Image 1 (IMAGE) The University of Hong Kong Caption The European avian-like (EA) H1N1 swine influenza virus was derived from an avian influenza virus through interspecies jump that occurred prior to 1979. The EA swine influenza viruses have been established in pig herds in European and Asian countries since 1979. The EA swine viruses donated the neuraminidase (NA) and M gene segments to the A(H1N1)pdm09 virus that caused the 2009 influenza pandemic. In this study, Su et al. investigated the molecular changes facilitated the avian-to-pig adaptation of the EA swine influenza viruses. Ancestral sequence reconstruction was used to gain viruses representing different adaptive stages of the EA swine influenza virus as it transitioned from avian to swine hosts since 1979. A key parameter for virus adaptation in a new host is its transmissibility.Transmissibility is assessed by counting the proportion of contact piglets (N=4) that become infected after co-housing with infected donor pigs in the same cage, a condition that allows all major modes of transmission to occur. The research team found that the EA swine influenza viruses acquired amino acid changes in the viral polymerase (PB1-Q621R) and nucleoprotein (NP-R351K) that facilitated efficient pig-to-pig transmissibility after 1983. The results suggest a potential window for intervention (1979-1983) before the virus is fully adapted in pigs. Credit The University of Hong Kong Usage Restrictions This work is licensed for non-commercial, non-exclusive, one-time usage with attribution to the copyright holder. License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.