Clinical, Gross, and Histopathologic Findings in a Cluster of Six Cases of Malignant Peripheral Nerve Sheath Tumors in Senegal Bichirs (Polypterus senegalensis)
Alisa L. Newton, VMD, DACVP; Kate A. Gustavsen, PhD, DVM; Jean A. Paré, DMV, DVSc, DACZM; Denise McAloose, VMD, DACVP
Bichirs (Polypterus spp.) are evolutionarily ancient freshwater fish native to central Africa. They are popular exhibit fish due to their strikingly primitive appearance and retained physiologic characteristics, including obligate air-breathing with true lungs.2 From 2011 through 2014, six of 19 adult Senegal bichirs (Polypterus senegalensis) in the Wildlife Conservation Society collection developed large, disfiguring tumors resulting in death or euthanasia. Tumors were located in the musculature of the dorsal or lateral body wall. The most advanced cases ruptured through the skin, exposing an exophytic, broad-based mass that was not amenable to resection. Observed clinical signs were limited to mildly decreased activity, though at necropsy some fish were in thin condition and most had empty digestive tracts. Necropsy findings included a second, earlier stage tumor in two cases, coelomic invasion in one case, and metastatic disease in one case. Histologically, these neoplasms were infiltrative into the epaxial muscles, and in one case invaded and effaced vertebrae. One fish had evidence of secondary bacterial sepsis. The histologic diagnosis in each case was malignant peripheral nerve sheath tumor or neurofibrosarcoma; tumor locations suggested an origin from the spinal nerves. Similar tumors occur spontaneously in a number of fish species, and an infectious etiology has been demonstrated in epizootic peripheral nerve sheath tumors of bicolor damselfish (Stegastes partitus).1,3 The high prevalence of the same neoplasm in this bichir colony is suggestive of an infectious etiology, though an agent has not yet been identified.
The authors acknowledge Dr. Carlos Rodriguez for his gross necropsy contribution to one of these cases.
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