Greg Lewbart M.S., V.M.D., Dipl. ACZM
There are close to 2400 species of snakes throughout the world. Only the Arctic regions, Antarctica, Iceland and Ireland along with a few other very small oceanic islands lack the presence of snakes. The suborder Serpentes belongs in the order Squamata which contains both the lizards and snakes. There are 10 recognized families of snakes containing 417 genera. Snakes come in a variety of shapes and sizes but all have scales, are cylindrical in shape and lack legs and external ear openings. They range in size from about 10 cm to over 10 meters.
II. Anatomy and Physiology
The following facts are important to know but most are guidelines rather than hard fast rules.
1. Most snakes have 6 rows of teeth, 4 are in the upper jaw attached to the palatine and maxillary bones and 2 in the lower jaw, one attached to each of the mandibles. All teeth can be periodically shed and replaced (including venom fangs).
2. Snakes lack eyelids and the eye is covered by a transparent scale called a spectacle. This spectacle or "lens cap" is shed when the snake under goes ecdysis.
3. Snakes lack an external ear opening but do have an inner ear which aids in balance.
4. Some snakes, including the boids and vipers, possess heat sensing pits located on the external surface of the face and jaws.
5. Snakes do not see particularly well but are good at detecting movement.
6. Snakes can extend their glottis anteriorly when swallowing prey. This adaptation for breathing is possible because of an elastic ligament at the mandibular symphysis.
7. Snakes frequently flip their tongues as a means of chemosensory detection. Most snakes possess "taste buds" in the roof of their mouth in a structure commonly referred to as "Jacobson's organ." The tip of the tongue flips scent particles up to this organ.
8. Most species have one functional lung (the right) and there is no diaphragm. The vestigial left lung forms an air sac in some species.
9. The stomach is fusiform (other reptiles have an "S" shaped stomach).
10. The liver is fusiform (other reptiles have bi-lobed livers) and like all reptiles a gall bladder is present. The pancreas is adjacent to the duodenum and the spleen may be attached to the pancreas.
11. Snakes have more than 200 vertebra (some more than 400). Each vertebra has a pair of ribs that protect the internal organs.
12. Snakes have two kidneys with the left kidney lying behind the right.
13. Locomotion is accomplished by moving the large ventral scales in groups, by lateral undulatory musculoskeletal contractions, or in some cases, both methods are employed.
1. Simple diagnostics like blood sampling, radiography and physical examination do not require anesthesia. Larger snakes may require an extra handler or two for proper restraint.
2. As with lizards, many injectable and inhalant anesthetic agents have been used. The use of injectable barbiturates should be discouraged since there are several reports of anesthetic death. Snakes may be masked down with 3% isoflurane or placed into an induction chamber (an aquarium works well) that contains isoflurane. Snakes are easy to intubate due to the prominent glottis which opens into the trachea. Depth of anesthesia can be monitored by heart rate (the heart is located about one quarter of the length of the snake from the head and can be observed beating on the snake's ventral surface) and respiratory rate. A portable doppler apparatus works well for heart monitoring. Special care should be taken to observe respiration since all of a snake's breathing is facilitated by the abdominal muscles (they lack a diaphragm). Snakes that are not breathing may be "bagged" and care should be taken to avoid a large dead space (their lung...and they only have one...is much smaller than those of dogs and cats). Ketamine is a good injectable anesthetic agent for snakes when used at approximately 30-75 mg/kg. Recovery times may be prolonged (hours to days). Anesthetized snakes should be kept between 70 and 80 degrees F and should be recovered at the same temperature. The highly lipid soluble isoflurane may cause a problem if a reptile is warmed up after anesthesia since the animal could fall back into an anesthetic state. Anesthetic agent doses are listed in the reptile formulary provided.
3. Hydration is an important consideration when dealing with surgery and anesthesia. Lactated ringers and physiological saline solutions work well on snakes, as does a 1:2 dilution of the two respectively (sometimes called "reptile ringers"). Guideline maintenance values are 15-25 ml/kg/day. A subcutaneous route is the easiest way to administer parenteral fluids in snakes although oral and intracoelomic routes can be advantageous.
