A) Developing contour feather. The calamus was used for examination (bar = 1 cm). B) Result of the rapid test with feathers. A pink line (arrowhead) indicates a positive result for influenza A virus. C) Immunohistochemical stain of a biopsied feather composed of feather epidermis (fe) and feather pulp (fp). Influenza virus nucleoprotein was detected in the fe epidermal cells (arrowheads) (bar = 200  m).