Abstract

Reports of lymphoma or lymphosarcoma with or without lymphoid leukemia are becoming common in the reptile literature.^{2-5,7,11,14,16} The vast majority of these reports consist primarily of necropsy and histopathologic findings. Increasingly however, treatment modalities are being attempted for reptile neoplasias.^{1,9,10,12,13,15} This report describes an attempt at chemotherapy for lymphoma in a king cobra (Ophiophagus hannah) at the Gladys Porter Zoo.

In November 1996, a captive-born, 2.8-m, adult, 2.0-kg, female cobra was presented for a chronic wound of the right thoracic area. Previous history included one fecal sample positive for strongyles and a mild dystocia in 1991. A keeper recalled that the snake was bitten in that area by a Philippine crocodile (Crocodylus novaeguineae mindorensis) approximately 6 mo earlier, and that the wound never healed.

A physical examination was performed using manual restraint. The wound was located 30 cm distal to the head and appeared pink, oblong (2.5x5.0 cm), roughly marginated, and non-scaled. It moved easily with the skin and did not appear to be associated with any deeper structures. The tissue was very friable but did not appear necrotic. The ventral scutes at that area also seemed abnormal, appearing involuted. A blood sample was obtained via cardiocentesis and a full-thickness punch biopsy of the site was taken. Differential diagnoses included granulation tissue or a neoplastic process.

Hematology indicated leukocytosis and a lymphocytosis; lymphocytes composed 88% of the total white blood cell count (Table 1). The only abnormality on the plasma biochemistry was hyperglobulinemia (5.1 g/dl; normal value: 3.9 g/dl).⁶ The biopsy result indicated severe, granulomatous cellulitis with atypical lymphocytes. The atypical lymphocytes suggested a preneoplastic change and a wide surgical excision of the lesion was recommended.

In December 1996, the snake was intubated using manual restraint and anesthetized with isoflurane (Aerrane, Fort Dodge, Overland Park, KS, USA) for surgical removal of the mass. By February 1997, the surgical site was well healed, the sutures were removed, and the snake was eating well on its own.

Table 1. Chemotherapy protocol and response to treatment of lymphoma in a king cobra (Ophiophagus hannah) at the Gladys Porter Zoo

^aAnimal calculated to be 0.2 m².
^bWhite blood cell count; ISIS normal=7.614±6.993 x 10³/µl.^6
cISIS normal=4.063±5.515 x 10³/µl.^6
dAdministered intracardiac.
^eTreatment.

By April 1997, the mass had returned at the primary site, with a second lesion present at the site of the involuted ventral scutes identified in November 1996. At both sites, the surrounding scales appeared edematous and exuded clear, serous liquid. Samples were collected for hematology, plasma biochemistry, fluid cytology, bacterial culture, and histology.

Abnormalities on hematology and plasma biochemistry included leukocytosis and lymphocytosis along with an increased total solids (9.0 mg/dl; normal value: 5.7 mg/dl) and hyperglycemia (108 mg/dl; normal value: 58 mg/dl).⁶ Cytology of the fluid from the lesions indicated a secondary bacterial infection, and coagulase-negative Staphylococcus sp. and Acinetobacter calcoaceticus were identified from the culture of the lesions. The biopsy results indicated lymphosarcoma at both sites. The snake was placed on amikacin (Amiglyde-V, Fort Dodge, Overland Park, KS, USA) at 2.5 mg/kg SC q 72 h for five treatments, concurrent fluid administration (two parts 2.5% dextrose in 0.45% NaCl and one part Ringer’s) at 25 ml/kg SC q 72 h, and the masses were cleaned with dilute chlorhexidine (Vedco, Incorporated, St. Joseph, MO, USA) q 72 h.

