiles.

Ectoparasites include ticks and mites (Hirstiella trombidiiformis) and these should be dealt with as outlined with snakes.

Trauma

Many species of lizard show autotomy, whereby if the tail is grasped it will come away at a predetermined weak spot.The tail continues to wriggle, presumably distracting a potential predator while the lizard escapes.Should this happen then treat the tail stump with povidine-iodene topically.Eventually a new tail will develop although it often differs in dimension and colour from the original.Occasionally a double tail may grow.

Dystocia

Egg binding as discussed with chelonia can also been seen in lizards, especially adult female iguanas.Treatment regime is the same, which if unsuccessful should be followed up by surgical removal of the eggs ("caesarian") which may or may not involve a salpingectomy and/or ovariectomy.

Nutritional Disorders

Hypervitaminosis D can occur through over zealous use of vitaminD3 supplements. Signs include soft tissue mineralization especially of the arterial walls, the respiratory system, gastro-intestinal system and the urinogenital organs.These are visible radiographically and one may also see periosteal proliferation.

Bone Diseases

Bone diseases are very common in lizards, and any swelling, fracture or paralysis should be considered as a possible sign of a bone disorder.Diagnostic procedures should include radiography and where feasable, a blood sample to assess serum calcium and phosphorus levels.Aetiologies include: dietary calcium deficiency, dietary calcium/phosphorus imbalance, dietary vitamin D3deficiency, lack of exposure to ultra violet light, dietary protein deficiency, liver, kidney and intestinal disease.However most skeletal problems are dietary linked and are often lumped together under the title Nutritional Osteodystrophy, the clinical manifestations of which can be due to a variety of related diseasesyndromes.

1 - Osteoporosis.Seen with protein deficient diets, prolonged corticosteroid treatment, lack of bone use and senile changes, this disease involves the reabsorption of osteoid faster than new protein is deposited leading to brittle bones and consequent often multiple fractures.

2 -Osteomalacia.Seen in adults only there is insufficient mineralization of the bones causing bending and fractures as well as folding fractures to occur. There is often increased osteoid deposition at tendon insertions and bone curvatures.

3 - Rickets.Seen in young reptiles, the aetiology is very similar to osteomalacia although the radiographic appearance differs slightly, with the formation of widened radiolucent epiphyseal plates.

4 - Osteodystrophy fibrosa.Chronic mineral imbalance or osteoporosis can lead to this, where osteoid is absorbed and replaced by connective tissue.Affected bones are larger than normal and soft.The mandibles in particular can be gently compressed hence the term "rubber jaw".

5 - Nutritional Secondary Hyperparathyroidism.Prolonged hypocalcaemia will cause an excessive production of parathyroid hormone which initiates the resorption of calcium from the bone matrix to try to maintain normal serum calcium levels.This results in osteomalacia (adults) or rickets (young).

Lizards such as iguanas with low serum calcium levels can show a hypocalcemic tetany, often first showing as a twitching of the toes. In extreme cases this can progress to general muscleweakness and eventual complete flaccidity. Treat with I.V calcium @500mg/kg of 10% calcium solution.Prevention is with regular calcium and vitamin D3 supplementation with proprietary products.

AMPHIBIANS

Amphibians may not seem to appeal as pets, yet there are many devoted keepers. Possibly the commonest ones kept are Axolotyls, African Clawed Toads (Xenopus laevis) and North American Bullfrogs which were imported in large numbers as tadpoles for the water gardening trade.

Divided into three orders - the wormlike Caecilians, the tailed Caudata or Urodeles (newts and salamanders) and the tailess Anurans (frogs and toads). Obvious signs of disease include listlessness, loss of appetite, abnormal posture, loss of the righting reflex and alterations in skin colourationor obvious skin lesions.Loss of body symmetry can be due to cysts and tumours.

Bacterial Diseases

As in fish, most of the bacteria encountered in amphibian disease are opportunist environmental contaminants, typically aeromonas or pseudomonas.Aeromonas infections are the cause of Red Leg seen in Anurans, where there is a very characteristic erythema of the ventral and medial surfaces of the legs, and on the belly. In other cases ulcerations and granulomas may be seen. Swabbing for laboratory culture and antibiotic sensitivity should be undergone, although a good initial antibiotic to use is enrofloxacin either by injection @ 5-10mg/kg e.o.d or as a bath (30ppm. for up to 5 hours maximum on alternate days) until results are available. Severe ulcerations and granulomas should be cleaned with povidone-iodine daily if necessary, although this will slow down the re-epitheliarisation of dermal ulcerations. Mycobacterial infections are seen, which often present as nodules in the skin, and granulomas in the viscera although as in fish, signs vary depending upon which organs are affected. Usually accompanied by a chronic debilitation. Diagnosis usually either by demonstrating acid-fast organisms using a Ziehl-Nieelson staining of a direct smear, or histopathology.Euthanasia usually recommended as antibiotic treatment rarely effective, and can be zoonotic gaining access via cuts and abrasions, where granulomas develop and from where it can occasionally spread along the lymphatics. Rarely become systemic as usually only able to survive at the relatively low temperatures encountered at the extremities and the outer skin layers.

Fungal Diseases

May be seen on aquatic amphibians, often as a result of secondary infection. Saprolegnia appears as a cotton wool-like lesion, whereas other fungal infections, especially if sytemic, may present as granulomata.Treat external infections with topical povidone-iodine daily.

Parasites.

Many internal and external parasites of amphibia have been described.Probably one of the most significant is the protozoal ectoparasite of aquatic amphibians and of the aquatic stages of terrestrial forms is Oodinium pillularis. Irritant in large numbers affected amphibia develop a greyish covering due to excessive mucus production over the skin and gills.The gills are particularly targeted and if severe then respiration is impaired. Affected individuals become debilitated and may die.Treat with metronidazole at 10-14mg/l.

Nutritional Disorders

Hypocalcaemia- this can be actual, or relative if there is a hyperphoshataemia, or as a result of hypovitaminosis D3.Amphibia fed an unsupplemented diet of meat, heart or insects (usually crickets) can suffer from a deficiency of dietary calcium.Affected individuals can show scoliosis, folding or pathological fractures and paralysis.Diagnosis requires radiography to assess bone density.Easily prevented by using one of the readily available calcium/vitamin D3 supplements available.

The larger bullfrogs are usually fed on a diet of mice, which can give an excessive protein intake.Affected frogs can show swelling of the digits due to an accumulation of urate crystals in the joints - the tophi characteristic of gout.Urates can be deposited in or around other organs and the sugns seen may reflect this.Surgical removal of tophi can be attempted, plus allopurinol at 10mg/kg p.o every other day to prevent further urate deposition.