Lizard (Saurian) Medicine

Greg Lewbart M.S., V.M.D., Dipl. ACZM
greg_lewbart@ncsu.edu

I.  Introduction  

There are over 3700 species of lizards worldwide. The suborder Sauria belongs in the order Squamata which contains both the snakes and the lizards. There are 16 recognized families of lizards containing over 380 different genera. Lizards occur on every continent except Antarctica (surprise) and occupy both island and mainland habitats. The majority of species are centered in the tropical and sub-tropical regions of the world. Lizards may be as small as 1.5 cm in length or as long as 3 meters. Most are in the 20-30 cm range.

II.  Anatomy and Physiology

The following facts are important but it should be pointed out that these are generalizations and exceptions exist.

1.  Most lizards have well developed tongues.

2.  Most lizards have external ear openings and eyelids which can be closed.

3.  Nearly all species have teeth which can be replaced.

4.  Some species possess a parietal eye also known as the "third eye." This structure is located at the top of the head and is usually covered by a thin opaque scale. The "eye" connects directly via nervous tissue to the pineal body in the brain. Researchers believe this structure functions in regulating the biological clock via changing photoperiods. Do not mistake this structure for a lesion!

5.  Lizards have two well developed lungs and lack a true diaphragm.

6.  The heart, like in most reptiles, has three chambers (2 atria and one ventricle). There is a partial ventricular septum but very little mixing of oxygenated and unoxygenated blood.

7.  Fertilization is internal in the oviduct which is usually paired. Male lizards have two separate reproductive tracts (the paired testes have their own copulatory organs called hemipenes). A male lizard may exhaust its supply of sperm from one teste and then switch hemipene to utilize the other teste. In a few species the females can store sperm and some species of lizards are actually parthenogenetic (all of the animals are females and young develop from unfertilized eggs). This occurs in some species of whiptails, geckos and rock lizards (who says males are necessary?)

8.  Lizards have paired kidneys. A common cloacal opening is utilized by the urogenital and gastrointestinal tracts.

9.  The gastrointestinal tract is a fairly standard vertebrate model. A large oral cavity (the glottis is located directly behind the tongue) leads to an esophagus which opens into an S-shaped stomach. A gall bladder is always present and the liver, spleen and pancreas are well developed.

10.  Certain species of lizards can voluntarily shed their tail as a defense mechanism (skinks and geckos). A new tail can be grown but is rarely as nice as the original.

III.  Anesthesia/Restraint

1.  Simple procedures such as blood sampling, radiography and general physical examination can be performed without anesthesia in most lizards. A pair of thick gloves may help protect the handler from superficial bites and scratches.

2.  Invasive procedures like abdominal surgery, orthopaedic surgery and surgical biopsy will require general anesthesia. A number of anesthetics are reported in the literature for use in lizards. Both injectable and inhalant anesthetic agents have been used. One standard approach at the CVM is to induce lizards (specifically iguanas) with 15 mg/kg IM ketamine (given in a front limb) and then place them on inhalant isoflurane. If the lizard is not too fractious it may simply be masked down with isoflurane and then intubated without the use of ketamine. Some clinicians choose to use ketamine alone and a dose of 30-60 mg/kg may be required. Medetomidine in combination with a lower ketamine dose and then reversal with atipamezole is currently being investigated and shows some promise, although medetomidine appears ineffective in iguanas. Lizards are easy to intubate since the highly visible glottis is located at the base of the tongue. Most lizards will be too small for standard mammalian endotracheal tubes so the clinician will have to improvise with a red rubber catheter or tom cat catheter. The tube can be tied in with gauze. Detecting a pulse during anesthesia can be difficult. The heart is located far cranially and can be auscultated almost directly between the base of the forelimbs. During surgery, when the animal is in dorsal recumbency, the pulse can be monitored quite effectively with a contact Doppler device. A well placed esophageal stethoscope can also detect the cardiac pulse.

3.  Hydration, as in mammals, is also important for lizards. Dehydrated patients must be rehydrated before anesthesia. This can be done by giving subcutaneous lactated ringers, physiological saline, or a 1:2 dilution of the two respectively. A maintenance guideline to follow for lizards is 15-25 ml/kg/day. The more ambitious clinician may try to place an IV catheter. This is best done in the ventral caudal vein but is difficult in most lizards. During abdominal surgery, a small catheter can be placed in the large mid-ventral abdominal vein of the iguana.

