Confirmed H5N1 in West Bengal Raises Surveillance Concerns
Recombinomics Commentary 17:05
January 4, 2009
The above comments provide more detail on the culling in the two West Bengal districts, Jalpaiguri and Darjeeling. As noted these areas on the outskirts of Siliguri are surrounded by national parks and wildlife sanctuaries (see zoomed map), strongly suggesting the involvement of wild birds in the spread.
However, the latest outbreaks are only 20-30 miles from international borders with Nepal, China, Bhutan, and Bangladesh, as well as Indian states of Bihar and Sikkim, suggesting H5N1 is in these locations also. However, only Bangladesh has reported recent H5N1 outbreaks, raising serious questions about surveillance in these adjacent regions (see expanded map).
The results this season are similar to last season. That outbreak was confirmed in mid-January and confirmed cases were limited to West Bengal and Bangladesh. There were no confirmed cases in adjacent regions (other than confirmation by China in Tibet). India did culling in adjacent regions, including Assam and Meghalaya, but there was no H5N1 confirmation last season, and only Assam has confirmed H5N1 this season.
The absence of reported H5N1 in these areas reflects poor surveillance or insensitive testing. Routine surveillance uses tests for antibodies, which are insensitive, and tests of cloacal swabs or fecal samples in areas frequented by wild birds, which are also less sensitive than nasphayngeal swabs or tissue extracts. India has yet to report a positive in a migratory bird and reported H5N1 in crows for the first time a few weeks ago, even though dead wild birds associated with dead poultry was widely reported last season in India (and confirmed in wild birds in adjacent regions in Bangladesh).
The H5N1 outbreaks in India and Bangladesh this season are likely to challenge the record levels reported last season, yet surveillance programs in adjacent areas reamain highly suspect.
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