CLINICAL-VIROLOGICAL COURSE AFTER SUPERIN FECTION OF PERSISTENTLY INFECTED CATTLE WITH STRAINS OF CYTOPATHOGENIC BOVINE VIRAL DIARRHEA VIRUS

Vaccination with live cytopathogenic (cp) bovine viral diarrhoea virus (BVDV) is often used for control of this disease. In animals which ar e persistently infected with noncytopathogenic (ncp) BVDV this can lea d to the outbreak of mucosal disease (MD). To simulate vaccination of such animals and to monitor the clinical-virological course after supe rinfection, nine clinically healthy carves which were persistently vir emic were superinfected with different cp BVDV strains. One animal suc cumbed to early onset MD within three weeks after superinfection. Duri ng the observation period of 18 months four animals developed severe c linical signs. While two animals developed late onset MD, the other tw o had to be euthanized due to clinical signs which could not be relate d to the superinfecting BVDV. These results indicated that after super infection or vaccination of persistently infected calves with cp BVDV the probability of developing early and / or late onset MD is signific antly increased. The risks arising from uncritical vaccination of herd s with unknown virological status in relation with the control of BVDV conforming to the actual official guidelines are discussed.