But WHO says virus' spread from daughter to mother is one-off Thai health officials said yesterday that a woman who died of bird flu had probably caught it from her daughter, but that they remained convinced it was an isolated case of human-to-human transmission. The WHO's top infectious diseases expert, Klaus Stohr, stressed that human-to-human transmission of the bird flu known as H5N1 was not new and that the case did not point to an imminent pandemic. Suspicions of human-to-human spread of bird flu were raised on Monday when the 11-year-old girl's aunt was also confirmed as having the disease, which is usually transmitted by contact with infected poultry. She is recovering in a hospital near Bangkok. Samples were taken from the two women, although the girl had been cremated before health officials became concerned. Results of World Health Organisation tests to determine if the women died because H5N1 had mutated into a deadly new strain by mixing with human influenza should be known by the end of the week. Dr Stohr said that human-to-human transmission of bird flu was expected and had occurred in Hong Kong in 1997 and last year in the Netherlands. 'It is not surprising that this virus, in a very limited, unsustained way, is transmitted in very short chains of infection,' he said from Geneva. 'But these cases must be investigated thoroughly to make sure that we would immediately detect any sustained human-to-human transmission.' Such a scenario worried infectious diseases experts, Dr Stohr said, because while there were vaccines for normal H3 human influenza, none had yet been developed for H5N1. 'The sustained, human-to-human transmission, where a continuous spread from one person to another occurs, could mark the beginning of a pandemic,' he warned. At least 29 people have died of bird flu in Southeast Asia this year - 19 in Vietnam and 10 in Thailand. Six countries have been affected and more than 100 million poultry slaughtered to stop the spread of the disease. In the case confirmed yesterday, the 26-year-old woman from northwestern Kamphaeng Phet had cared for her daughter in hospital. The girl died of bird flu-like symptoms on September 12 and her mother seven days later. A Thai Health Ministry statement issued yesterday said: 'Although the finding of probable human-to-human transmission is clearly of concern, there is currently no evidence of ongoing chains of transmission or risk to persons outside of the affected province.' Researchers said earlier this week that Asian governments were not doing enough to stop the spread of H5N1. They said poultry were being reintroduced to areas that had been infected too quickly and that surveillance was not being carried out properly.