Axolotls ( Ambystoma mexicanum ) are critically endangered paedomorphic salamanders with remarkable regenerative capacity. While nearly extinct in the wild, they are commonly maintained in captivity as companion animals, zoological display animals, and biomedical research colonies, where they serve as an animal model for genetics, developmental biology, and regenerative medicine. This report documents a case series of spontaneous myeloid leukemia in genetically related, co-housed adult axolotls in a zoological collection that resulted in 50% overall mortality over 38 months. Affected axolotls exhibited a range of signs, including generalized edema, hydrocoelom, long-term wasting, and sudden death. The most common gross lesions were splenomegaly (5/10) and hepatomegaly (4/10). Microscopically, widespread intravascular neoplasia, consisting of large round cells, was consistently observed (10/10). Neoplastic cells infiltrated and effaced the parenchyma of numerous visceral organs, particularly the spleen and liver. Cytochemical staining of neoplastic cells in blood smears showed strong positive cytoplasmic reactivity for α-naphthyl butyrate esterase and α-chloroacetate esterase and weak staining with periodic-acid Schiff. In tissues, neoplastic cells did not react with Sudan black B and did not express CD3 or ionized calcium-binding adaptor molecule 1 (IBA-1). The morphologic features of the cells and phenotyping tests supported acute myeloid leukemia. This report represents the first documentation of acute myeloid leukemia in caudates.

The American alligator ( Alligator mississippiensis ) is a keystone species of the southeastern United States. In December of 2022, a free-ranging American alligator was found stuporous and tetraparetic. On postmortem evaluation, lesions were limited to the central nervous system, consisting of prominent perivascular cuffs of lymphocytes and histiocytes that extended into the surrounding neuroparenchyma along with gliosis. Next-generation sequencing of the affected brain identified the presence of a piscichuvirus closely related to the freshwater turtle neurovirus 1 (FTuNV-1) recently reported in an alligator snapping turtle with similar microscopic lesions. In situ hybridization using zz-probes that recognize FTuNV-1 identified widespread hybridization signal in neurons and glial cells in the alligator’s brain and spinal cord. This case represents only the second association of piscichuviruses with vertebrate disease. Moreover, it highlights the potential for disease transmission between different orders (Crocodylia and Testudines) of free-ranging aquatic reptiles that share similar habitats in the United States.