The Food and Drug Administration is trying to find out if the cow ate contaminated feed - a difficult task because the animal may have gotten the disease from feed it ate years before it appeared sick. The disease has an incubation period of four or five years.
Dr. Stephen Sundlof, head of the FDA's Center for Veterinary Medicine, said that an animal could get sick if it eats a little bit of infected material, as little as half a gram.
"Even if a small amount amount of brain or central nervous system (material) were to get into cattle feed, there is the potential for even that very small dose to result in the disease," Sundlof said.
Sundlof said officials are less certain about how much would infect a human. "It's not known what dose would infect humans, but it would higher for humans than for cattle," he said.
Investigators have considered other ways the disease could spread. Although scientists have never found a case of mad cow infection being passed from a mother cow to its calf, they want to test the sick cow's calves for the disease as a precaution.
My questions: How can Sundlof possibly know this (i.e. "... half a gram")? What is the basis for his statement?
For the TSE that affects sheep and goats (scrapie), studies were conducted which used brain tissue (going on memory, will look up when I get home) from a sheep infected with scrapie being surgically implanted into a healthy sheep's brain, with the recipient sheep at some point testing positive and eventually demonstrating clinical signs for scrapie. I believe the amount of the brain tissue used was very small in weight/size.