IV. Blood Collection and Hematology
1. Toenail clipping is not an option. The easiest and safest way to obtain a blood sample from a snake is via the caudal vein. Pick an area slightly caudal to the cloacal opening and carefully place the needle at about a 60-80 degree angle between the scales until resistance from the vertebral bone is felt. Applying gentle negative pressure and slightly withdrawing the needle should reveal blood in the hub of the needle. A heparinized syringe is recommended. EDTA causes lysis of red cells in most reptilian samples. Another frequently employed method is cardiocentesis. The heart is visualized and a needle is directed into the apical area of the beating organ. Sterile preparation of the blood collection site is recommended. Most clinicians feel this is a safe and efficient of blood collection in snakes. This has been our experience here at NCSU. Cardiac puncture is recommended for euthanasia in snakes. In larger snakes, the highly visible palatine-pterygoid veins in the mouth may be used to obtain a small sample.
2. Snakes, like all reptiles, have nucleated red blood cells and a full complement of leukocytes as well as thrombocytes to facilitate clotting. Hematopoiesis occurs in the spleen, liver, and bone marrow. Reference ranges can be found in a number of texts and review chapters as well as the Carpenter, Mashima, Rupiper formulary (Saunders, 2001).
V. Non-Infectious Diseases
1. Thermal Burns. Very common problem with snakes. Reptiles are attracted to heat but may not realize that they are being burned by a hot rock or other device. Severe wounds may require systemic antibiotics and fluids. Superficial wounds may be managed topically with SilvadeneR Cream (silver sulfadiazine).
2. Rodent Bites. Another common problem. Owners may leave a live rodent in a cage and if the snake does not subdue it on its first attempt the snake may retreat. Rodents (especially rats) may actually bite or even eat portions of the snake. The client needs to be educated on the dangers of feeding live food. The snake's wounds should be treated openly with antibiotic ointments. Severe wounds (down to the musculature or into the coelomic cavity) should be treated with systemic antibiotics and fluids.
3. Impaction. Not particularly common among snakes but does occur. Usually due to improper cage substrate (corn cob, wood chips) becoming lodged in the gastrointestinal tract. May require surgery. Diagnosis made from history and radiographs.
4. Egg/embryo Retention. Occasionally seen in the egg laying pythons and live bearing boas. Hysterotomy (salpingotomy) and subsequent removal of the eggs/embryos is the treatment of choice. It may be possible to lubricate the oviducts with a lubricating jelly and manually assist the removal of the eggs or injecting oxytocin at a dose of 3-10 IU/kg before attempting surgery. Radiographs will help with the location and number of eggs/embryos present.
5. Blister Disease.- This problem usually is secondary to high humidity and poor cage hygiene. Snakes will present with necrotic and inflamed ventral scales. The problem is frequently multifocal. Treatment includes correcting the environmental problems and treating the lesions topically with betadine or nolvasan ointments/solutions. Severe cases may warrant the use of systemic antibiotics to prevent sepsis. The old damaged scales with be removed with subsequent sheds.
6. Dysecdysis. Refers to an incomplete or retained shed. A common problem which may be secondary to low humidity, poor nutritional status, or any number of underlying disease processes. Snakes should be soaked in warm water for up to an hour and the retained skin should be carefully removed piece by piece. Special care should be taken in the ocular regions where the retained spectacles exist. Multiple retained spectacles can lead to infection and even blindness. Do not let the client try and remove retained spectacles. The best approach is to moisten the eyes with warm water and use a pair of fine jewelers forceps to elevate some scales peripheral to the eyes and then gradually remove the attached lens cap(s). Snakes with retained spectacles frequently will not feed creating a vicious cycle and perpetuating the demise of the animal.
7. Prolapsed Hemipenes.- This condition is relatively common and may have a variety of causes. Prolapse may be unilateral or bilateral. If attended to quickly, a lidocaine gel may be applied and the organ reduced manually. A loosely attached absorbable purse string suture may be used to partially close the cloaca to prevent prolapse. This suture must allow for urinary and fecal wastes to pass and may be left in place for between 2 and 3 weeks. A second prolapse may require amputation (if the problem is unilateral the snake can still be a breeding animal since they have two separate reproductive tracts). Rectal prolapses occur but are less common. They can be treated in a similar manner but ultimately may require surgery and a pexy procedure.
