Boa constrictor imperator Gastro Intestinal Tract with digested meal

One thing about being the editors of The Vet Gazette is you never know what is going to come through the inbox. This wonderful and truly unique submission describing a boa constrictor dissection comes from Daniel Newham (with help from Leanne Smaller) from the Royal Veterinary College. Thank you for the wonderful submission Daniel!

Introduction

Snakes have a very linear digestive system. Initial digestion by swallowing is conducted in two motions, one via muscles in the walls of the oesophagus which contracts to squeeze the food down. The second swallowing movement is specific to snakes, and involves wave movements of the backbone and body (Moon 2001).

In smaller snake species, gastro intestinal problems can happen when the snake ingests articles larger than the lumen. These can include accidental ingestion of substrate with food through inadequate husbandry.

Further diseases of the gastro intestinal tract include parasites, bacteria and viruses which are common plagues for snakes. Snakes kept in closed environments reinfection is common where many parasites can live an entire life cycle on the same host, laying their eggs in the host's intestines which are then passed out in their droppings only to then reinfect the host again. Good husbandry management is necessary to mitigate reinfection risk (Johnson 2012).

Objectives

• Display the gastrointestinal tract in situ

Materials

The materials needed in this dissection include: boa constrictor, a blunt metal probe, a pair of scissors, a scalpel, a pair of rat-toothed and blunt tweezers.

8mm and 18mm tubes for supporting structures.

Methods

Ventral parallel incisions were made just caudal to the head running the length of body finishing three scutes cranial to the vent. The incisions followed at the level of the ventral end of the ribs approximately two scales width dorsal to the scutes.

The tail vein was removed (coccygeal vein) along with the most superficial epaxial muscles (Mm. semispinalis-spinalis, longissimus dorsi and iliocostalis) exposing the internal visera and paired coelomic adipose stores.

A left sided section of skin was reflected just caudal to the head to reveal the upper oesophageal tract. The pleura surrounding the tract is closely associated with that surrounding the carotid arteries and trachea, the muscles ribs and pleura were removed to reveal the opening to the head gut, trachea and carotid arteries. A small section exposing the different layers of muscles ribs, oesophageal wall (with membrane containing sensory nerves) was exposed and a window of tissue was cut and reflected in the oesophageal wall to expose the lining of the oesophagus. A 18mm tube was inserted from this window to the mouth to support this area for plastination.

Clinical note: The wall of the upper oesophagus appears thin and easily damaged and retains its integrity through close association with the connective tissues of the surrounding muscles (and trachea), though apparently not damaged by ingestion of large prey it may prove an area prone to iatrogenic damage by the surgeon. The delicate nature of the upper oesophagus could also be due to degradation of specimen.

Caudal to this area (1/8 of the body length from the head) the oesophagus changes from bridging the entire width of the body to running to the left and dorsal of the trachea. Some connective tissue was reflected to expose the path of the oesophagus and around the thyroid to show it in situ lying ventrally across the trachea and oesophagus (1/4 from the head).

Clinical note: Caudal to the thyroid (3/8) the trachea and oesophagus are obscured by the fat pads of the cardiac region, the cranial 2/3 of these were removed to show the oesophagus running closely within connective tissue dorsal to the major cardiac vessels and trachea.

Bifurcation of trachea and association of oesophagus and left lung. Oesophagus runs along left side of liver with left lung. Level with the last third of the liver (1/2) is the division on oesophagus and stomach. The ventral fat pads moulded over the liver lungs and oesophagus, were removed. Caudal to the liver the fat pads also run centrally alongside the stomach and intestine, these were also removed. Removing the fat pads exposed protective pleural covering the abdominal organs and associated circulatory system. This connective membrane was carefully pared and removed exposing portal vein running within a secondary membrane (dorsal to the caudal liver). The membranes attaching stomach to spleen, pancreas and gall bladder were also removed.

Clinical note: there is a significant gap (approximately a third the length of the stomach) between the caudal end of the liver and the spleen and gall bladder. This area is filled with convulsions of vessels running to and from the organs, including the portal vein and distinctive (two vessels that run alongside each other in a separate pleura). The entire ventral surface of the spleen and part of the gall bladder and covered by a mass of vessels that would make surgical access difficult. Additionally, the spleen lies medial to the stomach and as with all these vessels is closely associated by connective tissue/ pleura.

The snake was gravid and the intestines had been displaced dorsally by the presence of multiple eggs. The mesentery of the small intestine closely is associated with the ovaries and more caudal with the oviduct and kidneys. The left ovary runs dorso-lateraly to the small intestine which runs more medially as it becomes the large intestine.

