 Antibody (Ig) ELISAs are used to detect historical BVDV infection; these tests have been validated in serum, milk and bulk milk samples.Ig ELISAs do not diagnose active infection but detect the presence of antibodies produced by the animal in response to viral infection.Vaccination also induces an antibody response, which can result in false positive results, therefore it is important to know the vaccination status of the herd or individual when interpreting results.