Library Dissertation Showcase

Assessing the prevalence of African horse sickness in Culicoides across Africa

  • Year of Publication:
  • 2021

African Horse Sickness Virus (AHSV) is thought to be the most lethal arboviral disease of Equidae. The disease is endemic in tropical sub-Saharan Africa and without mitigation AHSV can exhibit mortality rates of up to 90% in horses. Transmission between hosts is facilitated by biting midges of the genus Culicoides (Diptera: Ceratopogonidae). This review examines the prevalence of AHSV in Culicoides collected in a variety of locations across Namibia and South Africa by compiling consistent quantitative data from published sources. Analysis was completed using R-studio in line with the research aims by; mapping Culicoides abundances across sampling sites, comparing the relationship between C.imicola and AHSV prevalence and assessing if AHSV prevalence is changing over time. The number of Culicoides species at each site was variable ranging from 2-67 species at each site. The majority of Culicoides collections saw C. imicola in the highest abundance compared to other species, barring Clarens Valley in South Africa where C.bolitinos (another vector of AHSV) was recorded in highest abundance and some Namibian sites. This study established the presence of C.imicola a key determinant for high AHSV prevalence in Culicoides, although some regions with a high abundance of C. imicola had low AHSV prevalence, likely due to the lack of AHSV in hosts in the area for them to bite and become infected. The sparsity of studies determining prevalence of AHSV in Culicoides along with the variability in experimental designs in studies included in this review highlights the need for standardised protocol when sampling to significantly assess the changing AHSV prevalence. Alarmingly C.imicola is already present on all continents except Antarctica and climate change is amplifying their abundance and global distribution. Additionally, C.imicola are also vectoring another morphologically similar virus to AHSV, known as Blue-tongue virus which has caused unprecedented outbreaks from 2006 across Europe.

 Keywords: Arbovirus, African Horse sickness, Culicoides, Climate change, Vector, Equidae, Culicoides imicola.

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