a) They are persistently infected with BVDVnc and never BVDVc.
b) They rarely make antibody to the persisting virus. Therefore, they are often antibody negative to BVDV: However, they can make antibody to other BVDV isolates that are 'heterologous'to the persisting virus. As a result, they can have low level of BVDV antibodies to 'heterologous' virus.

c) The clinical appearance of P.I. animals can range from:severe congenital damage ( eg ataxia) to unthrifty and increased susceptibility to respiratory/enteric diseases to clinically normal.