Discussion
Automated activity monitoring of laboratory animals may provide an objective measure to follow disease progression following infection with respiratory viruses. Here we tested a system using RFID transponders to follow the activity of individual mice challenged with mouse-adapted Influenza A/PR8 virus. We noted a decline in activity, which correlated with weight loss. In contrast, vaccination prevented this decline in activity. A similar decline in activity was observed in previous studies using computerized home cage monitoring (HCM) to measure average group activity of mice in the context of SARS-CoV-2 and influenza virus infection5,6.
Automated activity monitoring presents a number of advantages over more subjective symptom scoring, which is typically performed by animal research technicians. By following the mice in their familiar environment and minimizing animal-human interactions, automated activity monitoring may cause less stress to the animals and has the potential to improve the data quality by offering an objective assessment. Furthermore, automated monitoring, could give less data variation, which may allow for reductions in the number of animals used to test the protective efficacy of vaccines7. Notably, using automated monitoring of activity, we found that reduced activity preceded weight loss. An advantage of the RFID transponder system used in our studies is the ability to monitor mice at an individual level. Activity monitoring may therefore be used to inform animal caretakers to follow specific animals more closely and could potentially serve as endpoint in murine challenge studies. As an objective measure of animal health status, activity monitoring could thus be used to improve animal welfare by alerting animal caretakers upon a sudden decline in activity.
In summary, the use of automated activity monitors could present significant advantages for data accuracy and animal welfare and is increasingly used in preclinical research8-10. By providing continuous and objective monitoring, automated activity monitors may also be implemented for respiratory virus challenge models and vaccine testing. Here we tested their use in influenza vaccine studies and demonstrate that mice immunized with HA protein formulated in CAF01 retained their activity following challenge. The data demonstrate the promise of using automated activity monitors for challenge studies with influenza and possibly other respiratory viruses.