Metchosin -

The critical thing is that it's one or two particular virus strains that have been found capable of infecting humans, and that are sometimes deadly when they do. (See Peace's post at 17 Jun 06 - 08:21 PM.)

The presence of viruses, and even of flu viruses, in birds has been well established; but the records don't indicate whether the particular varieties of recent concern were always common, or have increased their presence recently.

In most cases with older surveys the methods were not available to make detailed determination of subtypes of the viruses found. In the latest case the virus found is probably an H5(?) but the N-type hasn't been determined yet.

Surveillance of migrating bird populations hasn't found very many affected with the H5 and H7 varieties of concern, which some take to mean that those particular kinds have not been widespread. This may (or may not) mean that the migratory birds have some immunity, and don't get infected easily(?)

Or it could mean they haven't been exposed, have little immunity, and it could spread rapidly within wild flocks once picked up in one of them. The assumption has been that the infection can spread rapidly within domestic flocks, and "whole flock extermination" has been used. Large numbers of birds killed doesn't necessarily mean large numbers infected, so the published reports of huge numbers of dead birds don't really tell one very much.

John