The latest information from WHO (on 29 April) gives a total of 126 confirmed human cases of avian influenza A(H7N9) virus, of whom, 24 have died. Since the first reported case in February, all the cases were in China's neighbouring, easternmost provinces of Jiansu, Anhui, Shanghai and Zhejiang. On 25 April, however, came the first report of a case outside China; one person in Taiwan has been confirmed with the virus in Taipei. He had recently returned from the affected area of China.

This viral strain is a triple reassortant H7N9 influenza virus, with components from H7Nx, H11N9 and H9N2 - all of avian origin but at least one element originates in wild birds.

So far, it has not been possible to establish how the virus is transmitted, nor the likelihood of person-to-person transmission.

A joint international mission has recently completed a study of the situation in China at the invitation of the Chinese government.

The mission team reported: "According to available evidence, birds infected by the virus, especially poultry, and the environment contaminated by the virus are the most likely sources of infection. The risk of infection appears most concentrated in live poultry markets".

They said: "Steps taken so far, such as the suspension of live bird markets in Shanghai, were timely and sound. In Shanghai, it appears that so far poultry infections are limited to live markets". However, they cautioned that experts still have only a limited understanding of the full extent of the disease.

The first of the mission's seven recommendations is "to undertake intense and focused investigations to determine the source(s) of human H7N9 infections with a view to taking urgent action to prevent continuing virus spread and its potentially severe consequences for human and animal health".

While they are both influenza viruses that originate in birds and affect humans, there are two differences between this latest H7N9 subtype and H5N1, the one that has spread across much of the globe over the last decade. Firstly, H7N9 has so far affected mainly men and the over 50s, in contrast to the H5N1 type, which infected children and women.

The second difference is that H7N9 is a low-pathogenic form of the virus in poultry and symptoms can easily be missed. The H5N1 type, in contrast, causes very high losses in affected flocks, particularly in chickens and turkeys. It might not have such immediate adverse impacts on the birds as H5N1 but make no mistake, its impacts will surely be felt by the poultry industry.

As we have noted, live birds markets in Shanghai have been closed down and the virus has been found at other similar markets in affected provinces. Furthermore, despite well-founded assurances that there is no risk from properly cooked poultry products, there are signs that sales of poultry meat and eggs are falling in China as a result of market closures and the population's fears of infection.

And there may be consequences for the whole food chain. Already there is speculation in the global trade markets about the possible impacts on maize and soybean demand this year, with China being such a large importer of these feed ingredients.