from Newly-Identified Influenza D Virus:

Influenza viruses cause seasonal flu each year and pandemics or epidemic sporadically, posing a major threat to public health. Recently, a new influenza D virus (IDV) was isolated from pigs and cattle. Here, we reveal that the IDV utilizes 9-O-acetylated sialic acids as its receptor for virus entry. Then, we determined the crystal structures of hemagglutinin-ester-ase-fusion glycoprotein (HEF) of IDV both in its free form and in complex with the receptor and enzymatic substrate analogs. The IDV HEF shows an extremely similar structural fold as the human-infecting influenza C virus (ICV) HEF. However, IDV HEF has an open recep-tor-binding cavity to accommodate diverse extended glycan moieties. This structural differ-ence provides an explanation for the phenomenon that the IDV has a broad cell tropism. As IDV HEF is structurally and functionally similar to ICV HEF, our findings highlight the poten-tial threat of the virus to public health. Author Summary Of the Orthomyxoviridae family of viruses, influenza A, B and C viruses all can cause dis-ease in humans. Recently, a novel influenza D virus (IDV) with approximately 50 % amin