Abstract
Bluetongue disease is caused by bluetongue virus (BTV) and BTV serotype 8 (BTV8) caused great economic damage in Europe during the last decade. From 1998 to 2007, in addition to BTV8, Europe had to face the emergence of BTV1, 2, 4, 9, and 16, spreading in countries where the virus has never been detected before. These unprecedented outbreaks trigger the need to evaluate and compare the clinical, virological and serological features of the European BTV serotypes in the local epidemiological context. In this study groups of calves were infected with one of the following European BTV serotypes, namely BTV1, 2, 4, 9 and 16. For each tested serotype, two groups of three male Holstein calves were used: one group vaccinated against BTV8, the other non-vaccinated. Clinical signs were quantified, viral RNA was detected in blood and organs and serological relationship was assessed. Calves were euthanized 35 days post-infection and necropsied. Most of the infected animals showed mild clinical signs. A partial serological cross reactivity has been reported between BTV8 and BTV4, and between BTV1 and BTV8. BTV2 and BTV4 viral RNA only reached low levels in blood, when compared to other serotypes, whereas in vitro growth assays could not highlight significant differences. Altogether the results of this study support the hypothesis of higher adaptation of some BTV strains to specific hosts, in this case calves. Furthermore, cross-protection resulting from a prior vaccination with BTV8 was highlighted based on cross-neutralization. However, the development of neutralizing antibodies is probably not totally explaining the mild protection induced by the heterologous vaccination.
Highlights
Bluetongue virus (BTV) represents the type species of the Orbivirus genus, family Reoviridae and causes bluetongue disease (BT) in susceptible species [1, 2]
2006, Europe had to face an unprecedented emergence of BTV serotypes 1, 2, 4, 9 and 16 (BTV1, 2, 4, 9, 16) throughout the Mediterranean Basin, including several countries where the virus was never detected before
BTV serotype 8 (BTV8) emergence was spread through Culicoides species that were not known as the historic BTV transmission species, i.e. Culicoides obsoletus complex species [5]
Summary
Bluetongue virus (BTV) represents the type species of the Orbivirus genus, family Reoviridae and causes bluetongue disease (BT) in susceptible species [1, 2]. 2006, Europe had to face an unprecedented emergence of BTV serotypes 1, 2, 4, 9 and 16 (BTV1, 2, 4, 9, 16) throughout the Mediterranean Basin, including several countries where the virus was never detected before. BTV8 emergence was spread through Culicoides species that were not known as the historic BTV transmission species, i.e. Culicoides obsoletus complex species [5]. This epidemic—affecting abundantly cattle whereas previous outbreaks largely occurred in small ruminants—is considered to have caused greater economic damage than any previous
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