Abstract
In 2016, an outbreak of Rattus norvegicus polyomavirus 2 (RatPyV2) infection was reported in a colony of X-linked severe combined immunodeficiency (XSCID) rats in the United States. While RatPyV2 infection persists asymptomatically in immunocompetent rats, immunodeficient XSCID rats develop variable respiratory symptoms, emaciation, impaired breeding performance, and systemic deteriorating condition. RatPyV2 is an epitheliotropic virus targeting epithelial cells of the salivary glands, Harderian glands, extraorbital lacrimal glands, respiratory system, and reproductive or accessory reproductive organs. Histopathologically, the formation of large basophilic nuclear inclusion bodies in the infected epithelial cells is a characteristic feature, along with hyperplasia or dysplasia. Glandular atrophy and loss, accompanied by fibrosis and mononuclear cell infiltration, are also observed in the salivary glands, Harderian glands, and extraocular lacrimal glands. In particular, the parotid salivary glands are prone to be severely and extensively affected with relatively severe and diffuse lesions even at one month of age. Severely affected animals also develop interstitial pneumonia. Among target tissues, the parotid salivary glands appear to be higher susceptible to RatPyV2, therefore pathological examination and PCR examination of the salivary glands, including the parotid salivary glands, are essential for the diagnosis of RatPyV2 infection. This review paper provides a comprehensive summary of the features (clinical signs, pathological findings, and transmission), diagnostic methods, and prevalence of RatPyV2 infection, based on our research and reports from research groups in the United States.This is a secondary publication of "Rat polyomavirus 2 infection" [25] published in JALAS Newsletter (in Japanese) 2021, 70 (1): 17-25. It also includes updated content.