The World Health Organisation (WHO) on Wednesday warned that avian influenza remains a threat to humans amid reports that 21 cases have been confirmed worldwide this year, seven of which have been fatal. Dr Takeshi Kasai, regional adviser for communicable disease surveillance and response, said the H5N1 virus could combine with other flu viruses and create a new strain. Health officials in Takeo province reported in February that bird flu had killed thousands of ducks, though no human cases were reported.