[BEIJING] A new study by Chinese scientists suggests a highly possible human-to-human transmission of H5N1 bird flu virus.
Publishing their study this week (8 April) in The Lancet, lead author Wang Yu, director of the Chinese Center for Disease Control and Prevention (China CDC) and colleagues analysed two human cases of bird flu that occurred within the same family in eastern China's Jiangsu Province in December 2007.
The 24-year-old son died of H5N1 infection on 2 December, the fifth day of his hospitalisation. Two days after his death, his 52-year-old father developed typical flu symptoms such as fever, chill and cough. He was diagnosed with H5N1 infection, and survived only after receiving early antiviral treatment.
The researchers investigated the men's exposure to both poultry and people, and found the son's only plausible exposure to H5N1 was a visit to a poultry market six days before the onset of illness.
The father had substantial unprotected exposure to his ill son, and the researchers could find no evidence of him coming into contact with live poultry or being exposed to H5N1 by any other transmission channel.
The H5N1 viruses isolated from father and son were also found to have virtually the same genetic structures.
"We believe that the index case [the son] transmitted H5N1 virus to his father while his father cared for him in the hospital," write the researchers.
But they have found it difficult to explain why the son's mother and girlfriend — both of whom had substantial unprotected exposure to him during his hospitalisation — did not become infected.
"We could not find any apparent difference between the exposure forms of the father and the other two [the mother and girlfriend]," says co-author Shu Yuelong, a senior researcher of China CDC.
"The situation indicates that we are far from understanding the clear pathogenic mechanism of bird flu," he told SciDev.Net.
In an accompanying comment, Jeremy Farrar of the Hospital for Tropical Diseases in Ho Chi Minh City, Vietnam, and colleagues say that all published incidents of possible or probable person-to-person transmission are currently between genetically related individuals.
"Whatever the underlying determinants, if we continue to experience widespread, uncontrolled outbreaks of H5N1 in poultry, the appearance of strains well adapted to human beings might just be matter of time."
The Lancet doi 10.1016/S0140-6736(08)60493-6 (2008)