d) They represent the main reservoir for BVDV in the herd and; therefore, must be identified The only way to do this is to assay for either infectious virus (cell culture or IPX) or by antigen capture (ELISA).

e) Only PI animals will succumb to fatal mucosal disease. There is no known treatment to reverse the persistent infection. Vaccination will not prevent PI animals from contracting mucosal disease (However, vaccination of dams before pregnancy should prevent their foetuses becoming PI).