VI.  Blood Collection and Hematology

1.  The most practical site for blood collection in lizards is in the tail. Most workers like to use the ventral caudal vein which is located just ventral to the vertebral bodies of the tail. A needle is placed between the scales and perpendicular to the tail until it meets resistance from bone. Negative pressure is applied and the needle is slowly withdrawn until blood is seen in the hub (think of bleeding a cow from the tail vein). Others prefer bleeding from the dorsal spinal vessels which are located above the vertebral bodies on the dorsal aspect of the animal. This site has the advantage of not needing to turn the animal on its back. Again, the needle is inserted at a near 90 degree angle until resistance is felt and then negative pressure is applied with the syringe. Most workers recommend using a heparinized syringe and needle since the blood clots rapidly. Lithium heparin works well. Never place reptile blood in an EDTA tube as the sample frequently hemolyzes! It is reasonable to withdraw a sample equivalent to 0.5% of the animal's total body weight (5 cc from a 1 kg iguana) but 2-3 cc will usually be adequate for a CBC and chemistry panel. Many reptile medicine references contain reference range values for some lizard species (see reference list).

VII. Non-Infectious Diseases

1.  Thermal burns. These injuries are all too common and usually result from the improper use of either a hot rock or light bulb. Reptiles are generally attracted to heat but sometimes do not realize when they are sustaining an injury. Severe wounds may require antibiotic and fluid therapy. Superficial wounds can be managed with a topical antibiotic ointment such as Silvadene Cream.

2.  Impaction. Certain species of lizards including iguanas have a narrow passage between the colon and the rectum. Certain cage substrate materials like sand, gravel, corn cob or even hay may become lodged in the gastrointestinal tract if these items are consumed. Radiographs may be needed for an accurate diagnosis and surgery may be warranted in severe cases. If abdominal (coelomic) surgery is to be performed, a ventral paramedian incision is recommended since some lizards (iguanas) have a large mid-ventral vein (some surgeons use the mid-ventral incision site without complication). Enterotomy and closures can be performed as in mammals. The peritoneum is extremely thin and is usually not closed separately. Skin sutures should stay in for a minimum of 4-6 weeks.

3.  Egg Retention (Dystocia). Female iguanas and perhaps other species of lizards will frequently produce infertile eggs in captivity but not lay them. The owner will usually notice abdominal distension coinciding with a decrease in appetite. This usually occurs between February and April in green iguanas. Radiographs will confirm the presence of eggs. A green iguana may lay between 10 and 70 eggs although the norm is closer to 25. Animals with retained eggs will start to appear emaciated and lethargic. Egg retention probably has several causes, nearly all of which relate to shortcomings in captivity. Iguanas in the wild lay eggs in elaborate burrows which are difficult to simulate in captivity. Nutritional problems or other diseases may predispose a lizard to egg retention (also called egg-binding). Once the animal has stopped eating completely and has lost a significant amount of muscle mass (these animals may not lose much weight since the developing eggs weigh a lot) surgery is in order. Some clinicians like to perform an ovario-hysterectomy in these instances while others may find it easier to perform a hysterotomy/salpingotomy and remove the eggs one at a time. There are two branches or horns of the uterus (also termed the oviduct) and both usually contain eggs. If the ovaries and uterus are to be removed, care must be taken to avoid the adrenals and to be aware of the vena cava which is in close proximity to the ovaries. As with any coelomic cavity surgery in lizards, care must be taken to avoid the large mid ventral vein. However, this vein is not usually adhered to the body wall so a careful mid-ventral incision should be satisfactory. The bladder can also be quite large and is located in the caudal ventral abdomen. Many iguanas also have a very large abdominal fat pad. DeNardo et al. thoroughly discuss this topic and treatment options in a recent publication (see reference section).

  Some clinicians have reported success using oxytocin to aid in resolving egg retention. I have seen this work one time, but still, all of the eggs were not voided and the animal went to surgery. An empirical dose would be 3.0 IU/kg oxytocin IM. One risk with this treatment would be the chance that the oviduct could rupture and dump the eggs into the coelom.

4.  Metabolic Bone Disease. This is probably the number one disease of captive green iguanas although it is not common in other species of (carnivorous) lizards. Metabolic Bone Disease (sometimes referred to as MBD) actually has a complex of causes, all of which result in demineralization of bone. The causes include insufficient calcium in the diet, too much phosphorus in the diet, a lack of vitamin D, and more rarely a primary endocrine imbalance involving the thyroid or parathyroid glands. What actually happens is termed nutritional secondary hyperparathyroidism, in which the body mobilizes calcium from bone for other bodily functions.

Animals will present with a history of lameness, anorexia or depression. Some animals will have an enlarged rubber-like mandible while others will have limbs which appear large and swollen. These signs represent the condition of severe osteodystrophy. Radiographs will reveal thin bone cortices and commonly pathological fractures or evidence of recently or partially healed fractures.

