A novel video tracking method to evaluate the effect of influenza infection and antiviral treatment on ferret activity.

Ding Yuan Oh,Ian G Barr,Aeron C Hurt,Stephen Mark Tompkins

doi:10.1371/journal.pone.0118780

Abstract

Ferrets are the preferred animal model to assess influenza virus infection, virulence and transmission as they display similar clinical symptoms and pathogenesis to those of humans. Measures of disease severity in the ferret include weight loss, temperature rise, sneezing, viral shedding and reduced activity. To date, the only available method for activity measurement has been the assignment of an arbitrary score by a ‘blind’ observer based on pre-defined responsiveness scale. This manual scoring method is subjective and can be prone to bias. In this study, we described a novel video-tracking methodology for determining activity changes in a ferret model of influenza infection. This method eliminates the various limitations of manual scoring, which include the need for a sole ‘blind’ observer and the requirement to recognise the ‘normal’ activity of ferrets in order to assign relative activity scores. In ferrets infected with an A(H1N1)pdm09 virus, video-tracking was more sensitive than manual scoring in detecting ferret activity changes. Using this video-tracking method, oseltamivir treatment was found to ameliorate the effect of influenza infection on activity in ferret. Oseltamivir treatment of animals was associated with an improvement in clinical symptoms, including reduced inflammatory responses in the upper respiratory tract, lower body weight loss and a smaller rise in body temperature, despite there being no significant reduction in viral shedding. In summary, this novel video-tracking is an easy-to-use, objective and sensitive methodology for measuring ferret activity.

Highlights

Influenza is a highly contagious, respiratory disease that causes high morbidity and mortality worldwide
Prior to measuring the effect of influenza infection on ferret activity, it was important to understand how activity changes over time in non-infected ferrets and to determine the video filming duration that resulted in the highest activity readings with the lowest day-to-day variability
For ferrets that were not treated with oseltamivir, we saw a significant increase in ferret activity on day 1 and a significant decrease in activity on day 6, with activity on all other days being similar to the pre-infection baseline (Fig. 3E)

Summary

Introduction

Influenza is a highly contagious, respiratory disease that causes high morbidity and mortality worldwide. There are many limitations to this methodology of manually scoring ferret activity including potential bias when comparing the effect of a treatment (if the scoring is not conducted in a ‘blinded’ manner), the need for experienced personnel to recognise and assign activity scores relative to the ‘normal’ activity of a ferret, difficulty assessing activity within a small cage, and the broad range of scoring levels which may fail to capture subtle changes in activity Many of these deficiencies can be overcome by the use of EthoVision XT video-tracking software which has been widely-used in studies of neurological and behaviour patterns in experimental animals such as rodents [20] and zebrafish [21]. In addition we used this novel analysis tool to investigate whether treatment with the antiviral drug, oseltamivir of influenza infected ferrets significantly altered their activity levels

Ethics statement

Method Detection sensitivity Subject size

Results

Discussion