Persistently infected calves are loaded with virus. A test on serum from the calf has been used to detect the presence of the virus. Virus is also present in the skin and is particularly associated with hair follicles. A new test that uses immunohistochemistry can be performed on formalin-fixed sections of skin, such as an ear notch sample. Antibodies to the virus are used to attach to viral particles.
Markers then attach to the complex to visualize the location of viral presence.
Tests are under way to determine differences in sensitivity or specificity between the serum and skin tests. At this point, either test can be used to determine the presence of persistently infected BVD calves.