Abstract
Bluetongue (BT) disease, caused by the non-enveloped bluetongue virus (BTV) belonging to the Reoviridae family, is an economically important disease that affects a wide range of wild and domestic ruminants. Currently, 26 different serotypes of BTV are recognized in the world, of which BTV-8 has been found to exhibit one of the most virulent manifestations of BT disease in livestock. In recent years incursions of BTV-8 in Europe have resulted in significant morbidity and mortality not only in sheep but also in cattle. The molecular and genetic basis of BTV-8 pathogenesis is not known. To understand the genetic basis of BTV-8 pathogenicity, we generated reassortant viruses by replacing the 3 most variable genes, S2, S6 and S10 of a recent isolate of BTV-8, in different combinations into the backbone of an attenuated strain of BTV-1. The growth profiles of these reassortant viruses were then analyzed in two different ovine cell lines derived from different organs, kidney and thymus. Distinct patterns for each reassortant virus in these two cell lines were observed. To determine the pathogenicity of these reassortant viruses, groups of BTV-susceptible sheep were infected with each of these viruses. The data suggested that the clinical manifestations of these two different serotypes, BTV-1 and BTV-8, were slightly distinct and BTV-1, when comprising all 3 genome segments of BTV-8, behaved differently to BTV-1. Our results also suggested that the molecular basis of BT disease is highly complex.
Highlights
IntroductionCurrent address: Foreign Animal Disease Research Unit, USDA/ARS Plum Island Animal Disease Center, NY, USA
Current address: Foreign Animal Disease Research Unit, USDA/ARS Plum Island Animal Disease Center, NY, USA.Bluetongue (BT), an insect-transmitted, non-contagious viral disease of domestic and wild ruminants is caused by bluetongue virus (BTV)
Serum samples were tested against parental BTV-1 and BTV-8 viruses and the neutralization titer was determined as the highest dilution able to neutralize 100 tissue culture infective dose 50 (TCID50) of virus in 50% of replicate wells
Summary
Current address: Foreign Animal Disease Research Unit, USDA/ARS Plum Island Animal Disease Center, NY, USA. The same serotype re-emerged in 2007 and 2008, causing devastating disease in sheep and in cattle with high morbidity and mortality (Elbers et al, 2008a, 2008b; Wilson and Mellor, 2009). Studies involving molecular epidemiology have shown that the most severe disease in northern European sheep and cattle was caused by BTV-8 (Dal Pozzo et al, 2013; Martinelle et al, 2013; Purse et al, 2005). The phenotypic characteristics of the disease caused by these reassortant viruses were analyzed by infection of sheep. Our results suggested that all three proteins together are involved in the disease outcome and that the molecular basis of BTV pathogenicity is highly complex
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