The ingesta in the boa’s large intestine though small meant the intestine ran medial to both pairs of kidneys and ovaries. The connective tissue was paired and the mesentery partially separated at its dorsal wall attachment to allow the oviducts and kidneys to be partially reflected. Parallel to the dorsal two thirds of the left kidney the snake had an area of intestine with a thicker more muscular appearance. This area appeared to contain ingesta. On palpation most of the area was soft with the most cranial part feeling firmer. A window was cut and reflected in this area revealing a mix of thick liquid and hair. Further investigation revealed a canine tooth of a small rodent.

Fat pads and connective tissue were removed down to the level of the vent, an 8mm tube was inserted into the vent to support the cloaca and demonstrated the merging of the intestine and oviducts just cranial to the vent.

Discussion

If indigestion and loss of appetite is caused by impaction surgical intervention of impaction can be challenging. Rehydration and administration of lubricants and food may allow passage of some foreign bodies. However, in the case of complete obstruction, surgery to remove impactions and foreign bodies may be challenging for smaller patients. Small suture and careful tissue handling must be used to prevent stricture (Johnson 2012).

In many cases however, indigestion is caused by parasites (Veterinärmedizinische Universität, 2011). There are many parasites that can have adverse impacts on snakes, such as hookworms, roundworms and cryptosporidiosis to name a few. Given the brevity of this document, just a few will be mentioned. Infections of hookworms in the upper gastrointestinal tracts, can cause attachment wounds and can leave large mineral deposits, in turn causing impaction (Pets4homes 2016).

Regurgitation of partially digested food and little appetite can also indicate roundworms. Again, these worms leave mineral deposits in the reptiles gastrointestinal tracts which can be tender. If the wounds are left untreated, they can cause holes in the gut. Parasite burdens can be identified through analysis of droppings. Treatment is essential using prescribed products specific to the species (Johnson 2012).

Clinical signs of cryptosporidiosis in snakes may include anorexia, lethargy, intermittent or chronic regurgitation of undigested prey several days after feeding, chronic weight loss, and firm mid-body swelling caused by gastric hyperplasia (In Practice 2015).

Conclusion

We found the snake dissection challenging to compared to other available references due to the range of species differences. Particularly the spleen, stomach and gall bladder.

The dissection was a lengthy process and due to the tight association of the surrounding tissue to the organs made the organs appear to be very delicate. What was surprising was the thin tissue of the oesophagus but whether this was a post mortem artefact or would be delicate during an operation would remain to be seen.

Veterinary Students in Research

This winning submission to our Cases and Abstracts category comes from Tierra Rose from Purdue University. The abstract is from her summer research project at Stanford University School of Medicine that focused on temporal lobe epilepsy in sea lions along the Monterey Bay region of California due to domoic acid toxicity. Great job Tierra!

Loss of parvalbumin-immunoreactive interneurons in epileptic California sea lions

Tierra Rose¹, Starr Cameron², Raisa Glabman3, Emily Abrams², Shawn Johnson4, Frances Gulland4, Paul Buckmaster²

¹Purdue University, College of Veterinary Medicine, West Lafayette, IN
²Stanford University, School of Medicine, Department of Comparative Medicine, Stanford, CA
³University of Pennsylvania, School of Veterinary Medicine, Philadelphia, PA
4Marine Mammal Center, Sausalito, CA

Temporal lobe epilepsy is common in humans. Seizures typically originate in the hippocampus, but the cause is unknown. The hippocampal dentate gyrus of human patients displays neuropathological abnormalities, including the loss of parvalbumin-immunoreactive interneurons. Normally, parvalbumin interneurons strongly inhibit excitatory neurons. Loss of parvalbumin interneurons in temporal lobe epilepsy might cause seizures. Rodent models of temporal lobe epilepsy fail to replicate the parvalbumin interneuron loss found in human patients, so better animal models are needed. California sea lions (Zalophus californianus) develop temporal lobe epilepsy after exposure to the excitatory neurotoxin domoic acid, which enters the marine food chain during harmful algal blooms. We hypothesized that epileptic sea lions would display significant loss of parvalbumin interneurons in the dentate gyrus. To test this hypothesis, sea lions were intracardially perfused with formaldehyde immediately upon euthanasia because of failed response to treatment and poor prognosis. Brains were sectioned (40 μm) coronally. Hippocampi were isolated and processed for parvalbumin-immunocytochemistry. Stereology and a Neurolucida system are being used to estimate the number of parvalbumin-positive interneurons per dentate gyrus. Preliminary data suggest that epileptic sea lions display severe loss of parvalbumin interneurons, similar to human patients with temporal lobe epilepsy. If confirmed, these findings would suggest that epileptic sea lions can be used as a large animal model of human temporal lobe epilepsy. Sea lions could serve as candidates to test novel anti-epileptogenic treatments before human clinical trials.