Treatment involves educating the client and supplementing the iguana's diet with calcium, vitamin D, ultraviolet light (preferably natural sunlight). I have seen animals that have been on very well balanced vegetarian diets with vitamin supplementation present with MBD. In order to remain healthy, green iguanas seem to some require some exposure to natural sunlight. Ideally, owners should allow their animals to remain outside for several hours each week in a protected and secure area which also provided some shade. Iguanas should not be left outside if temperatures drop below 70 degrees F. There are several ways to supplement calcium. Initially, the animal should be given an injection (intracoelomic) of 10% (100 mg/ml) calcium gluconate at a dose of 100-200 mg/kg. This may be repeated weekly for 4-6 weeks. Oral supplementation will be necessary after the initial injection if injections are not going to be repeated. I recommend either the 10% liquid calcium borogluconate (Neocalglucon^R, Sandoz) at a dose of 1 ml/kg every day for 30 days or Pet Cal calcium tablets (600 mg) given orally with the food at a dose of 200 mg/kg/week for 30 days and then tapered to 100 mg/kg/week indefinitely.

Foods which have a desirable calcium to phosphorus ratio (greater than 1.5:1) include watercress, kale, broccoli tops, carrots, oranges, cantaloupe and raisins. Foods with poor ratios (phosphorus greater than calcium) include lettuce, tomato, cucumber, grapes, apples, pears and bananas. Current empirical literature states that iguanas should receive no animal protein in their diet even though older references recommend a small amount for juveniles.

Vitamin D3 (cholecalciferol) is the active form of vitamin D in that it facilitates calcium uptake in the gut. In nature, sunlight converts D to D3 but indoors the aquarium may require artificial UV light. There has been much debate on this topic in the reptile keeping world. Ultraviolet light in the 290 -320 nanometer wavelength converts D to D3 in nature. Vitalite (Durotest Corp., Lyndhurst, NJ) and Colortone 50 (Westinghouse, Somerset, NJ) are two brands that appear to provide proper UV wavelengths. Some herpetoculturists combine one of these bulbs with a black light bulb to achieve more ultraviolet rays.

5.  Hypervitaminosis D. Most common in green iguanas over supplemented with vitamin D. Blood vessels, renal tubules and other structures may become calcified. Radiographs used to monitor a supplemented iguanas progress may help prevent this condition.

6.  Fractures. Most commonly associated with MBD. In these cases the calcium imbalance must be corrected in order for normal bone healing to occur. Do not attempt to apply internal or external fixators on bones with thin cortices. Each fracture must be evaluated independently but in the paired long bones (radius/ulna; tibia/fibula) if only one of the two is fractured (which is common) the other bone may act as a natural splint for the fractured bone. Mid-shaft humeral fractures may be aligned and immobilized by bandaging the limb against the side of the body for 2-3 weeks or until an adequate callous has formed. Fractures of the digits will usually heal nicely when the diet has been corrected. Attempting to repair a fracture without correcting nutritional imbalances will prove to be unproductive.

7.  Prolapsed Hemipenes. Owners quickly recognize this condition. It may present as a unilateral or bilateral problem. If treated early it may be possible to reduce the hemipene and then loosely purse-string the cloaca closed (leaving enough of an opening for urates and feces to pass). If the hemipene has been out for a period of time it will appear inflamed or even necrotic. In these situations amputation is the best option. Reduced hemipenes will commonly reprolapse and may require amputation at a later date. A specific cause for this condition has not been determined.

8.  Neoplasia. Not commonly reported in lizards. This is partly due to the fact that only recently has a serious interest in the diseases of lizards been developed. Reported neoplasias include melanoma, lymphoma, hepatoma, myxoma, adenocarcinoma and osteochondroma.

VIII.  Infectious Diseases

1.  Bacterial Problems. Systemic bacterial diseases occur in lizards but are usually secondary to trauma or poor husbandry. The majority of lizard bacterial pathogens are gram negative and include the following genera: Aeromonas, Pseudomonas, Bacteroides, Klebsiella, Proteus and Salmonella. Numerous other bacterial pathogens have been reported but these are the most common. Clinical signs of bacterial disease might include stomatitis, pneumonia, cellulitis, dermatitis and the presence of abscesses. In order for a definitive diagnosis to be made culture and sensitivity tests must be performed. Effective antibiotics and routes of administration are included in the reptile formulary that you have been provided with. Remember that a large percentage of bacterial infections in reptiles are mixed aerobic/anaerobic and should be treated accordingly.

2.  Viral Problems. It is uncommon to diagnose a viral disease in lizards. A herpesvirus has been isolated from green iguanas and green lizards (Lacerta viridis) but the presence of a virus does not necessarily mean that it is pathogenic. As lizards and other reptiles are more thoroughly examined it is likely that more viral diseases will be described.

