On April 21, 2008, four whooper swans were found dead at Lake Towada, Akita prefecture, Japan. Highly pathogenic avian influenza virus of the H5N1 subtype was isolated from specimens of the affected birds. The hemagglutinin (HA) gene of the isolate belongs to clade 2.3.2 in the HA phylogenetic tree.

Mammalian melanoma differentiation-associated gene-5 (MDA5) and retinoic acid-inducible gene-I (RIG-I) selectively sense double-stranded RNA (dsRNA) according to length, as well as various RNA viruses to induce an antiviral response. RIG-I, which plays a predominant role in the induction of antiviral responses against influenza virus infection, has been considered to be lacking in chicken, putting the function of chicken MDA5 (chMDA5) under the spotlight. Here, we show that chMDA5, unlike mammalian MDA5, preferentially senses shorter dsRNA synthetic analogues, poly(I:C), in chicken DF-1 fibroblasts. A requirement for caspase activation and recruitment domains for chMDA5-mediated chicken interferon beta (chIFNβ) induction and its interaction with mitochondrial antiviral signaling proteins were demonstrated. We also found that chMDA5 is involved in chIFNβ induction against avian influenza virus infection. Our findings imply that chMDA5 compensates in part the function of RIG-I in chicken, and highlights the importance of chMDA5 in the innate immune response in chicken.

Background  Recent studies have revealed the existence of genetic diversity in swine influenza viruses (SIVs) in the world. In Thailand, there has been a little information on the molecular characteristics of the SIVs since the first isolation of viruses of H1N1 and H3N2 subtypes in the late 1970s. Our previous study demonstrated that Thai H1N1 SIVs possessed the classical swine H1 and avian‐like swine N1 genes (Takemae et al., Proceedings of the Options for the Control of Influenza VI.2007;350–353).Objectives  In the present study, we genetically characterized 12 SIVs including those of H1N1, H1N2 and H3N2 subtypes isolated between 2000 and 2005.Methods  We determined the entire nucleotide sequences of the eight gene segments of those isolates.Results  Phylogenetic analysis revealed the existence of nine distinct genotypes amongst the Thai SIVs. These genotypes arose from multiple introductions of classical swine, avian‐like swine and human viruses. The existence of two distinct sublineages within classical swine H1 and NS, avian‐like swine PA and M and human H3 and N2 genes of the Thai SIVs suggested that introduction of viruses of classical swine, avian‐like swine and human origins occurred twice respectively into the Thai pig population. The predominance of avian‐like swine genes amongst the Thai SIVs was evident. In particular, three polymerase (PB1, PB2 and PA) and matrix genes of avian‐like swine origin were retained in all the Thai SIVs examined.Conclusions  These observations may suggest that genes of avian‐like swine lineages have some advantages to be maintained in pigs as seen in the SIVs established through multiple introductions in other regions.