Student: Supported by NIH Office of the Director, Division of Comparative Medicine
Research: Supported by NSF and NIH (NINDS & OD)

"Optimization of ultrasound settings for better determination of cystolith size in vitro"

Thank you to Lauren Kustasz from Michigan State University for sharing the abstract from her summer research project with Dr. Nathan Nelson DACVR....and CONGRATULATIONS on having it be selected as a winner in the cases and abstracts category.

Accurate estimation of urinary cystolith size is a critical factor in assessing the biological behavior of urocystoliths, their response to dissolution therapy, and their potential for removal by minimally invasive procedures. A previous study found that ultrasound, using a curved array transducer at a frequency of 10 MHz, overestimated cystolith size compared to other imaging techniques. The purpose of this study was to further evaluate ultrasonography as an imaging technique for measuring cystoliths, comparing transducer types, different frequencies, and the use of tissue harmonics imaging and spatial compound imaging using an in vitro bladder phantom model. Thirty cystoliths were imaged using combinations of the ultrasound variables mentioned. The accuracy of cystolith measurement was determined by taking the difference between the measurement obtained from the ultrasound image and the true size of the cystolith determined by a digital caliper. The accuracy of the measurements obtained from the linear transducer was significantly greater than the accuracy of the measurements obtained from the curved array transducer (p < 0.05). Measurements from the linear transducer showed a significant decrease in accuracy of cystolith size estimation when spatial compound imaging was used (p < 0.05 ). Independent of actual cystolith size, the linear transducer tended to overestimate cystolith size by 0.16 cm on average and the curved transducer overestimated by 0.43 cm on average. Subjectively, there were more artifacts seen in the images taken with the curved transducer and, especially with smaller cystoliths, these artifacts superimposed the cystoliths making them difficult to measure.

Dr. Nelson and the author with their ultrasound machine

GENE THERAPY TO PROVIDE ROD FUNCTION IN CNGB1-/- DOGS WITH ESTABLISHED ROD LOSS.

Lauren E Kustasz won best oral presentation given by a veterinary student at our school's annual Phi Zeta Research day for her summer research project.  Check out her interesting work below, and congratulations to her on her Cases/Abstracts Award!

GENE THERAPY TO PROVIDE ROD FUNCTION IN CNGB1-/- DOGS WITH ESTABLISHED ROD LOSS.

Lauren E Kustasz-1, Laurence M Occelli-1,2, Paige A Winkler-1,2, Simon M Petersen-Jones-1,2

1) College of Veterinary Medicine, 2) Department of Small Animal Clinical Sciences, Michigan State University.

Progressive Retinal Atrophy (PRA) is a genetically heterogeneous hereditary disease that causes photoreceptor degeneration in dogs and is equivalent to Retinitis Pigmentosa in humans. The phenotype and mechanism as well as potential therapies have been studied in a colony of dogs with autosomal recessive PRA due to a mutation in Cngb1. In this disease, prior to rod death, there is a shortening of rod outer segments and deterioration of the photoreceptors as early as 8 weeks of age. We hypothesize that there is a stage during retinal degeneration after which gene therapy will no longer be able to rescue rod function or prevent rod cell death. The objectives of this study were to determine the success of gene supplementation in Cngb1-/- dogs and to assess the stage of retinal degeneration at which gene therapy can still restore useful visual function. Five Cngb1-/- dogs with different degrees of rod degeneration and loss (ages range from 3 to 10.5 months) were injected with the same AAV5 GRK1-cCNGB1 vector. The degree of restoration of rod function was assessed by electroretinography (ERG) and vision testing. The thickness and morphology of the photoreceptor layers was assessed using Spectral Domain-Optical Coherence Tomography in vivo. We found that dogs injected at 3, 5 and 6 months of age showed a larger improvement of rod-mediated ERG amplitudes and improved vision rescue in low light intensities compared to the dog treated at 10.5 months. This study shows that although successful in providing rod function, gene therapy is more effective in Cngb1-/- dogs with earlier stages of rod photoreceptor loss.

Feeling Bloated?

Hydrops and Hydrocoelom in a Green Frog

Amanda Igeta, Colorado State University, DVM Candidate 2016

Signalment

Green Frog (Rana clamitans), male, approximately 2 years old

History

An approximately 2 year old wild-caught Green Frog was presented for a 1 week history of generalized swelling and a 1 day history of anorexia. He is housed alone in a half aquatic 20 gallon tank with a stone substrate, a hide box, and fake branches. The temperature is maintained at 75 degrees F with a room humidifier and heater. A canister is used to filter the water, and the water is changed monthly with tap water. The daily diet consists of crickets and a multivitamin. 

