Eradication of pathogens from mouse colonies is crucial for scientific research reproducibility and animal welfare. The previously described techniques for eradicating pathogens by rederivation through embryo transfer or caesarian technique can be costly and technically challenging. The objective of our study was to assess the efficacy of iodine immersion combined with cross-fostering for eradicating murine norovirus (MNV) and Helicobacter spp. in laboratory mice. The iodine immersion technique was modified to prevent pathogen transmission and reduce the risk of cannibalism. The hypothesis of this study was that iodine immersion combined with cross-fostering of pups would be as effective at eliminating MNV as it is at clearing Helicobacter in laboratory mice. This study was performed on newborn litters of various mice strains housed in a room positive for both these pathogens. The pups were immersed in warmed, diluted iodine within 48 h of birth, and then cross-fostered to a Swiss Webster dam negative for MNV and Helicobacter. The presence of MNV and Helicobacter in donor dams, weanlings, and adult post-immersion animals was tested using fecal PCR. All 27 litters born to MNV- and Helicobacter-positive dams tested negative for both pathogens at weaning and at 8 wk postweaning. Follow-up PCR exhaust dust testing from the housing racks confirmed a negative status for MNV and Helicobacter over multiple quarterly pathogen screening tests conducted over an 18-mo period. This study is, to our knowledge, the first to demonstrate successful eradication of MNV through iodine immersion combined with cross-fostering, proving this method to be effective for eliminating MNV and Helicobacter spp. in affected colonies.
Study plan and timeline. Within 48 h of birth, pups from colonies positive for MNV and Helicobacter were immersed in 50 ppm iodine for 10 s and transferred to a SPF Swiss Webster foster dam. Fecal PCR testing was performed on the dam of the immersed pups and on the fostered pups at weaning and at 8 wk of age. Approximately 1 to 5 mo following immersion, rack-level PCR testing was performed by collecting samples from exhaust plenum. Exhaust dust testing (EDT) was performed triannually at the rack level, which included MNV and Helicobacter.
Iodine immersion setup. The iodine immersion procedure was performed in a biologic safety cabinet. The setup included a cage including the foster SW dam and pups, warmed sterile saline, a thermometer to check the temperature of the diluted iodine, a sterile beaker to contain the diluted iodine for immersion, sterile gauze to place the pups for immersion, a sterile culture dish to collect foster SW pups, and Supreme Mini Treats for nutritional supplementation of the foster dam.
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