A surge in human cases of H5N1 bird flu in China, despite few outbreaks of the virus in domestic poultry flocks, has left experts puzzled, The Lancet reports.
Six of this year's eight human cases have occurred in provinces that have been unaffected by poultry outbreaks.
This has led to concerns that the H5N1 virus might have changed substantially, although the nature of that change is unclear.
"Whether that change is in the virus, in how it is spread, in how poultry are responding to it, or in human behaviour to bypass public-health measures and avoid a loss of income when flocks are culled, or is simply … better surveillance and testing, is not yet clear," says the article.
The lack of poultry outbreaks spells trouble because the birds normally serve as a sentinel, sounding the alarm.
Some experts point to the owners of sick and dying birds, who might be omitting to report the disease, and to veterinary authorities, who might be failing to recognise it. There is also speculation over "deliberate suppression of reports due to the severe consequences associated with reporting".
To date, China has identified H5N1 bird flu in 38 people, 25 of whom have died.
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