Cases/Abstracts

Snake with a unique parasite-induced malignancy.

Heather Sayles1, Scott D. Fitzgerald, DVM, Dipl ACVP, Dipl ACPV1, and Mayra F. Tsoi, DMV, PhD, Dipl ACVP1

1- Michigan State University College of Veterinary Medicine, East Lansing, MI, 48824, USA

SIGNALMENT:

2-month-old female intact black-headed cat snake (Boiga nigriceps)

HISTORY:

A juvenile black-headed cat snake that was being treated for strongyloides and skin mites was found dead in its enclosure. The animal was kept in quarantine.

GROSS FINDINGS: 

Caudal coelom: Numerous intracoeleomic nematodes along with numerous cysts on the serosa and connective tissue. Large amount of intracoelomic mucus and petechiation in the coelomic fat bodies.

HISTOPATHOLOGIC AND CLINICAL PATHOLOGY FINDINGS: 

Scattered throughout the gastrointestinal tract, oviduct, and kidney were approximately one dozen, 1.5 mm to 2.8mm in diameter, well demarcated nodules consisting of densely cellular, atypical spindle cells forming tight interlacing fascicles. Spindle cells had a small amount of eosinophilic cytoplasm, indistinct cell borders, and ovoid nuclei with finely stippled chromatin and 0-1 prominent nucleoli. Anisokaryosis was mild to moderate and there were no mitoses in 10 high power fields (2.37mm2). Several of these nodules contained encysted nematodes, characterized by a width of 0.25 mm, a pseudocoelom, a digestive tract, lateral chords, and paired lateral alae. Nodules were most often arising from the serosal surface of visceral organs, invading into the muscularis, or arising just below the capsule (kidney). 

MORPHOLOGICAL/ETIOLOGICAL DIAGNOSIS:

Disseminated sarcomas with encysted nematodes

DISCUSSION:

Nematode-induced tumor formation has been theorized in dogs, cats, ruminants, rodents, pheasants, muskrats and primates1. The nematode with the strongest link to the formation of malignant lesions in veterinary species is Spirocera lupi, the causative agent of spirocercosis2. S. lupi completes its development in the submucosa and the subadventitia of the esophagus, where its presence leads to chronic inflammation and the formation of fibrous nodules or benign granulomas2. In approximately 25% of infected animals, esophageal nodules undergo neoplastic transformation to malignant sarcomas that can metastasize to other organs2. However, this parasite primarily infects dogs and wild carnivores, and no reports have identified spirocercosis in any reptilian species to date. 

Gastrointestinal parasitism is relatively common in snakes. The most common gastrointestinal parasites found in snakes (Ophiotaenia spp., Rhabdias spp., Strongyloides spp., Ophidascaris spp., Eustrongylides spp., Ascaridia spp., and Kalicephalus spp.) are capable of inducing the formation of benign granulomas. In a 2007 case report, multiple granulomatous lesions were found in several organs of a free-ranging adult dice snake likely induced by Eustrongylides larvae3. While there are certainly parallels to be drawn between the dice snake and the juvenile cat snake in this case, the parasite-induced lesions in the juvenile cat snake were not consistent with benign granulomas. The dense cellularity and invasiveness of spindle cells was most consistent with a diagnosis of sarcoma. To the author’s knowledge, there has only been one report suggestive of parasite-induced tumor formation in snakes1. In that report, Ophidascaris spp. was identified inside necrotic areas of a gastric adenocarcinoma in a 7-year-old diamond python4. However, it was unclear as to whether the parasitic infection in that diamond python could have been independent of the adenocarcinoma formation. 

In this case, the presence of multiple cross sections of nematodes surrounded by neoplastic cells forming multifocal nodules is highly suggestive of a link between the nematode and neoplastic transformation of mesenchymal cells. The identification of this nematode was attempted by PCR; unfortunately, there was insufficient DNA in the formalin-fixed, paraffin-embedded sample for identification. 

REFERENCES: 

1. Fonti, N., Parisi, F., Mancianti, F., Freer, G., & Poli, A. (2023, July 26). Cancerogenic parasites in veterinary medicine: A narrative literature review. Infectious agents and cancer. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10373346/ 

2. Rojas, A., Dvir, E., & Baneth, G. (2019, November 13). Insights on Spirocerca Lupi, the carcinogenic dog nematode. Insights on Spirocerca lupi, the Carcinogenic Dog Nematode. https://www.sciencedirect.com/science/article/abs/pii/S1471492219302466 

3. Mihalca, A. D., Fictum, P., Škorič, M., Sloboda, M., Kärvemo, S., Ghirra, I., Carlsson, M., & Modrý, D. (2007, January). Severe granulomatous lesions in several organs from eustrongylides larvae in a free-ranging dice snake, Natrix tessellata. Severe Granulomatous Lesions in Several Organs from Eustrongylides Larvae in a Free-ranging Dice Snake, Natrix tessellata. https://pubmed.ncbi.nlm.nih.gov/17197633/ 

4. Baron, H. R., Šlapeta, J., Donahoe, S. L., Doneley, R., & Phalen, D. N. (2018, December). Compensatory gastric stretching following subtotal gastric resection due to gastric adenocarcinoma in a diamond python (Morelia spilota spilota). Australian veterinary journal. https://pubmed.ncbi.nlm.nih.gov/30478847/