Differences in experimental virulence of bovine viral diarrhoea viral strains isolated from haemorrhagic syndromes

In the late 1980s, a new hypervirulent and epidemic form of bovine viral di arrhoea virus (BVDV) infection appeared in North America. A similar but spo radic syndrome was later reported in Europe. To compare the pathogenic char acters of the North American and European hypervirulent strains, we inocula ted BVDV naive calves with BVDV strains isolated from haemorrhagic syndrome s originating in Belgium, France and the USA. The experimental procedure co mprised daily clinical examination and measurement of blood and virological parameters. The American BVD890/256 strain induced severe thrombocytopaeni a, profuse diarrhoea and pneumonia in all calves, indicating that hyperviru lent BVDV could be the primary infectious agent of pneumonia. Interestingly , a strong correlation was observed between the intense viraemia and a decr eased platelet count. None of the European strains tested induced significa nt pathological signs, although isolated from cases presenting haemorrhagic syndrome. (C) 2000 Harcourt Publishers Ltd.