Physical exam

On physical exam, he was quiet, alert, and responsive. The coelom and hind limbs were swollen and edematous, and transillumination of the coelom revealed no abnormalities. The eyes were clear, though there were red abrasions ventral to both eyes and a bloody discharge from the left naris. Oral examination revealed swelling of the dorsal aspect of the mouth, located ventrally to the eyes. He was able to ambulate on all four limbs, though there were noticeable musculoskeletal deformities of the long bones, which were softened and mildly rubbery on palpation. A 1 cm diameter, dark red swelling was present on the caudal aspect of the dorsum in the region of the cloaca.

 

Differential diagnoses

Initial differential diagnoses for hydrocoelom and hydrops include renal failure, lymph heart failure, and liver disease. The underlying etiologies of these organ failures vary and may include bacterial (Mycobacterium) or fungal infections (Batrachochytrium dendrobatidis) that are often secondary due to poor husbandry, malnutrition leading to immunosuppression or hypoproteinemia, osmotic imbalances, and hypocalcemia which can lead to decreased function of the lymph hearts. Differential diagnoses for the musculoskeletal abnormalities and the mass in the region of the cloaca include metabolic bone disease and cloacal prolapse, respectively.

Diagnostics

It was decided that we would drain the subcutaneous and intracoelomic fluid and analyze it via cytology and refractometry. On presentation, the frog was 145 g. Celiocentesis was performed with a 25 gauge butterfly needle attached to a 6 cc syringe. Prior to puncturing the skin, the coelom was transilluminated in order to identify and avoid any organs or blood vessels, and 29 mL were aspirated. The same procedure was repeated for the right and left hind limbs, which yielded a total of 27 mL. A total of 56 mL of a serosanguinous fluid were removed from the frog to yield a new body weight of 89 g. The total protein of the fluid was 0.2 g/dL. Direct microscopic examination and a diff-quick stain of the coelomic fluid revealed 3+ erythrocytes. A gram stain did not reveal any bacteria, though there was a moderate amount of proteinaceous debris.   

VD whole body radiographs were taken after the 56 mL were aspirated from the frog. The radiograph revealed an increased soft tissue/fluid opacity of the thorax and hind limbs. The lung fields appear to be clear, though perhaps mildly decreased in size. There is generalized decreased bone density of the long bones, and both humeri are bowed. There is no foreign body or mass appreciated on evaluation of the coelom.

  

Treatment

He was hospitalized and provided with earthworms overnight after receiving one subcutaneous injection of 8.9 mg calcium gluconate. Treatments during hospitalization included 8.9 mg calcium glubionate PO once daily, 1-2 drops of tobramycin ophthalmic solution applied topically to the skin once daily, and a 10 minute soak in amphibian ringer’s solution once daily (1 part LRS to 2 parts 0.45% saline + 2.5% dextrose). He was sent home the next day with instructions to continue applying 1-2 drops of tobramycin ophthalmic solution once daily topically to the skin for 21 days, 0.09 mL calcium glubionate (2.07 mg elemental calcium) PO once daily for 21 days, 8 mg piperacillin IM once daily for 14 days, and to return for a recheck in 21 days. Recommendations for husbandry were also made and included 10 minutes of supervised exposure to sunlight when temperature permits, using dechlorinated tap water for 25% water changes, removal of pebbles from the tank to decrease bacterial load and the possibility of ingestion, wearing gloves during handling, adding a 10.0 UVB light bulb, and improving his diet by adding earthworms with three times weekly calcium powder dusted on top and a weekly multivitamin.

Follow up

A week after initial presentation, the Green Frog returned for a recheck appointment. Over the week, the generalized edema improved, although the hind limbs continued to remain more swollen than normal. Several days after the frog was sent home, aquarium salt was added to his water, but when a color change of the ventral surface of the frog was noticed, the water was switched to distilled water. In addition, the owners were syringe feeding the frog because he still had a decreased appetite. On examination, the 61 g frog was much improved with regards to the cloacal swelling, the abrasion ventral to his left eye was healing, his left naris was no longer bleeding, and there was only moderate edema of the hind limbs. However, there were multiple areas of the skin that had a gray discoloration with petechiation (ventral abdomen, ventral thighs, lateral carpi) suggestive of chemical burns that were likely due to being soaked in salt water and distilled water. The owners were warned that while the skin may heal with care, it could also potentially become necrotic and slough off. The frog was then sent home with instructions to soak 10-15 minutes once daily in amphibian ringer’s solution for the next two weeks, to syringe feed an insectivore supportive diet as needed, to continue administering the previously prescribed medications, and to return for a recheck in 14 days.  

 

References

Mader, DR. Reptile Medicine and Surgery. 2nd ed. St. Louis: Saunders Elsevier, 2006.

Wright, Kevin M. and Brent R. Whitaker. Amphibian Medicine and Captive Husbandry. Malabar: Krieger Publishing Company, 2001.