Introduction to chelonian (turtle) medicine (Proceedings)

August 1, 2011

Article

Turtles are found throughout the world on all continents and in all oceans except Antarctica. There are over 300 species of turtles (far fewer than snakes or lizards) that belong to about 90 genera in 13 families (http://www.reptile-database.org/db-info/SpeciesStat.html; accessed 7/09). Turtles appeared in the fossil record over 200 million years ago and were on earth long before mammals and other forms of present day reptiles. They occur in terrestrial, freshwater aquatic, semiaquatic, and marine environments. They range in size from 11 cm to 185 cm and one species can weigh close to a ton, making it (the leatherback sea turtle) the world's largest turtle and one of the largest living reptiles!

Anatomy and physiology:

Witherington & Wyneken (2003) have published a nice color anatomy guide for the turtle (see Further Reading).

1. Turtles can live a long time and tortoises generally live longer than aquatic species. Reports of Aldabra and Galapagos tortoises living up to 260 years exist. Some species can be aged by growth rings on the scutes, but as the animal ages accuracy suffers. This does not hold true for many aquatic species that periodically shed their scutes.

2. Both the pelvic and pectoral girdles are contained entirely within the rib cage that is fused to the protective shell. The shell is a vascular bony structure that should be included when calculating drug dosages from the animal's weight.

3. Sexual dimorphism exists in many species. Male tortoises have a concave plastron and male aquatic turtles usually have very long toenails on their front feet. The tail is relatively larger in males than in females but this does not always hold true.

4. Turtles lack teeth but most possess a sharp beak called a rhamphotheca or tomium. They also have tongues that aid in prehending food but cannot be extended beyond the mouth (as is the case with many snakes and lizards).

5. The gastrointestinal tract is standard in that it includes a simple S-shaped stomach, liver, gall bladder, pancreas, spleen, small and large intestine. A cecum may be present but fermentation, when applicable, occurs primarily in the large intestine. Nearly all aquatic turtles must eat in the water.

6. Like most other reptiles, the heart has three chambers (one ventricle and two atria).

7. Turtles lack a diaphragm and since they are housed in a shell most have little or no abdominal breathing component. Most pressure changes allowing for lung expansion are accomplished by muscles in the pockets surrounding the fore and hind limbs. Aquatic species can also respire through their skin and the mucus membranes of the throat and cloaca.

8. Turtles have paired kidneys and a cloacal opening for the urogenital and gastrointestinal tracts. The ureters open into the cloaca and urine then passes from the cloaca to the more cranial urinary bladder.

9. The chelonian cloaca is divided into three zones: the cranial coprodaeum where the rectum attaches; the medial urodaeum where the ureters and reproductive tracts attach; the proctodaeum where urinary and fecal waste are stored.

10. All turtles have internal fertilization. Courtship is usually a part of most chelonian copulation. Some freshwater species (sliders, cooters) have an elaborate ritual in which the male waves its long forelimb nails in front of the female's face. The single phallus is employed during copulation. Unlike snakes and lizards, the chelonian penis has erectile tissue. The semen is conducted through a seminal groove that terminates between distinct folds (known as plicae) of the glans. Some female turtles have a clitoris located in the ventral cloaca that anatomically resembles the penis.

11. All turtles lay eggs and most bury them in the earth. Some species may lay several clutches per year and females of certain species can store sperm for several years.

12. Sea turtles possess special salt glands in their head behind each eye that allow them to drink seawater.

-More details can be found by reading: Boyer TH and Boyer DM. 2006. Turtles, Tortoises, and Terrapins. In: Mader D.R. Reptile Medicine and Surgery, Second Edition. Elsevier/Saunders Co., Phila, 78-99.

Anesthesia/analgesia/restraint:

1. Simple procedures like radiography and blood sampling usually do not require sedation. Most turtles will remain still for the time it takes to produce a radiograph.

