Diseases caused by viruses are a constant and major problem for livestock production world wide. The diseases range from highly contagious acute forms with high mortality, to chronic disabling diseases with an insidious effect on production. Such diseases cannot be regarded as static in nature due to the highly mutable nature of viruses and their direct selection at the host level and indirect selection in vectors, inducing changes in pathogenicity. Considerable efforts are needed to control these diseases including accurate and rapid diagnosis using both classical and emerging technologies. The methods used are based on both serological and molecular biological based methods. The ELISA and use of monoclonal antibodies are significant in the serological field whereas the Polymerase Chain reaction (PCR) and its direct and indirect uses for identifying (sequencing) and amplification of gene products, is vital to both research and applied fields. Both areas have to be used in a complementary way in the diagnosis of virus diseases.