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Open Access Effects of Pelleting, Irradiation, and Autoclaving of Rodent Feed on MPV and MNV Infectivity

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Murine norovirus (MNV) and mouse parvovirus (MPV) are among the most common adventitial viruses seen in laboratory mice, and infections arise in barrier facilities despite rigorous biosecurity programs. Some authors have implicated nonsterilized feed as a source of MPV in rodent facilities, but none have conclusively documented viral particles in the feed. In this study, we hypothesized that both viruses can resist the pelleting process but not subsequent irradiation or autoclaving, thus revealing a potential source of outbreaks in rodent facilities. To test this hypothesis, we contaminated powdered feed with 10-fold concentrations of MNV and MPV and fed it to both Swiss Webster (SW) and C57BL/6NTac (B6) mice to determine a 'powdered ID50' according to seroconversion over a 28-d period. We repeated the experiment by using powdered feed that we contaminated with increasing viral doses (as no. of powdered ID50) and subsequently pelleted; from these results, we determined a 'pelleted ID50.' Finally we assessed the effect of irradiation and autoclaving on contaminated pellets by using the same experimental design. The powdered ID50 was relatively low and identical in both mouse strains (2.51 × 102 pfu) for MNV but higher in B6 (copy number, 3.20 × 106) than SW (3.98 × 104 copies) for MPV. As hypothesized, mice were infected by contaminated rodent feed despite the pelleting process. Indeed, pelleting resulted in a 1- to 2-log increase in ID50 in both strains for MNV and MPV. Irradiation and autoclaving of infected pellets effectively prevented seroconversion of mice exposed to all doses of MNV, whereas a single mouse seroconverted at the highest dose of MPV (1.35 × 107 copies). These data suggest that both MNV and MPV remain infectious after conditions reproducing the rodent chow pelleting process and that nonsterilized rodent chow might be a source of viral outbreaks.
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Document Type: Research Article

Affiliations: 1: Animal Resources Department, The Salk Institute for Biological Studies, La Jolla, California 2: IDEXX BioAnalytics, Columbia, Missouri 3: PMI Nutrition International, LabDiet, St Louis, Missouri 4: Office of Animal Resources, University of Colorado–Boulder, Boulder, Colorado 5: Animal Resources Department, The Salk Institute for Biological Studies, La Jolla, California;, Email: [email protected]

Publication date: September 1, 2019

This article was made available online on August 7, 2019 as a Fast Track article with title: "Effects of Pelleting, Irradiation, and Autoclaving of Rodent Feed on MPV and MNV Infectivity".

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  • The Journal of the American Association for Laboratory Animal Science (JAALAS) serves as an official communication vehicle for the American Association for Laboratory Animal Science (AALAS). The journal includes a section of refereed articles and a section of AALAS association news. The mission of the refereed section of the journal is to disseminate high-quality, peer-reviewed information on animal biology, technology, facility operations, management, and compliance as relevant to the AALAS membership. JAALAS accepts research reports (data-based) or scholarly reports (literature-based), with the caveat that all articles, including solicited manuscripts, must include appropriate references and must undergo peer review.

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