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Weekly Overview: H7N9 Influenza in China

11 April 2013

ANALYSIS - The influenza A virus that has so far caused 28 confirmed human infection in eastern China is caused by the H7N9 subtype. It is thought to be the result of a genetic reassortment of viruses from wild birds and poultry in the region. The source of infection is not yet known but it does not appear to be poultry although it has been found in chickens and ducks at live markets in the area. Turning to foodborne disease incidence in the EU, campylobacteriosis cases are increasing while the decline in salmonellosis continues. The new WASDE report has been published.

According to its latest report, dated 10 April, the World Health Organization (WHO) says a total of 28 human cases have been confirmed with influenza A(H7N9) virus in China, including nine deaths, 14 severe cases and five mild cases. The first known case was reported in early March, and all cases so far have been located in eastern China.

With the common flu symptoms of respiratory problems and pneumonia, the authorities are monitoring the situation closely. It appeared at first that the infection could not be passed from person to person but WHO's latest report states that in Jiangsu, investigation is ongoing into a contact of an earlier confirmed case who has developed symptoms of illness. The possibility of the virus being transmitted between humans cannot be ruled out, a WHO official has said.

Chinese officials have expressed confidence in curbing the H7N9 strain of bird flu, stating how the country has built capacity to deal with epidemics since the SARS outbreak.

The term 'bird flu' is much used in the media in respect of the current outbreak. In fact, birds (including poultry) may not be the direct source of infection in this latest outbreak; most of the victims did not have contact with poultry.

The link with birds is based on the fact that influenza A viruses of the H7 type are normally found in avian species. They have caused illness in humans in western countries in the past - but rarely and not in China.

A Chinese laboratory has described the H7N9 avian influenza as the result of a genetic reassortment of viruses from wild birds in East Asia with those from chickens in East China.

One feature of this outbreak that makes it different from H5N1 - which has been circulating since 2003 and is known to have infected 622 people - is that the H7N9 sub-type is a low-pathogenic form in poultry. H5N1 is highly pathogenic to most domestic poultry and most affected birds die suddenly. This low-pathogenic H7N9 form does not kill the birds and indeed, may only be identified by testing.

A veterinary expert in China said this week that H7N9 bird flu has not triggered an epidemic among poultry. However, the veterinary authority there has reported finding the virus in chickens and ducks at five live bird markets in Anhui, Zhejiang and Jiangsu - the regions with human cases. In Nanjing, live poultry markets have been closed.

Also in the news this week, grain futures markets have come under modest selling pressure in the wake of the latest USDA monthly supply and demand report (WASDE).

Campylobacteriosis is the most reported zoonotic disease in humans, with a continuous increase in reported cases over the last five years, according to the annual report on zoonoses and food-borne outbreaks in the European Union.

The joint report from European Food Safety Authority (EFSA) and the European Centre for Disease Prevention and Control (ECDC) says that the trend in reported human cases of verocytotoxin-producing Escherichia coli (VTEC/STEC) has also been increasing since 2008, further strengthened by the outbreak in the summer of 2011. However, Salmonella cases in humans have continued to fall, marking a decrease for the seventh consecutive year.

A report from the Danish Centre for Food and Agriculture at Aarhus University says that the production of the food we eat has an impact on the environment but the food we do not eat also has significant adverse effects.

Jackie Linden

Jackie Linden

Top image via Shutterstock

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