MOLECULAR EPIDEMIOLOGY OF AFRICAN HORSE SICKNESS VIRUS-BASED ON ANALYSES AND COMPARISONS OF GENOME SEGMENT-7 AND SEGMENT-10

This paper describes a method to rapidly identify African horse sickne ss virus (AHSV), using a single tube reverse transcription polymerase chain reaction (PCR). This method was used to amplify cDNA copies of g enome segments 7 and 10 from several different AHSV strains, of differ ent serotypes, which were then analysed by sequencing and/or endonucle ase digestion. AHSV VP7 (encoded by genome segment 7) is one of the tw o major capsid proteins of the inner capsid layer, forming the outer s urface of the core particle. VP7 is highly conserved and is the major serogroup specific antigen common to all nine AHSV serotypes. Digestio n of the 1179 bp cDNA with restriction enzymes, allowed differentiatio n of several strains of different serotypes and identified six distinc t groups containing AHSV-1, 3, 6 and 8; AHSV-2; AHSV-4; AHSV-5; AHSV-7 ; and AHSV-9. Differences were detected between wild type viruses and vaccine strains that had been attenuated by multiple passage in suckli ng mouse brain or in tissue cultures. RFLP analysis was also used to s tudy variation the 758 bp cDNA copies of AHSV genome segment 10, which encodes the two small non-structural membrane proteins NS3 and NS3a. In this way it was possible to distinguish each of the strains tested, except AHSV 4 (USDA) and AHSV 9 (USDA). However, these isolates could be distinguished by RFLP analysis of genome segment 7 cDNA. Using seq uence analysis of genome segment 10 we were able to classify the virus isolates into three groups: AHSV-1, 2 and 8; AHSV-3 and 7; AHSV 4, 5, 6 and 9. These studies confirmed that the virus which first appeared in central Spain in July 1987, subsequently spread into northern Moroc co in October 1989.