Pestivirus diversity
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Pestivirus diversity
A meeting was held at the Forte Crest Hotel, Glasgow on 10th August 1993 to discuss the topic of antigenic diversity in pestiviruses, to consider whether such diversity had any practical significance in terms of control, and the plan steps to correlate and collate the considerable body of data already existing on this subject in various laboratories around the world. The meeting was chaired by Prof. Marian Horzinek, and sponsored by SmithKline Beecham (represented by Dr. N. Zygraich). It was agreed that antigenic diversity exists among the pestivirus genus, and that this could not be readily defined in conventional terms of serotypes. Hog cholera virus strains appear to form a tight antigenic cluster and can be adequately defined for practical purposes by the binding of species-specific monoclonals to the dominant epitope on the gp55. This is important for regulatory authorities seeking to verify their hog cholera-free status in the face of endemic infection with other pestiviruses, which sometimes spread from ruminants into pigs. The group would not address further the definition of HCV. The terms bovine viral diarrhoea virus (BVDV) and border disease virus (BDV) are used rather loosely. They could refer to virtually identical viruses isolated respectively from cattle and sheep, or to widely divergent viruses isolated from a single species. The definition of virus species on the basis of host broke down further when non-HCV pestiviruses isolated from pigs were labelled BVDV or BDV. No satisfactory nomenclature exists for pestiviruses isolated from ruminants other than cattle of sheep. There is good evidence accumulating from a number of research teams that ruminant pestiviruses tend to cluster in 2-3 distinct groups. This is supported by three strands of evidence - polyclonal neutralisation tests, murine monoclonal binding studies, and genetic sequence data. The fact that the three approaches give broadly similar results confounds to some extent the suggestion that murine antibodies may not detect meaningful epitopes in terms of immunity in ruminants. It is hoped that an ad hoc group of pestivirus workers can make progress by sharing data and exchanging reagents with the aim of reaching a consensus view. In particular there is no certainty that pestivirus strains circulating in one country of continent are the same as those elsewhere, although it is commonly assumed that they are so. The question of antigenic diversity is important practically, most particularly as it raises the spectre of naturally occurring vaccine escape variants. There is evidence from USA that such variants do arise in vaccinated cattle. Nevertheless a view is widely held that single strain vaccines provide reasonable protection in most cases. Pestiviruses present a challenge for the vaccinologist because of the need to prevent fetal infection in pregnant dams exposed to infection. Only by protecting the fetus can the establishment of persistently-infected offspring be prevented and the main cycle of infection broke
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