 A standard test to assess whether virus has been circulating recently is to perform an Ig ELISA on blood from 5–10 young stock that have not been vaccinated, aged between 9 and 18 months.A positive result indicates exposure to BVDV, but also that any positive animals are very unlikely to be PI animals themselves.A positive result in a pregnant female indicates that she has previously been either vaccinated or infected with BVDV and could possibly be carrying a PI fetus, so antigen testing of the newborn is vital to rule this out.