2. Invasive surgical procedure will require anesthesia. A number of agents are used in turtles including injectable and inhalant compounds. We have had favorable results with many chelonian species using 3-10 mg/kg propofol IV for induction or relatively quick procedures like fish hook removal. Ketamine hydrochloride at a dose of 5-10 mg/kg combined with medetomidine at 50 mcg/kg IM or IV works very well. The medetomidine is then reversed with atipamezole. This regimen may also be used in order to sedate a turtle for intubation and placement on inhalant isoflurane or sevoflurane. Telazol® is used by some clinicians to anesthetize chelonians (see formulary). Barbiturates should be avoided if possible because of deleterious effects. Butorphanol, ketoprofen, buprenorphine, morphine, and other agents have been used for analgesia in chelonians. A recent study (Sladky et al., 2007) found that morphine may be superior to butorphanol in turtles. Buprenorphine can also be used and has been studied in red eared sliders (Trachemys scripta) by Kummrow et al., 2008. Please refer to the formulary for details.

Blood collection and hematology:

1. There are several sites for blood collection in turtles. These include the caudal vein, jugular vein, supra-occipital (dorsal cervical) sinus, sub-carapacial sinus, brachial vein, and cardiac puncture. As a rule, the caudal vein is not always productive in turtles. The tail tends to be short compared to other reptiles and the shell frequently is in the way. In some cases the dorsal tail vein can be quite productive (especially in male turtles where the tail is larger). Turtles have a large supra-occipital sinus located on the lateral aspect of the head just ventral to a large ligament. This sinus is bilateral so either side may be used for blood collection. The jugular vein can be difficult to hit, especially if the turtle's head cannot be extracted. A small gauge needle place at a 45 degree angle near the lateral carpus is an excellent place to bleed smaller aquatic turtles.

2. Please refer to Diethelm (2005), Campbell (2006), and Campbell & Ellis (2007) for detailed clinical pathology reference ranges and other information.

Non-infectious diseases:

1. Abnormal beak/tomium

Some turtles and especially tortoises in captivity will develop overgrown "beaks." This is usually due to the consumption of unnatural foods. Can be corrected by trimming or grinding down with a Dremel drill that is frequently used in birds with similar problems.

2. Cracked Shell

This is unfortunately a very common problem in turtles and tortoises. Chelonians have two things working against them. They like to cross roads, and they are slow! Lawn mowers and other heavy machinery take their toll too. The wound should be flushed very well with a dilute antiseptic like Nolvasan® (1:40) with clean water, or if the coelomic cavity is exposed, a physiological saline. The older literature describes techniques to repair shells using epoxy, fiberglass, and hoof or dental acrylic. While these techniques do have value, they should be limited to fractures of peripheral shell areas not involving an exposed coelomic cavity. Here at the NCSU-CVM, we utilize open surgical techniques that will be taught to you in the turtle shell repair laboratory. Properly placed sterile bone screws and surgical wire work very well to reduce and stabilize shell fractures. The human artificial skin product, Tegaderm®, may be used to temporarily close large defects in the shell. External "heat-pliable" orthopedic materials (Orthoplast®, Hexalite®) are also effective in reducing and stabilizing shell fractures. The Piedmont Wildlife Center (PWC) has had success using an adhesive bandage called Mefix®, introduced this protocol to the NCSU-CVM Turtle Rescue Team, and we have had favorable results in some cases.

Injured turtles should also receive fluids, analgesics, and aggressive antibiotic therapy. Post-operative nursing is extremely important in the survival of "cracked" turtles. Force feeding, appropriate temperature, rest, and access to fresh water are a must.

While the shell is protective, it also makes diagnosis of internal injuries very difficult. Simply repairing the shell and restoring it to its original appearance does not produce a "cured" turtle or tortoise. I have seen turtles live for weeks with severe internal injuries before succumbing to peritonitis. We generally do not feel a turtle is releasable until it is eating on its own and has been allowed to recuperate for at least 3 months.

