Similar transmissibility of the Italian H7N1 highly pathogenic avian influenza virus and its low pathogenic avian influenza virus predecessor.

The transmissibility of the H7N1 highly pathogenic avian influenza virus (HPAIV), which caused a large epidemic in commercial poultry in Italy in 1999-2000, was studied in chickens and compared with that of the low pathogenic precursor virus (LPAIV). Group transmission experiments using the HPAIV were executed to estimate the infectious period (IP), the transmission parameter (β) and the basic reproduction number (R0). These estimates were then compared with those reported for the LPAIV. The estimated β and R0 were similar for both viruses, whilst the IP of the LPAIV was longer than that of the HPAIV. These findings indicate that transmissibility from chicken-to-chicken alone does not appear to confer an advantage for this LPAIV to evolve to a HPAIV.