Human infections with avian influenza H7N9 virus from wet market poultry

Results of a study of four patients in Zhejiang, China, who developed influenza H7N9 virus infection suggests sporadic poultry-to-human transmission:

We diagnosed avian influenza A H7N9 in all four patients (who were epidemiologically unlinked), two of whom died and two of whom were recovering at the time of writing. All patients had histories of occupational or wet market exposure to poultry. The genes of the H7N9 virus in patient 3’s isolate were phylogenetically clustered with those of the epidemiologically linked wet market chicken H7N9 isolate. These findings suggest sporadic poultry-to-person transmission.

The four patients had occupational contact with poultry: one was a chef, one slaughtered and cooked live market poultry, and two bought live market poultry. Each had contact with poultry 3-8 days before onset of disease, and all were positive for influenza H7N9 virus by polymerase chain reaction of sputum or throat swab samples (virus was cultured from three of the four patients). Two of five pigeons and four of 20 chickens from two different wet markets were also positive for influenza H7N9 virus. Sequence analysis of virus recovered from patient 3 revealed that the HA and NA genes are nearly identical with those of two viruses isolated from epidemiologically linked chickens (1673 of 1683 bases for HA, 1394 of 1398 bases for NA).

While these H7N9 infections might have been acquired from poultry, the origin of other infections in different areas of China (>100) is unclear. According to the Ministry of Agriculture, as of 26 April 2013, only 46 of the 68,060 samples collected from poultry markets, habitats, farms and slaughterhouses across the country have tested positive for H7N9 virus, and none of these positive samples have been from poultry farms.

11 thoughts on “Human infections with avian influenza H7N9 virus from wet market poultry”

  1. Very puzzling. Many of the cases have not had contact with poultry. Maybe there is another source that is not being tested? I say send Ian Lipkin in.

  2. Anyway, the pandemic potential of this new virus is far being established: the actual case-fatality rate, reproduction number and predicted attack rate.

  3. Kathryn Marks

    Please excuse my naive question, but what is the relationship between H9N2 and H7N9?

  4. they reassort frequently (exchange genetic material).
    H9N2 in in Shanghai poultry since > 15 years

  5. There are over 20 million pigs living within a 50km radius where most of the early cases were reported. I looked at the PA gene of H7N9 and while not totally shocking it is similar in many respects to the PA gene of pandemic H1N1, which was derived from the avian lineage TRIG-cassette. So here’s my question…when doing surveillance in swine for H7N9 are they only looking at only HA and NA? Let’s say some of the polymerase or internal H7N9 genes reassort in swine while the HA and NA do not. These internal H7N9 circulate…maybe mutate a little and unknowingly do this for a year or two under our nose with swine HA and NA genes…in a year or two are the conditions right for H7 and N9 either from birds or maybe a human H7N9 isolate that has some additional alpha 2-6 adaptations to then make that important reassortment leap? This is all hypothetical and really just speculation. I would be interested to see which of the 6 genes that are not HA or NA of H7N9 are compatible in swine. Finally what would the replication of the H7 and N9 look like with a TRIG-cassette of swine? It is said that the unique nature of the TRIG-cassette enables a diverse range of HA/NA compatibility.

    I find it a little uneasy that so few H7N9 cases have been found in chickens/wild birds. Gather the eggs, ferrets, MDCK dog cells and mice…off to the lab we go!

  6. This is a very interesting article. I just wonder why most new strains of bird flu viruses came from China? Why not in other Asian countries? I’m just curious. I hope somebody will have a research on this.
    Check this out!

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