Context The ability of influenza A viruses to recognise and bind to cell surface receptors such as sialic acid linked to galactose by an α2,3 linkage (SAα2,3-gal) and sialic acid linked to galactose by an α2,6 linkage (SAα2,6-gal) is a major determinant of influenza A virus infection. Although the epidemiological surveys of influenza A virus infection in raptors suggest that some raptor species are susceptible to influenza A viruses under natural conditions, the sialic acid profiles in the respiratory and intestinal tracts of raptors are unknown. Aims To examine the sialic acid receptor profiles in the respiratory tracts of the selected raptor species and assess the potential susceptibility of raptors to avian and human influenza viruses and the role of raptors in the epidemiology and evolution of influenza A viruses. Methods The lectin immunohistochemistry staining method was used to examine the sialic acid profiles in the respiratory tracts of eight different species of raptors. Key results A strong staining with Maackia amurensis agglutinin (MAA), specific for sialic acid linked to galactose by an α2,3 linkage (SAα2,3-gal), was observed in the epithelial cells of the respiratory tract of Accipiter nisus and Falco tinnunculus. However, a positive staining for both MAA and Sambucus nigra agglutinin (SNA), specific for sialic acid linked to galactose by an α2,6 linkage (SAα2,6-gal), was detected in the epithelial cells of the upper respiratory tract of Accipiter gularis, Buteo buteo, Otus sunia, Bubo bubo and Asio otus, and in the epithelial cells of the alveoli of Buteo buteo, Falco peregrinus, Otus sunia and Bubo bubo. Conclusions Both avian and human influenza A virus receptors are expressed in six species of raptors examined. There are some variations in the type and distribution of sialic acid receptor expression among different raptor species. No correlation between phylogeny of birds and their sialic acid receptor distributions was observed. Implications Since SAα2,3-gal and SAα2,6-gal are often considered as the primary receptors for avian influenza A viruses and human influenza A viruses, respectively, our data suggest that raptors could be a potential host for avian and human influenza A viruses.
Identification of sequence mutations affecting hemagglutinin specificity to sialic acid receptor in influenza A virus subtypes
