How do they know swine flu originated in Mexico...?

[dinny]

And not previously, somewhere else in the world if they only started testing for it fairly recently...?

WMMC: Yes essentially that is right, except that seasonal influenza is really only a localised disease and doesn't affect the immune system in the way that say measles does. The systemic symptoms and signs of flu are pretty much all due to the pyrogenic effects of the immune response; not the virus spreading through the body.

However, influenza has severe effects on the mucosal lining of the respiratory tract, and affects the basic protection mechanisms such as cilia (the little beating hairs that physically sweep stuff out of the trachea and into the throat). There's a few bacterial pathogens that take advantage of this and can overcome the basic defences and get in to cause more serious diseases (the so-called secondary bacterial infections which may present at the same time).

H5N1 is rather a special case and the evidence shows it can seriously disturb the immune system at a regulatory level. Similar to SARS coronavirus.

At the moment, swine H1N1v is much more like seasonal flu than H5N1 thank goodness!

Musu, wonderful info, thank you (again)

yes, thank you Musu (and wmmc too)

so is swine flu truly mild in most people? really worry about my 4 month old

Truly, dinny, as far as word-of-mouth and people here in SW London that I know who have it/have had it. Not pleasant, for some more than others, but not serious either.