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Abstract
The year 2014 was marked by one of the worst outbreaks of highly pathogenic avian influenza (HPAIV) in the United States, which led to culling of millions of poultry species. Introduction of this novel clade 2.3.4.4 of H5 viruses, was linked to the intercontinental movement of migratory birds. These viruses are unique firstly, by causing death in both gallinaceous poultry and wild birds, and secondly, because, of an apparent age-associated predisposition to infection during outbreaks.To investigate these differences, recombinant hemagglutinin glycoproteins (rHA)s were generated from a highly pathogenic H5N2 virus from the clade 2.3.4.4, A/Northern pintail/Washington/40964/2014, a low pathogenic H5N2 virus, A/mallard/MN/410/2000. The rHAs were used in protein histochemistry studies of the respiratory tract, intestinal tract and cloacal bursa. HA binding was then correlated to median area of binding (MAB) scores. In the first project, birds of the orders Anseriformes, Charadriiformes, Accipitriformes, Columbiformes and Galliformes were evaluated. The HPAIV rHA had tropism to the respiratory tract of various domestic and wild birds, and intestinal tract tropism to some Anseriformes and Galliformes. The LPAIV rHA had strong respiratory tract tropism only in Mallard ducks and turkeys. Overall, it was found that the clade 2.3.4.4 H5 HA had a wider host range compared to the LPAIV H5 HA, which is reflective of reported field and laboratory studies.Next, the effect of age on the tissue tropism was evaluated in birds of the taxonomical orders Anseriformes and Galliformes using the same HPAIV and LPAIV rHA. With the HPAIV, an age-associated rHA binding was seen, with younger Mallard ducks and Muscovy ducks having higher respiratory MAB scores, while younger Mallard ducks and chickens had the highest HPAIV intestinal MAB scores. Using the LPAIV, older birds (layer chickens, Pekin ducks and turkeys) had the highest respiratory MAB scores. Overall, age-related differences in MAB and tissue tropism was determined in some species which aids in explaining some age-associated differences in host susceptibility. The differences in tropism were also dependent on the virus used. The collective findings of these studies aid in improving understanding of the pathobiology of avian influenza virus infection in avian species.