Survivors become carriers and continue to spread the virus, which persists in all body fluids including milk, dead skin, semen and embryos. There are more than 1,200 confirmed cases in Britain and 1.5 million animals have either been slaughtered or are scheduled to be killed. The disease starts as blisters full of virus particles. The particles become airborne when the blister ruptures and quickly spreads. They can produce billions and billions of virus so when these blisters rupture they get dispersed throughout the air.
Sheep also harbor the virus for two weeks without exhibiting outward symptoms.
Britain's problem is exacerbated by the size of some flocks. With more than 1,000 sheep in a flock, it is nearly impossible to check each animal every day. It is believed the disease started on a swill-feeding operation where hogs were fed food scraps from a local restaurant that included illegally imported meat from Asia. The virus is similar to the influenza bug that strikes people. It is constantly changing so many vaccines are not effective against all strains.