Variation in the NS3 gene and protein in South African isolates of bluetongue and equine encephalosis viruses

Faculty of Veterinary Science, University of Pretoria, Πρετόρια/Πόλη του Ακρωτηρίου, Gauteng, South Africa
Journal of General Virology (Impact Factor: 3.18). 04/2003; 84(Pt 3):581-90. DOI: 10.1099/vir.0.18749-0
Source: PubMed


Bluetongue virus (BTV) and equine encephalosis virus (EEV) are agriculturally important orbiviruses transmitted by biting midges of the genus Culicoides. The smallest viral genome segment, S10, encodes two small nonstructural proteins, NS3 and NS3A, which mediate the release of virus particles from infected cells and may subsequently influence the natural dispersion of these viruses. The NS3 gene and protein sequences of South African isolates of these viruses were determined, analysed and compared with cognate orbivirus genes from around the world. The South African BTV NS3 genes were found to have the highest level of sequence variation for BTV (20 %), while the highest level of protein variation of BTV NS3 (10 %) was found between South African and Asian BTV isolates. The inferred NS3 gene phylogeny of the South African BTV isolates grouped them with BTV isolates from the United States, while the Asian BTV isolates grouped into a separate lineage. The level of variation found in the NS3 gene and protein of EEV was higher than that found for BTV and reached 25 and 17 % on the nucleotide and amino acid levels, respectively. The EEV isolates formed a lineage independent from that of the other orbiviruses. This lineage segregated further into two clusters that corresponded to the northern and southern regions of South Africa. The geographical distribution of these isolates may be related to the distribution of the Culicoides subspecies that transmit them.

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Available from: Christiaan Potgieter, Jan 07, 2014
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    • "However, the analysis of these samples also indicated the presence of serotype 17, which had up till then not been detected in the country [62]. A single molecular epidemiological study using the NS3/A gene of BTV has been conducted in South Africa [63]. In this study different serotypes that were collected from widespread regions throughout the country were analyzed. "
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    ABSTRACT: Bluetongue (BT) is a non-contagious, infectious, arthropod transmitted viral disease of domestic and wild ruminants that is caused by the bluetongue virus (BTV), the prototype member of the Orbivirus genus in the family Reoviridae. Bluetongue was first described in South Africa, where it has probably been endemic in wild ruminants since antiquity. Since its discovery BT has had a major impact on sheep breeders in the country and has therefore been a key focus of research at the Onderstepoort Veterinary Research Institute in Pretoria. Several key discoveries were made at this Institute, including the demonstration that the aetiological agent of BT was a dsRNA virus that is transmitted by Culicoides midges and that multiple BTV serotypes circulate in nature. It is currently recognized that BT is endemic throughout most of South Africa and 22 of the 26 known serotypes have been detected in the region. Multiple serotypes circulate each vector season with the occurrence of different serotypes depending largely on herd -immunity. Indigenous sheep breeds, cattle and wild ruminants are frequently infected but rarely demonstrate clinical signs, whereas improved European sheep breeds are most susceptible. The immunization of susceptible sheep remains the most effective and practical control measure against BT. In order to protect sheep against multiple circulating serotypes, three pentavalent attenuated vaccines have been developed. Despite the proven efficacy of these vaccines in protecting sheep against the disease, several disadvantages are associated with their use in the field.
    Virology Journal 09/2012; 9(1):198. DOI:10.1186/1743-422X-9-198 · 2.18 Impact Factor
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    • "The inferred amino acid sequences of the S10 genes were aligned using default parameters of CLUSTAL X (Thompson et al., 1997), and the corresponding nt sequences were aligned based on the amino acid alignment. The S10 gene of epizootic hemorrhagic disease virus serotype 1 was used as the out-group to root the trees (Jensen and Wilson, 1995); previous analyses demonstrated that the S10 genes of BTV form a monophyletic group (Pierce et al., 1998; van Niekerk et al., 2003). Phylogenetic trees were inferred from nt data using unweighted maximum parsimony (MP). "
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    ABSTRACT: Comparison of the deduced amino acid sequences of the genes (S10) encoding the NS3 protein of 137 strains of bluetongue virus (BTV) from Africa, the Americas, Asia, Australia and the Mediterranean Basin showed limited variation. Common to all NS3 sequences were potential glycosylation sites at amino acid residues 63 and 150 and a cysteine at residue 137, whereas a cysteine at residue 181 was not conserved. The PPXY and PS/TAP late-domain motifs were conserved in all but three of the viruses. Phylogenetic analyses of these same sequences yielded two principal clades that grouped the viruses irrespective of their serotype or year of isolation (1900-2003). All viruses from Asia and Australia were grouped in one clade, whereas those from the other regions were present in both clades. Each clade segregated into distinct subclades that included viruses from single or multiple regions, and the S10 genes of some field viruses were identical to those of live-attenuated BTV vaccines. There was no evidence of positive selection on the S10 gene as assessed by reconstruction of ancestral codon states on the phylogeny, rather the functional constraints of the NS3 protein are expressed through substantial negative (purifying) selection.
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    • "Seg- 2 and Seg-6, encoding the outer capsid proteins VP2 and VP5) and more conserved genes (e.g. Seg-10, encoding the non-structural proteins, or the structural proteins of the virus core) (deMattos et al., 1996; Pierce et al., 1998; Bonneau et al., 1999; van Niekerk et al., 2003; Mertens, 2004). It has been suggested by some workers that variations in the sequence of Seg-10 could be used for geographical 'topotyping' of viral strains (Balasurya et al., 2003). "
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    ABSTRACT: The sequence of the genome segment 10 (Seg-10) encoding NS3/NS3A was determined for 19 field isolates of Bluetongue virus (BTV) of serotypes BTV-1, BTV-4, BTV-9 and BTV-16, derived from epizootics in Greece in the years 1979 and 1998-2001. The aim of the study was to define the molecular epidemiology of the virus in this part of the Mediterranean basin. On the basis of the Seg-10 sequences, the isolates grouped into two distinct phylogenetic clusters. These were Greek group I of solely serotype BTV-4 viruses, and Greek group II of serotypes BTV-1, BTV-9 and BTV-16 viruses. The isolates in Greek group I clustered with the Corsican and Tunisian BTV-2 serotypes and US group II strains of BTV-10 and BTV-13 serotypes, while those in Greek group II with Chinese, Indian and Australian viruses of different serotypes suggesting that viruses derived from two distinct ecosystems have caused BT incursions in Greece over the last 25 years. The NS3/NS3A sequences of most of the BTV-4 isolates were identical, irrespective of the year of isolation, geographical location and host species or tissue origin. Maximum of 15-16% nucleic acid sequence variation, but only 4% deduced amino acid substitution, were observed between groups I and II. Furthermore, the clustering of the NS3/NS3A sequences was independent of the viral serotype, indicating the occurrence of genome segment reassortment during the course of evolution of the viruses.
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