8. Gout.- The deposition of urates in the kidneys, other organs and joints is usually secondary to dehydration but can be caused by primary renal or metabolic disease. Tophi may be visible on radiographs. Proper hydration and a balanced diet is the best way to prevent this disease.
VI. Infectious Diseases
1. Stomatitis.- Also called ulcerative stomatitis or "mouth rot," it is one of the most common disease problems of snakes. The disease begins with the appearance of excessive saliva or mild petechiae in the mouth. Snakes will usually go off feed and the oral mucus membranes will become more inflamed and ulcerative. As the disease progresses osteomyelitis may develop and teeth will loosen and fall out. The head may become quite swollen and the infection can become systemic. At this stage the prognosis must be guarded. Stress from poor husbandry usually precipitates the problem. Bacteria frequently cultured from these lesions include Aeromonas, Pseudomonas, Proteus, and Citrobacter. Treatment should be both topical and systemic. The oral cavity should be flushed at least once daily with a Nolvasan (0.5%) or povidone iodine (1%) solution. A topical antibiotic ointment can be applied (silver sulfadiazine cream) and in advanced cases injectable enrofloxacin (5-10 mg/kg SID for 10 days) or amikacin (2.5 mg/kg every other day for 5 treatments) should be used. An antibiotic effective against anaerobic bacteria such as clindamycin (5.0 mg/kg q. 24 hours) should also be included in the treatment regimen. Increasing the environmental temperature along with medical treatment will greatly increase the chances of recovery from this disease. It is not unreasonable to bring the cage temperature to 90-95 degrees F when a snake is ill. Some workers recommend injectable vitamin C (10-20 mg/kg SID, IM) as an aid to facilitate healing in cases of mouth rot.
2. Respiratory Disease. It is very common to see snakes with upper, lower or combined respiratory disease. Snakes present clinically with open mouth breathing, nasal discharge, audible wheezing and increased lung sounds on auscultation. The history will usually include inadequate environmental temperatures or the recent addition of a new animal to the cage or collection. Bacteria are commonly involved and the best treatment is to combine antibiotic, fluid and heat (see above) therapy. Fungi can also be involved and may be seen via culture or histopathology on necropsy. Snakes which are not eating and appear thin should also be tube fed.
3. Paramyxoviral Disease. Caused by an rna virus named Ophidian Paramyxovirus (OPMV). Has been described from several species of snakes. Clinical signs include anorexia, regurgitation, head tremors, "star gazing," and respiratory difficulty. Clinical signs may last up to 10 weeks before the animal succumbs. Animals may ultimately die of secondary bacterial diseases. Antibiotics and supportive care are warranted. Diagnosis is made from the history (recent exposure to non-quarantined animals), hemagglutination-inhibition antibody titer, and histopathology and electron microscopy. The virus has never been isolated from a live animal so definitive antemortem diagnosis is not possible. When this disease is suspected, strict isolation and quarantine protocols must be adhered to. New animals should be quarantined for at least 90 days before being exposed to other animals in the collection.
4. Inclusion Body Disease. Also known as IBD, this disease appears limited to the boid family (boas and pythons). It has been documented for nearly 20 years and a recent article described the disease in detail. The causative agent appears to be an RNA virus, perhaps belonging to the Retrovirus group. Clinical signs include regurgitation, head tremors, ataxia, and incoordination. As a rule, boas tend to regurgitate and the pythons display tremors, disorientation, and appear flaccid. There is no treatment and diagnosis is made upon histological and transmission electron microscopical examination of the brain, spinal cord, liver, pancreas, and kidney. Affected snakes have eosinophilic intracytoplasmic inclusion bodies in the cells of the above mentioned tissues. IBD is a serious disease and quarantine, disinfection, and isolation should be used judiciously to prevent its spread.
5. Protozoal Parasites. Snakes harbor a number of internal protozoans and not all are pathogens. The two most important protozoal diseases of snakes are amoebiasis (Entamoeba invadens) and cryptosporidiosis (Cryptosporidium sp.). Clinical signs of amoebiasis include anorexia, bloody diarrhea, rectal prolapse and acute death. Diagnosis is made by identifying amoebic cysts in eosin stained feces (the cysts do not pick up stain and stand out as white spheres). Treatment is with metronidazole (see formulary). The life cycle is direct and certain species of snakes and other reptiles will act as carriers but never show clinical signs.
