Immunohistochemical analysis for nucleoprotein of avian influenza virus of wood ducks (Aix sponsa) that succumbed to infection (n = 13) with the highly pathogenic avian influenza virus A/whooper swan/Mongolia/244/05 (H5N1)a.

aWood ducks were challenged via choanal cleft with a dose of 104EID50 of A/whooper swan/Mongolia/244/05 (H5N1) 21 days after experimental pre-exposure to different subtypes of low pathogenic avian influenza viruses.bNumbers of immunohistochemically positive cells: + = few; ++ = moderate; +++ = numerous.*Positive immunohistochemical staining associated or not with microscopic lesions.**Positive immunohistochemical staining not associated with microscopic lesions.