Culicoides in relation to transmission of African horse sickness virus in The Gambia.

The research paper focuses on biting midges (genus Culicoides) in The Gambia and their potential role in the transmission of African horse sickness virus (AHSV) and bluetongue virus (BTV), diseases that impact horses and donkeys.

Research area and Methodology

• The researchers conducted twelve light trap collections of Culicoides near overnight shelters of horses and donkeys across four villages in the Central River Division of The Gambia. The aim was to investigate the variety of Culicoides species present in the area and determine potential vectors of diseases affecting equines, namely AHSV and BTV.
• Formalin-preserved female midges were tested using antigen capture ELISAs for AHSV and BTV, viruses that may be carried and transmitted by these insects. A total of 2286 females in 240 aliquots were examined for the presence of viruses.

Findings

• Out of fourteen species of Culicoides identified in the light trap collections, five were newly recognized in The Gambia. With these findings, the total count of recognized Culicoides species in The Gambia rises to twenty-nine.
• The majority of the insects captured were species known or suspected to be vectors of AHSV and BTV. About 83% of female captures belonged to these species, with 65% being either C. imicola or its sibling species, C. miombo.
• Significantly, the researchers found the number of female Culicoides (potential disease vectors) captured in the late dry season were almost as large as in the early dry season, suggesting that the harsh heat and dryness did not drastically reduce the population.
• Despite comprehensive testing, no viruses were detected amongst the tested female midges.

Implications

• The research indicates a strong presence of Culicoides species that are potential vectors of AHSV and BTV in the areas studied in The Gambia. This prevalence suggests that these species may pose a risk to the health of local equines.
• The high seropositive rate of AHSV in Gambian horses and donkeys supports this suggestion, as it indicates that these animals have been exposed to the virus, potentially through Culicoides vectors.
• The ability of these midges to thrive in both early and late dry seasons further elevates their potential as a disease risk as it extends the potential transmission period of the viruses they carry.
• The absence of viruses in tested midges does not completely negate the potential transmission risk, as the presence of vector species and seropositive animals still suggests a likely exposure scenario.