The Chinese veterinary authority this week reported finding no less than five different subtypes of the highly pathogenic avian influenza virus during September, apparently during a programme of national surveillance on one day. The types were H5N1, H5N3, H5N8, H5N6 and H5N2.

The great majority of the 51 'outbreaks' reported to the World Organisation for Animal Health (OIE) were virus-positive samples taken from birds and the environment at markets. However, at least two poultry flocks were affected; all the birds there were destroyed.

That there were so many positive samples over such a wide geographical area and of so many types is cause for concern. The next pandemic affecting humans or livestock or both is likely to emerge under circumstances just like these. Flu viruses are more active in cool weather and, were one highly pathogenic type to cross with one that is easily transmitted, we could be facing a perfect storm for the development of a pandemic.

In the meantime, cases of H7N9 flu in people continue to rumble on in China. Two cases were reported in August and a further two last month, bringing the total number of cases to 440 in mainland China. According to a case series kept by FluTrackers, the overall total now stands at 456 cases.

A spokesman from Centre for Health Protection in Hong Kong has warned that more sporadic H7N9 infections are expected in affected and possibly neighbouring areas and that heightened vigilance is needed.

At the beginning of October, the World Health Organization reported that 668 laboratory-confirmed human cases of avian influenza A(H5N1) virus infection have been officially reported to date from 16 countries. Of these cases, 393 have died. This virus has caused several cases recently in Egypt.