Mrzzy, we all have to get our food from somewhere. As Llanfair and Greyeyes say, basically it stops the herd being usable for food. Dairy cattle never recover their milk yield, and beef cattle (and other animals raised for meat) don't put on weight properly. And it pretty much sterilises the herd: animals don't breed as much, and those that do, their offspring are sickly.

Now imagine that, uncontrolled. What happens to the world's food supplies when this goes down? A very scarey thought, especially if it reaches areas where they're still on subsistence farming...

AFAIK, no-one's tested to see whether animals eventually get immunity to it by natural means. The trouble is that even if they could, you'd then have to strike out several years of meat production, and no government can afford to support the entire agricultural industry in its country for several years.

Incidentally, NewScientist reported that there's a new drug concept coming around which might provide a new vaccine, but that's not coming out for several years yet.

Grab.