TYPING OF BLUETONGUE VIRUS ISOLATES BY SEROLOGICAL AND GENETIC METHODS
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Date
2010-07
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SRI VENKATESWARA VETERINARY UNIVERSITY TIRUPATI - 517 502. (A.P.) INDIA
Abstract
ABSTRACT:
Bluetongue is an arthropod-borne viral disease of cattle, sheep and other ruminants which causes huge economic loses. The BTV belongs to Reoviridae family under the genus Orbivirus is transmitted by the vector Culicoides species. This disease was placed in List 'A' diseases by Office International des Epizooties (OIE). The BTV genome consists of ds RNA with 10 segments that code for 7 structural proteins and 3 non-structural proteins. Among all these L2 segment codes for VP2 proteins which is one of the major outer capsid proteins that elicits virus neutralizing antibodies in infected animals. In addition, this determines the serotype specificity. Targeting this gene and its protein function, various typing techniques were standardized for identifying the BTV isolates up to the serotype level and for molecular characterization studies. The present study deals with the standardization of the serological and genotyping methods for typing of the BTV isolates. The hyper immune sera raised in sheep and used in serum neutralization test which specifically typed the Tirupati, MBN, N15, KMN07 and BTV-16 isolates as BTV-2, 9, 10, 21 and 16 serotypes respectively. In addition, in cross neutralization studies the SNT is able to determines the serological relationship between the serotypes 1 & 2 and between 16 & 21 serotypes. The genotyping was standardized using the RT-PCR assays. With the type specific primers the isolates Tirupati, K8, K3 and KMN07 isolates are typed as BTV-2, 9, 10 and 21 respectively. The N15 isolate which is previously typed as BTV-15, was retyped by this assay as BTV-10. On analyzing the sequence of N15 isolate VP2 gene, it showed 98% homology with that of BTV-10 USA serotype. But the homology is only 89% with that of BTV-10 South Africa reference strain. This signifies the origin of BTV-9 from USA. Both the techniques significantly typed various isolates of BTV to serotype level. In addition these techniques succeeded in identifying the serological relationships and highlighting the importance of topology of BTV serotypes in genotyping.
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