VP2 gene phylogenetic characterization of field isolates of African horsesickness virus serotype 7 circulating in South Africa during the time of the 1999 African horsesickness outbreak in the Western Cape.

This research describes a genetic study that aimed to trace the origins of an outbreak of African horsesickness in South Africa in 1999, by examining the genetic sequences of the virus across different geographical regions in the country.

Introduction and Research Purpose

• The research focuses on the VP2 gene of African horsesickness virus (AHSV) serotype 7, which was responsible for the outbreak in 1998-1999. A total of 16 AHSV 7 isolates were studied, thirteen of which were isolated during the outbreak and three being historical AHSV 7 isolates.
• The main objectives of this work were to establish a database of virus isolates along with their time and location of isolation, and to trace the origin of the outbreak in the Western Cape area of South Africa using the VP2-gene phylogenetic analysis of the virus.

Research Methodology

• Researchers extracted full-length cDNA copies of the VP2 genes of the virus isolates.
• The nucleic acid sequence data of a 786 base pair region was used for genetic characterization and to establish relationships between the virus isolates.

Results and Interpretation

• It was observed that the nucleic acid identities between the isolates ranged between 95.5% and 100%.
• Isolates originating from the same geographical region grouped together, indicating localization of specific virus strains.
• The characterization of the field isolates revealed two distinct AHSV 7 lineages circulating in South Africa during the studied period.
• These lineages or clades were reflective of the geographical divisions, confirming the hypothesis that the virus lineage could be specific to a region.
• The average nucleic acid divergence between these two clades was noted to be 4.3%. The divergence within the clades was found to be 0.5% and 0.1% respectively.
• Basing on these genetic differences, researchers suggested that the 1999 outbreak in the Western Cape may have originated from the Kwazulu Natal Province.

Conclusions and Future Work

• The research successfully employed genetic analysis to trace the origin of an AHS outbreak, indicating its potential as a tool in epidemiological studies and disease control strategies.
• These findings provide a foundation to build a substantial database of the AHSV, which can help to better understand the mechanism of virus transmission and evolution.
• However, additional data on more recent isolates and from other regions would be necessary to validate the observed patterns and to get a more comprehensive understanding of the AHSV’s geographical distribution and temporal variations.