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 __.
The best way to complete the argument is to destroy all cattle in areas where BSE occurs and raise cattle only in areas where BSE is known not to have spread.