Cryptosporidiosis is being reported more frequently every year in snakes. Some specimens will shed oocysts in feces for years without any clinical signs. Sick animals will have a thickened gastric mucosa. A swelling of the animal may appear near the mid-point of its body. Clinically affected animals regurgitate food within a few days of feeding. Antemortem diagnosis may be made by locating oocysts in the feces either by examining unstained smears or with the aid of a DMSO acid fast stain. Post mortem changes include a much thickened gastric mucosa and organisms will be seen on histopathology. There is no proven treatment for this disease. Any suspect snake should be quarantined and any object or potential fomite should be disinfected before transfer form cage to cage.
6. Helminth Parasites. Many species of nematodes, trematodes, acanthocephalans and cestodes infect the snakes of the world. We do not have the space or time to discuss these in detail. Most of these problems can be diagnosed on fecal examination. Nearly all of the helminth parasites respond well to standard veterinary parasiticides. Refer to the reptile formulary which has been included with your notes for doses and treatment regimens.
7. Arthropod Parasites- A number of ticks and mites are ectoparasitic on snakes. There are over 250 species of snake mite parasites alone! This is also one of the more common problems the clinician in private practice will be presented with. Most mites and ticks are found in areas where there is moisture and a place to hide. The eyes, mouth and cloaca are commonly parasitized. These parasites are easily transferred from one animal to another and the history will often include a new animal in the collection. Puppy or kitten flea and tick spray can be gently applied with a moist cloth once a week. The cage, bowl and hide box must be disinfected and new animals need to be quarantined. A piece of a flea collar can be put in a jar with holes at the top and placed near the top of the cage for 2-3 days. The flea collar must be securely contained so that the snake cannot come in direct contact with it. Soaking the snake daily in warm water is an excellent way to remove mites, but must be accompanied by cleaning the environment. Some clinicians use injectable ivermectin to kill arthropod parasites of snakes (see formulary).
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. Frye, F.L. Biomedical and Surgical Aspects of Captive Reptile Husbandry (Vols. !&II). Krieger Publishing Co., Malabar, FL, 637 pp., 1991.
3. Frye, F.L. & Williams. Self-Assessment Color Guide to Reptiles and Amphibians. Iowa State University Press, 1996.
4. Jacobson, E.R. and G.V. Kollias. Exotic Animals; contemporary Issues in Small Animal Practice, vol. 9. Churchill Livingstone, New York, 328 pp., 1988.
5. Jacobson, E.R. and J.M. Gaskin. Illness associated with paramyxo-like virus infection in a zoologic collection of snakes. JAVMA, 179 (11): 1227-1230, 1981.
6. Jacobson, E.R. Snakes. In Quesenberry and Hillyer (eds): The Veterinary Clinics of North America, 23:6, 1179-1212, 1993.
7. Mader, D.R. Reptile Medicine and Surgery. Saunders Co., Phila., 512 pp., 1996
8. Mader, D.R. et. al. The hematocrit and serum profile of the gopher snake (Pituophis melanoleucas catenifer), J. Zoo An. Med. 16: 139-140, 1985.
9. Marcus, L.C. Veterinary Biology and Medicine of Captive Amphibians and Reptiles. Lea and Febiger, 239 pp., 1981.
10. McDaniel, R.C. et. al. Serum chemistry of the diamond-backed water snake (Nerodia rhombifera rhombifera) in Arkansas, J. Wild. Dis. 20(1): 44-46, 1984.
11. Schumacher, J., Jacobson, E,R., Homer, B.L., and J.M. Gaskin. Inclusion body disease in boid snakes. Journal of Zoo and Wildlife Medicine, 25:4, 511-524, 1994.
12. Tilley, M. et. al. A comparative study on the biology of Cryptosporidium serpentis and C. parvum (Apicomplexa: Cryptosporidiidae). Journal of Zoo and Wildlife Medicine, 21(4), 1990.
13. Journal of Zoo and Wildlife Medicine, Reptile and Amphibian Issue, 25:1, 1994.
14. Journal of Herpetological Medicine and Surgery (many issues)
15. Exotic DVM Magazine (many issues)