Fig. 1.

[colour online]. Schematic illustration of the design of transmission experiments conducted in this study. Experiments with H5N2 A/Ch/Belgium/150VB/99 and H7N1 A/Ch/Italy/1067/v99 comprised two separately conducted trials. The experiment with H5N3 A/Anas platyrhynchos/Belgium/09-884/2008 comprised only one trial. Each trial included two subtrials which were simultaneously conducted in different isolators; in one isolator, animals were housed on a grid floor; in the other isolator the floor was covered with litter. In each isolator, six seeders (red diamonds) and six contacts (green ovals) were housed.