The prevalence of Culicoides spp. in 3 geographic areas of South Africa.

This research examines the presence and seasonal abundance of Culicoides midges, insects which transmit diseases like Bluetongue and African horse sickness, across three geographical areas in South Africa. The study found that these insects can transmit diseases throughout Winter, and an outbreak can occur once their populations reach a critical level.

Research Context and Methodology

• The main focus of this research was to determine the seasonal fluctuation and abundance of Culicoides midges in three areas of South Africa – Onderstepoort, Mnisi, and Namaqualand. Culicoides midges are vectors, or carriers, for viruses such as Bluetongue virus (BTV) and African horse sickness virus (AHSV).
• The approach involved collecting samples of Culicoides midges from these areas and identifying the species present in each sample. The presence of AHSV and BTV RNA in the midges was also tested using real time reverse transcription quantitative polymerase chain reaction, a technique used to amplify and quantify targeted DNA molecules.

Key Findings

• In the Onderstepoort area, researchers collected over 500,000 Culicoides midges from 27 different species. Throughout the winter, 18 of these species were found, and AHSV and BTV were found in these midges.
• In the Mnisi area, 25 Culicoides species were detected. The BTV RNA was detected in 75.9% of the midge pools collected during winter and 51.2% of those collected during autumn. Moreover, BTV antibodies were found in 95% of cattle in the area, using a competitive enzyme-linked immunosorbent assay (cELISA) for detection, suggesting a high exposure to the virus.
• Eight Culicoides species were found in Namaqualand. Culicoides imicola and Culicoides bolitinos were found to constitute a small portion of the total catches, and AHSV antibodies were detected in 4.4% of 874 equines tested using an indirect ELISA.
• The dominant species in the Onderstepoort and Mnisi areas was Culicoides imicola.
• The findings revealed that the transmission of AHSV and BTV can persist throughout the winter and that an outbreak of these diseases can start as soon as Culicoides populations reach a certain critical level.

Implications of the Study

• This study provides important insights into the abundance and presence of Culicoides spp. in South Africa, and how these insects contribute to the transmission of the Bluetongue and African horse sickness viruses.
• Understanding the seasonal patterns of these insects and their role in disease transmission can help in implementing effective disease control strategies, including targeted insect control measures.
• The finding that the disease can spread even in winter underlines the need for year-round vigilance and disease control measures.