Bird Flu/Mad Cow diseases

Ok from what I understand this bird flu disease can be quite quick. What I am wondering is about the Mad Cow disease. According to what I have read, this may not manifest for years after having contracted it. It can lay quiet inside a body for years before anyone knows they have it.
If this is true, than thousands or millions could have this disease and not know it. If they only have tested so many cows, every so long, then how does one know if they are infected?

You are about 10 years too late with this post mate.

Mad cow disease, or or the human form CJD has claimed just over 150 human lives, only 1 human case outside of the uk.

www.cjd.ed.ac.uk...

as you can see from the table cjd is on the decline and no proff has ever been established between eating infected meat and catching cjd.

really nothing to worry about mate.

other forms of bse are naturaly occuring and mainly affect the elderly.