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Published reports of spontaneous neoplasia in marsh rice rats (Oryzomys palustris) are sparse. We report here a case of cutaneous epitheliotropic T-cell lymphoma in a 14-mo-old marsh rice rat that involved the ear pinnae, with dissemination to the liver and spleen. Histologically, the thickened ear pinnae showed diffuse infiltration of neoplastic lymphocytes into the epidermis, dermis, and adnexal skin structures, with Pautrier microaggregations present in the epidermis. In addition, neoplastic lymphocytes were observed infiltrating and disrupting the architecture of the liver and spleen. Neoplastic lymphocytes were strongly positive for the T-cell marker CD3 but were negative for the B-cell markers CD19 and CD20. These histologic and immunohistochemical features are consistent with an epitheliotropic T-cell lymphoma, as previously reported in other species, including humans. To our knowledge, this report represents the first published case of spontaneous cutaneous epitheliotropic T-cell lymphoma in a marsh rice rat.

Rice rats (Oryzomys palustris) are a recognized animal model for studying periodontal disease and the photoperiodic regulation of reproduction. Here we share information regarding the breeding, husbandry, veterinary care, and hematologic findings about this animal species to facilitate its use in studies at other research institutions. Rice rats initially were quarantined and monitored for excluded pathogens by using microbiologic, parasitologic, and serologic methods with adult female Mus musculus and Rattus norvegicus sentinel animals. Breeders were paired in a monogamous, continuous-breeding system. Rats were housed in static filter-top cages, maintained on commercial chow under 14:10-h light:dark cycles at 68 to 79 °F (20.0 to 26.1 °C) and 30% to 70% humidity. Rice rats apparently adapt relatively well to standard laboratory conditions, despite their aggressive behavior toward conspecifics and humans. Our analysis of 97 litters revealed that dams gave birth to an average of 5.2 pups per dam and weaned 4.2 pups per dam. Several procedures and biologic reagents normally used in standard laboratory rodents (mice and rats) can be used with rice rats. In addition, we present hematologic and serum chemistry values that can be used as preliminary reference values for future studies involving rice rats.