In May 1997, the snake was again anesthetized with isoflurane and both masses were surgically excised. This surgery resulted in extensive tissue loss, down to the level of the peritoneum on the ventral aspect of the site, and the ribs were compressed ventrally with suture to provide protection for the coelomic cavity. The surgical site was dressed with DuoDERM (Bristol-Myers Squibb, Company [ConvaTec], Princeton, NJ, USA), wrapped with petrolatum gauze (Sherwood Medical, St. Louis, MO, USA), and covered with Tegaderm (3-M, St. Paul, MN, USA). The petrolatum gauze kept the wound moist as well as inhibited the snake from “crawling out” of its bandage. The snake was started on enrofloxacin (Baytril, Bayer Corporation, Shawnee Mission, KS, USA) at 10 mg/kg SC q 24 h for 10 treatments. By June 1997, the snake had shed and was eating well; the surgical site continued to heal slowly. However, by July 1997, the masses regrew at both surgical sites.

In August 1997, the two original surgical sites were still being dressed and two new skin lesions appeared, one 60 cm distal to the head on the left side, and one 17 cm cranial to the vent on the left side. A chemotherapy regimen was instituted using L-asparagine aminohydrolase (FloridaInfusion, Palm Harbor, FL, USA), vincristine (FloridaInfusion), and prednisone (Meticorten, Schering-Plough Animal Health, Union, NJ, USA) (Table 1). Periodic hematology and plasma biochemistry, and size and appearance of the skin lesions were used to monitor the efficacy of the chemotherapy protocol.

The snake tolerated handling and administration of drugs reasonably well but generally required forced feeding. Clinical impressions by the keeper staff were that the snake was more aggressive than usual, seemed hungry but did not want to eat, had lighter overall skin color, occasionally made uncoordinated movements, was possibly in pain as it was more likely to bite than hood, and had poor muscle tone.

Within 1 wk, the skin lesions appeared to respond to the chemotherapy, becoming smaller and less “angry” looking, with areas of necrosis. Hematology parameters showed a decrease in the total white blood cell count, lymphocyte count, and the percentage of lymphocytes (Table 1). In addition, other changes in the hematology and plasma biochemistry included a decrease in packed cell volume (16%; normal value: 28.7%), hyperglycemia (110 mg/dl; normal value: 58 mg/dl), hypoproteinemia (4.3 g/dl; normal value: 6.8 g/dl), and hypoalbuminemia (1.5 g/dl; normal value: 2.8 g/dl).⁶

Because the lesions were not regressing as anticipated, a second round of chemotherapy was initiated in early September 1997 (Table 1). But by the end of September 1997, the tumors had once again begun to grow and metastasize to new sites on the body. The snake developed ventral edema and was started on enrofloxacin at the previous dose. The chemotherapy regime was discontinued.

In October 1997, the snake was having trouble shedding and had many unhealthy areas of skin on its body; however, its attitude and appetite were excellent. At this time, a different chemotherapeutic regimen (Table 1) was initiated using prednisone and chlorambucil (FloridaInfusion). By November 1997, the lesions had not progressed but the snake was again being force fed. By December 1997, the lesions were once again growing. The snake was found dead on 8 February 1998, 15 mo after presentation.

At necropsy, the snake weighed 1.6 kg and was in poor body condition. There were four cutaneous lesions as previously described, with the original two sites coalescing into a single mass. The thymus was grossly enlarged (11x3 cm) and there were several vertebral swellings noted. Samples of tissues were collected in 10% buffered formalin and submitted for histopathology. Histopathologic lesions included multicentric, intermediate to high grade lymphoma involving most of the visceral organs and bone marrow. Appreciable treatment effect could not be confirmed. In addition, there was mild gastroenteritis, mild glomerulosclerosis of the kidney, moderate atrophy of the fat bodies, and moderate, degenerative osteoarthritis of the vertebrae. Thymus prepared for electron microscopy failed to demonstrate any viral structures; no virus was isolated from thymus tissue passaged on viper heart cell line.^8,17,19 Additional efforts to further characterize the lymphoma are ongoing.¹⁸

Acknowledgments

We thank Claudia Barton, DVM, Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, Texas A&M University, College Station, TX for her assistance in designing the oncologic treatment protocol, and the Gladys Porter Zoo Herpetarium staff for their expertise in handling and caring for this individual.

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