WHO: Human infection with avian influenza A(H7N9) virus - China(Mutation, Risk accessment)

On 18 February 2017, the National Health and Family Planning Commission of China (NHFPC) reported to WHO the results of genetic sequencing on virus isolates from two previously reported cases of human infection with avian influenza A(H7N9) virus from Guangdong province. Changes at the cleavage site of the HA gene suggestive of being highly pathogenic to poultry was confirmed by the Chinese National Influenza Centre of the Chinese Centre for Disease Control and Prevention (China CDC).

Details of the cases

The two cases were reported through International Health Regulations (IHR) notification on 19 January 2017.

Investigation revealed exposure to sick and dead poultry. None of the 105 close contacts of these two cases developed symptoms during the two weeks of medical observation. To date, there is no evidence of changes in pathogenicity to and transmissibility among humans.

Public health response

Considering the new developments in H7N9 genetic sequence, the Chinese government is implementing additional measures in Guangdong province on top of current existing measures:

WHO risk assessment

This is the first report of avian influenza A(H7N9) virus, since its emergence in 2013, having genetic sequences that are suggestive of evolving from a low pathogenic into a highly pathogenic avian virus. Similar changes at the cleavage site of the HA gene were also found in genetic sequence data uploaded in Global Initiative on Sharing Avian Influenza Data (GISAID) of a virus from a recent human case reported by Taiwan, China earlier to WHO on 4 February 2017 with travel history to Guangdong. In addition the Ministry of Agriculture China reported to World Organisation for Animal Health (OIE) on 21 February 2017 that genetic sequences of virus samples from live poultry markets in Guangdong also showed changes consistent with highly pathogenic avian influenza viruses. So far the above genetic changes have been found in viruses from human, poultry and environmental samples from Guangdong or with travel history to Guangdong province.

In addition the genetic sequences from the two human cases from Guangdong and the case reported by Taiwan, China showed amino acid substitutions associated with neuraminidase inhibitor antiviral drug resistance. It was reported that the three patients received antiviral treatment before samples were taken.

So far there is no evidence of change of epidemiological patterns of avian influenza A(H7N9) infection in humans. There is no evidence that a change in the virus from low pathogenic to high pathogenic avian influenza virus has an impact on the pathogenicity or transmissibility in humans.

Overall the likelihood of further community level spread remains low.

WHO is closely monitoring the impact of these viruses on public health through its Global Influenza Surveillance and Research System (GISRS) network, and its effect on animal health through collaboration with Food and Agriculture Organization of the United Nations (FAO) and OIE, and will update public health risk assessment accordingly.

A change in the virus from low pathogenicity to highly pathogenicity in poultry may have implications on surveillance and control strategies at the animal sector.

WHO advice

WHO advises that travellers to countries with known outbreaks of avian influenza should avoid, if possible, poultry farms, contact with animals in live poultry markets, entering areas where poultry may be slaughtered, or contact with any surfaces that appear to be contaminated with faeces from poultry or other animals. Travellers should also wash their hands often with soap and water, and follow good food safety and good food hygiene practices.

WHO does not advise special screening at points of entry with regard to this event, nor does it currently recommend any travel or trade restrictions. As always, a diagnosis of infection with an avian influenza virus should be considered in individuals who develop severe acute respiratory symptoms while travelling in or soon after returning from an area where avian influenza is a concern.

WHO encourages countries to continue strengthening influenza surveillance, including surveillance for severe acute respiratory infections (SARI) and influenza-like illness (ILI) and to carefully review any unusual patterns, ensure reporting of human infections under the IHR 2005, and continue national health preparedness actions.