Clinical appearance and pathology of cattle persistently infected with bovine viral diarrhoea virus of different genetic subgroups.

Bovine viral diarrhoea (BVD) is an economically important cattle disease with a world-wide distribution that is caused by BVD virus, a pestivirus of the flaviviridae family. BVD viruses are genetically highly variable. They are classified into two genetic species (BVDV-1 and -2) that are further divided into numerous subgroups, particularly for BVDV-1. The complexity of these viruses is also reflected in their interaction with the host animals. Infections are either transient or persistent and can cause a wide spectrum of clinical signs, from no or very mild disease to severe forms, reminiscent of viral haemorrhagic fevers. In this work, we have analysed the clinical signs and the pathology of BVD viral infections in a cattle population where different subgroups of BVDV-1 genotype viruses are endemic. In addition, we have examined potential virulence properties of BVDV-1 subgroups during persistent infection by comparing the viral subgroups present in clinical cases with those detected in persistently infected (PI) animals sampled for epidemiological criteria, irrespective of their health condition. Furthermore, the clinical and postmortem findings were compared with respect to genetic characteristics of the viruses isolated from these animals. Our results indicate that the BVDV positive animals fall roughly into two categories, depending on the primary organ affected and the age, with lung-centred pathology occurring mainly in young animals and mucosal pathology predominantly in older animals. Furthermore, we found a markedly higher proportion of representatives of the BVDV-1e subgroup in stillborn calves and aborted foetuses originating from epidemically unrelated cattle herds, suggesting that BVDV-1e may play a special role in prenatal and perinatal losses.