Update on the new emerging H7N9 bird flu virus in China

Where does the virus come from?

The causative agent is a virus originating in birds. It was created through reassortment - a rearrangement of genes - from different donor viruses.  Its genome contains elements from three different sources: 

• a gene which may come from viruses circulating in domestic ducks in the implicated Chinese provinces;  
• a gene which may come from viruses circulating in wild birds or domestic ducks; 
• genes from viruses which are very often detected in poultry in the provinces implicated in human cases of the virus.

This combination of genes has never before been reported either in birds or in humans. This is also the first time that a virus of the H7N9 subtype has been reported in humans. And finally, this is also the first time that infection by an avian influenza virus that is fatal in humans, but non-virulent in birds, has occurred. 

What is the situation both in China and internationally?

Following the first three cases reported on March 31 in Shanghai and in the Anhui province (west of Shanghai), a total of 132 cases of human infection with the H7N9 virus (including 37 deaths) were reported on May 21. Aside from one case described in Taiwan, but which was imported from China, all the cases were reported in 8 provinces and 2 cities (Shanghai and Beijing). 80% of the cases were concentrated in Shanghai and in the two neighbouring provinces of Zhejiang and Jiangsu (to the south and to the north of Shanghai respectively). 

The cases are generally isolated and no cases of sustained human-to-human transmission have yet been observed.  After a peak during the first half of April, during which nearly half of the cases were reported, the number of cases declined rapidly.

How are humans contaminated?

Due to the avian origin of the emergent H7N9 virus and despite an absence of symptoms in birds, investigations were made in poultry and wild birds.  The geographical area in which the virus was detected in birds overlaps with the provinces affected by human cases, except for in the province of Guangdong (southern China, near Hong Kong) which has not yet reported any human cases. No positive samples have been found in farms, which suggests that poultry are infected after leaving the farms, during transport to various resellers and/or in live poultry markets. 

An OIE expert mission organised in connection with WHO and FAO in April concluded that live poultry markets played a key role in infection of both humans and poultry by the H7N9 virus. This hypothesis seems to be confirmed by the fact that there was an abrupt cessation of new cases following the closing of live poultry markets.  

However, genetic analysis of the virus has shown that it presents mammalian adaptation markers, which explains the cases observed and raises concerns of the virus's having evolved to facilitate airborne transmission from human to human. Other potential sources of human contamination are still being looked into.

What is ANSES doing with regard to the H7N9 virus? 

Since the first cases were announced, ANSES has set up, in conjunction with the French Institute for Public Health Surveillance (InVS), a daily international watch scheme and issues weekly updates on the situation. In addition, since the first cases, the National Reference Laboratory for avian influenza (ANSES Ploufragan Laboratory) immediately verified the validity of the detection and characterisation tools it already had in its possession, together with the international network of OIE/FAO reference laboratories, and informed the approved diagnostic laboratories for the detection of avian influenza viruses. The laboratory is ready to contribute to all the investigations which are deemed necessary.