Re: Study: Migratory birds not to blame for spread of avian flu
how do you explain the sudden appearance at many different
distant places all through central and south-eastern
Europe within only a few weeks
and almost complete silence -with only few exceptions-
dring other times of the year ?
the travel paths in early Febr. : Romania-Greece-Italy
Romania-Croatia-Austria-Bavaria-(France?) could well be observed.
Here is a quick summary. The test for detecting Qinghai H5N1 usually produces false negatives because it is so insensitive. If the right sample is collected at the right time, the sample is positive. However, there are dozens of factors that can create lower levels.
Vitually all Qinghai isolates have PB2 E627K. This reduces the level of H5N1 because it slows down replication at a bird's body temperature. Other influenza and other H5N1's have 627E, so the influenza levels are higher at the bird's body temperature, because activity is highest at 41 C.
As a result, low path is detected in live birds, but H5N1 Qinghai is VERY rare. To detect H5N1, most hosts have to be dead or near death. On farms, where there are many dead and dying birds, getting a positive is fairly easy, especially if the right birds are chosen and multiple birds are tested.
In the field, the story is very different.
Most of the testing is of live healthy birds and H5N1 levels are low. Dead birds decompose, so if collected shortly after death, positives can be obtained. In the cold, the virus is also more stable, so it is easier to transmit in the cold. Some species, like mute swans, may have higher levels, or they may be more noticable when they are dead or dying because they are large.
In any event, the testing is rather poor, and some testing has additional problems, like DEFRA allowing swabs to dry out prior to testing. That is why they get almost no isolates - they can't even get low path.
The bottom line is that getting a Qinghai positive in a live wild bird is not easy. In the US, the vast majority of testing was in healthy live birds. All were negative. When H5 was found in dead ducks on PEI, the level of RNA was low, and the sample was held until it degraded and Winnipeg failed to reproduce the positive.
Getting false negatives is a trivial task. as has been demonstrated in North America, Europe, the Middle East, and Africa,