3. Hypovitaminosis A

Usually a disease of freshwater aquatic turtles. Turtles frequently present with swollen eyes, a nasal discharge, tympanic (aural) abscesses, and in advanced cases, respiratory distress. The condition is especially common in captive box turtles and small freshwater aquatic turtles that may be receiving an inadequate diet. The lack of vitamin A results in metaplasia of squamous cells that causes a decrease in mucus production and an increase in the production of keratin. Animals should initially receive a parenteral dose of vitamin A (see formulary) and then should be placed on a well balanced diet that contains appropriate levels of vitamin A. Dog and cat foods as well as some of the commercially available reptile "sticks" and pellets provide adequate levels of vitamin A. Care should be taken not to over supplement with vitamin A (see below). There is some evidence that environmental organochlorine toxicity inhibits vitamin A metabolism in wild box turtles and contributes to aural abscesses and upper respiratory disease (Holladay et al., 2001).

4. Hypervitaminosis A

This problem occurs secondary to administration of supplemental vitamin A. Clinical signs include sloughing of the skin and secondary bacterial infections of the exposed tissues. To prevent this condition, turtles should receive just a single dose of injectable A followed by a change in the diet or perhaps oral vitamin A supplementation in the form of cod liver oil that can be dabbed onto the food or tomium.

5. Metabolic bone disease

Certainly not the problem it is in iguanas but it does occur in turtles and tortoises. Turtles fed primarily organ meats (liver, heart) or pure muscle (beef, pork, chicken) will develop metabolic bone disease and other nutritional problems. If these foods must be fed they need to be supplemented with calcium and multivitamins. Crickets and mealworms are two insect foods that have a poor calcium to phosphorus ratio (more phosphorus than calcium). Some people "shake and bake" these insects with powdered vitamin and calcium supplements before feeding and others simply feed the insects powdered milk to increase their nutritional value.

6. Egg retention (dystocia)

Dystocia appears to be a fairly common problem among captive turtles. A number of factors have been linked to this condition including lack of appropriate nesting substrate, dehydration, hypocalcemia, poor nutrition, and trauma. Radiography is very helpful in diagnosing this problem, however, eggs can frequently be palpated digitally within the coelomic cavity. Affected animals should be given a physical examination along with a thorough history. Once the animal is properly hydrated and nourished, a suitable nesting substrate can be provided. If this conservative approach is unsuccessful, then a regimen of oxytocin (see formulary) preceded by calcium gluconate and fluids may be in order. Before using oxytocin the clinician needs to be sure there is not an obstruction. It can be difficult to determine if a turtle with eggs is truly "egg-bound." History, time of year, and egg morphology can help make this determination. Eggs can even end up in the urinary bladder, most likely from being "retropulsed" from the cloaca. Surgery and endoscopy have been used to remove such eggs.

7. Ruptured oviduct

While apparently not a common problem, turtles with obstructive dystocia are especially at risk, especially if given oxytocin or arginine vasotocin. This can be a fatal condition due to peritonitis and endotoxemia.

8. Prolapsed phallus

Owners quickly recognize this condition. If treated early it may be possible to reduce the phallus (a lidocaine gel may help with this procedure) and then loosely purse-string the vent closed (leaving enough of an opening for urates and feces to pass). If the phallus has been out for a period of time it will appear inflamed or even necrotic. In these situations amputation is the best option. While the turtle will no longer be reproductively sound, he will lead a relatively normal life since urine flows directly from the cloaca to the vent.

9. Gout

Gout has been reported in several species of turtles. Accumulation of uric acid crystals or tophi is most commonly secondary to water deprivation or a protein imbalance in the diet (see snake notes). Treatment with NSAID's and allopurinol may be warranted.

10. Shell Rot

Primarily a disease of aquatic species. Usually secondary to the turtle spending all of its time in the water or water that is of poor quality. Treated by correcting water quality problems and providing a place for the turtle to "haul out."

