Outbreak of bovine viral diarrhoe on Dutch dairy farms induced by a BHV1 marker vaccine contaminated with BDVD type 2

On 23 February 1999, the Dutch Animal Health Service advised all Dutch vete rinary practices to postpone vaccination against bovine herpesvirus 1 (BHV1 ) immediately. The day before severe disease problems were diagnosed on fou r dairy farms after vaccination with the same batch of BHV1 marker vaccine. Using monoclonal antibodies, bovine virusdiarrhoea virus (BVDV) type 2 was found in the vaccine batch. This paper describes an outbreak of BVDV type 2 infection caused by the use of a batch of modified live BHV1 marker vacci ne contaminated with BDVD. Sources of information used were reports of farm visits, minutes of meeting s, laboratory results, and oral communications from the people involved. The first symptoms of disease were observed on average six days after vacci nation. Morbidity was high on 11 of the 12 farms. On five farms more than 7 0% of the animals became ill, while on one farm no symptoms could be detect ed. During the first week after vaccination, feed intake and milk productio n decreased. During the second week, some animals became clinically disease d having nasal discharge, fever, and diarrhoea. At the end of the second we ek and at the start of the third week, the number of diseased animals incre ased rapidly, the symptoms became more severe, and some animals died. Morta lity varied among herds. Necropsy most often revealed erosions and ulcers o f the mucosa of the digestive tract. In addition, degeneration of the liver , hyperaemia of the abomasum, and swollen mesenterial lymph nodes and swoll en spleen were found. On 11 of the 12 farms all animals were culled between 32 and 68 days after vaccination after an agreement was reached with the m anufacturer of the vaccine. This was the third outbreak of BVD in cattle after administration of a cont aminated vaccine in the Netherlands. The possibilities to prevent contamina tion of a vaccine as a consequence of infection of fetal calf serum with BV DV are discussed. Improvement of controls to prevent contamination before a nd during vaccine production, and improvement of the monitoring of side-eff ects is necessary.