This work was aimed at addressing issues of misconception that hamper the advancement of bovine viral diarrhea virus (BVDV) control in a Belgian context. To demonstrate that recognizing BVDV infection by its clinical presentations is difficult, the detailed pathology and clinical presentations associated with BVDV infections were documented in three case reports. A subclinical form of BVDV infection was highlighted by looking at differences in bulk milk somatic cell counts between BVDV-infected and non-infected herds. Furthermore, it was assessed whether the BVDV management currently in practice in Belgium is efficient. Finally, some recommendations were made for the Belgian plan to control BVD in the future and eventually to eradicate the BVD virus by bringing together current general knowledge and findings originating from this thesis.
Field experience reveals that not everyone is convinced of the proposition that BVD cannot sufficiently be recognized by its clinical symptoms. The cases described here show that the clinical presentations can be rare and various. In a first case, cytopathic BVDV was detected in a 10-days-old calf during an outbreak of hemorrhagic neonatal diarrhea. Since non-cytopathic BVDV had not been detected in the same animal, this was an extraordinary finding, in particular because of the young age of the calf. Moreover, the case pointed to the role of BVDV in co-infections. In the two other cases, attention was not immediately drawn to BVDV as a potential cause. A 2-day-old calf showed spontaneous skin bleeding and thrombocytopenia. By testing blood samples, it was proved that the calf was persistently infected with a BVDV1b strain. The other case reported was of a cow suffering from hemorrhagic proctocolitis. The cow was transiently infected with BVDV1b. Although it is still generally accepted that BVDV2 is almost exclusively responsible for BVDV associated with severe disease, both the calf and the cow described were infected with BVDV1b.
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