Infectious diseases:

1. Viral diseases

A number of viral diseases have been reported in sea turtles. Important viral diseases of freshwater and terrestrial chelonians include Herpesvirus Disease of tortoises (multiple clinical signs and high mortality may occur) and Iridoviral (Ranavirus) Disease of Box Turtles (mortality may be high and clinical signs include pharyngeal ulcers, focal skin sloughing, and marked lethargy). See Origgi FC (chapter 57, Mader, 2006) for a review of Herpesvirus Disease of tortoises and Jacobson (2007) for a review of chelonian viral diseases.

2. Bacterial problems

Like snakes and lizards, turtles are prone to a number of bacterial pathogens, most of them being gram negative. In addition to infection of traumatic wounds, debilitated chelonians are vulnerable to respiratory diseases caused by bacteria. Aquatic turtles with lung disease will frequently float in the water asymmetrically or have difficulty surfacing or submerging. Radiographs can help confirm the presence of a pneumonia (the lung fields are quite large and located in the dorsal portion of the coelomic cavity beneath the carapace). A lateral or anterior-posterior view is the best way to visualize the lungs of turtles. Culture and sensitivity tests will help in the diagnosis and treatment of bacterial diseases.

• Septic cutaneous ulcerative disease (SCUD) is a problem most frequently observed in freshwater aquatic turtles like sliders and cooters. The causative agent is Citrobacter fruendii, a Gram-negative rod. Affected animals may present with deep skin ulcers in a variety of locations.

• Mycoplasmosis, also termed Upper Respiratory Tract Disease (URTD), is a well-studied and serious disease affecting some chelonian species, especially tortoises. Affected animals generally experience a chronic infection with varying degrees of clinical signs. Mortality may occur but is rarely acute. Infected animals probably only rarely clear the organism. Treatment regimens are anecdotal but worth pursuing in some cases. Diagnosis can be accomplished by culture, plasma ELISA, or PCR testing. See Wendland et al. (chapter 73, Mader, 2006) and Jacobson (2007) for more details.

3. Fungal diseases

Turtles are prone to both superficial and deep mycoses. There are several reports in the literature of fungal granulomas in the lungs of turtles and fungi cultured from skin and shell tissues are even more common. Systemic infections are very difficult to treat and are usually secondary to a poorly functioning immune system. Superficial fungal infections can be readily treated with topical antifungal agents and proper hygiene. Decreasing the pH of the water below 6.5 may also help alleviate fungal problems. Fungi that have been cultured from superficial lesions of turtles include Basidobolus ranarum, Dermatophyton sp., Fusarium sp., and Aspergillus sp.

4. Protozoal diseases

Fortunately for turtles, they are rarely infected with Entamoeba invadens or Cryptosporidium sp. Turtles can be sub-clinical carriers of amoebiasis. There are reports of protozoans causing disease in chelonians, but by the same token, the appearance of protozoans in a stool sample does not mean there is a problem. The Hexamita /Spironucleus flagellates do cause disease in turtles, and if present in large numbers, may be treated with metronidazole. A wide variety of protozoans have been reported in turtle blood. Since these parasites are not usually a clinical problem they will not be elaborated upon but the student should be aware that they exist.

5. Helminth parasites

Turtles have their share of nematode, cestode, trematode and acanthocephalan parasites. Diagnosis is made by fecal examination and history (turtles captured in the wild will tend to have broader and heavier parasitic loads than captive raised animals). See the notes on snakes and lizards and consult the reptile formulary for drugs and doses.

6. Leeches

These parasites are strictly external and are found on many wild freshwater and marine turtles. In severe cases they may cause anemia and they can act as vectors for blood borne parasites. Treatment is by plucking them off of the turtle.

General Reference Material

Exotic DVM Magazine (published until 2011)

Journal of Zoo and Wildlife Medicine

Journal of Herpetological Medicine and Surgery

Specialty Boards

In June, 2009 the American Board of Veterinary Practitioner's (ABVP) certification in Reptile and Amphibian Medicine was approved by the AVMA and the first credentialing and examination was offered in 2010. See link below for details:

http://www.abvp.com/categories_reptileamphibian.htm

Introduction to chelonian (turtle) medicine (Proceedings)

Further reading

General Reference Material

Specialty Boards