It is not known whether bovine spongiform encephalopathy (BSE), a disease of cattle invariably deadly to them, can be transmitted directly from one infected animal to another at all stages of the infection. If it can be, there is now a reservoir of infected cattle incubating the disease. There are no diagnostic tests to identify infected animals before the animals show overt symptoms. Ttherefore, if such direct transmission occurs, the disease cannot be eradicated by __.
Removing from the herd and destroying any diseased animal as soon as it shows the typical symptoms of advanced BSE best completes the argument.