H7N9 influenza in China - no human to human transmission - yet!

Wednesday, 10 April, 2013

The number of confirmed cases of H7N9 influenza in easetrn China is now 28 with 9 deaths (case fatality rate of 32%).

No human to human transmission has been proven.

Source: The first genetic analyses of viral isolates from human cases show that the virus's 8 genes have came from 3 sources -- 2 groups of wild bird viruses and one group of H9N2 poultry virus. 6 RNA segments encoding the internal proteins PB1, PB2, PA, NP, M, and NS are derived from H9N2 virus, and the HA and NA from H7N9 virus (Brian Kimble). Virology Blog (http://www.virology.ws/) reports that Brian Kimble notes that the H7N9 isolates possess a L226 equivalent in the HA, which confers human-like receptor binding in other viruses.

An interesting translated report from the Chinese Academy of Sciences suggests the following reassortment scenario:
1. H9N2 avian influenza viruses were found in poultry on the Chinese mainland
2. Korean wild bird carrying H subtypes (including H7N3 and H7N9 subtype avian influenza virus) arrive in the Yangtze River Delta region of China.
3. The Korean virus transmits to Zhejiang ducks with H9N2 and reassort.
4. The new virus transmits to chickens and reassort to produce a new H7N9 subtype.

Note: One H7N9 virus can differ from another H7N9 if the other viral proteins (PB1, PB2, PA, NP, M, NS) are different. Therefore, there can be subtypes of H7N9.

Updated by Rick Speare