3.  Fungal Problems. These diseases are uncommon in lizards. Proper nutrition and cage hygiene will greatly reduce the threat of fungal disease. Most fungal diseases are either superficial or deep. Candida and Aspergillus are the most common fungal organisms cultured. When present there is usually an underlying problem which has lead to an immunocompromised animal. Fungal problems will sometimes respond to medical treatment.

4.  Protozoal Parasites. A number of protozoa appear to be normal inhabitants of the lizard gastrointestinal tract. These include Balantidium, Paramecium, and Nyctotherus (all of which are ciliates). Very young lizards have even been observed to ingest conspecific feces in order to establish an appropriate gut flora. Such "commensal" organisms will only present a problem when the host's immune system has been compromised. Amoebiasis, caused by Entamoeba invadens, is the most serious protozoal parasitic disease of lizards. Clinical signs include depression, anorexia, rectal prolapse, diarrhea and even acute death. Diagnosis is made by identifying amoebic cysts in the feces. Amoebic trophozoites destroy the mucosal lining of the intestine and may even become systemic. The disease can be treated with metronidazole at a dose of 125 mg/kg repeated in two weeks (see formulary). The second most serious protozoal parasite of lizards is the coccidian parasite Cryptosporidium. This parasite is a serious problem in snakes where it is normally found in the stomach. Snakes with this condition are chronic regurgitators while lizards usually do not regurgitate but continue to lose weight. No effective treatment has been identified but workers have observed some positive results with trimethoprim sulfa at an exaggerated dose of 60 mg/kg SID for 60 days. The best way to challenge this disease is through prevention. Any new lizard being added to a collection should be quarantined and any materials (including hands and water bowls) should be disinfected before being placed in different cages.

Numerous other protozoans have been found in lizards and the interested student may check the reference section for more information.

5.  Helminth Parasites. Primarily internal parasites of lizards, this group includes dozens of ascarids, strongyloids, threadworms, hookworms, lung worms, acanthocephalans, flukes and tapeworms. Pages would be required to even introduce these parasites. It is certain that animals in the wild do quite well with moderate parasite loads but with the stresses of captivity they may become debilitated by helminths. Fecal examination is the best way to diagnose most of these problems and treatments utilize some of the same medications used in mammals (see the reptile formulary included with these notes).

IX.  For More Information

1.  Adler, K and T Halliday. All the World's Animals; Reptiles and Amphibians. Torstar Books, New York, 160 pp., 1986.

2.  Anderson, N.L. Husbandry and clinical evaluation of Iguana iguana. Compendium on Continuing Education for the Veterinary Practitioner, 13(8):1265-1272, 1991.

3.  Anderson, N.L. Diseases of Iguana iguana. Compendium on Continuing Education for the Veterinary Practitioner, 14(10):1335-1343.

4.  Balsai, M. The General Care and Maintenance of Savannah Monitors and Other Popular Monitor Species. Advanced Vivarium Systems, Lakeside, Ca, 55 pp., 1992.

5.  Barten, S.L. The medical care of iguanas and other common pet lizards. In Quesenberry and Hillyer (eds): The Veterinary Clinics of North America, 23:6, 1213-1249.

6.  Boyer, T.H. Common problems and treatment of green iguanas (Iguana iguana). Journal of the Association of Amphibian and Reptile Veterinarians 1(1): 8-11, 1991.

7.  Boyer, T.H. Green iguana care. Journal of the Association of Amphibian and Reptile Veterinarians 1(1): 12-14, 1991.

8.  DeNardo D. et al. Dystocia Roundtable. Journal of Herpetological Medicine and Surgery, 10(2):8-17, 2000.

9.  Frye, F.L. Biomedical and Surgical Aspects of Captive Reptile Husbandry (Vols. I & II). Krieger Publishing Co., Malabar, FL, 637 pp., 1991.

10. Frye, F.L. and W. Townsend. IGUANAS: A Guide to Their Biology and Captive Care. Krieger Publishing Co., Malabar, FL, 166 pp., 1993

11. Frye, F.L. & Williams. Self-Assessment Color Guide to Reptiles and Amphibians. Iowa State University Press, 1996.

12. Jacobson, E.R. and G.V. Kollias. Exotic Animals; contemporary Issues in Small Animal Practice, vol. 9. Churchill Livingstone, New York, 328 pp., 1988.

13. Mader, D.R. Reptile Medicine and Surgery. Saunders Co., Phila., 512 pp., 1996

14. Marcus, L.C. Veterinary Biology and Medicine of Captive Amphibians and Reptiles. Lea and Febiger, 239 pp., 1981.

15. Journal of Zoo and Wildlife Medicine, Reptile and Amphibian Issue, 25:1, 1994.