The oral susceptibility of South African livestock-associated Culicoides species to selected orbiviruses

[摘要] English: Culicoides (Diptera, Ceratopogonidae) midges play an essential role in transmittingorbiviruses. Recent outbreaks of bluetongue (BT) in Europe highlighted the risk forintroduction and rapid spread of vector-borne diseases outside their traditionalboundaries, and increase international interest in arbovirus epidemiology. Africanhorse sickness virus (AHSV) and bluetongue virus (BTV) cause diseases of highsocio-economic impact, especially on international trade. Identifying potentialvectors is crucial for the implementation of integrated control measures, disease riskanalysis and management. Determination of oral susceptibility of Culicoides speciesto infection with orbiviruses provides valuable data for assessing vector competence.The aim of this work was to 1) determine oral susceptibility of livestockassociated midges to infection with wild-type and live-attenuated strains of BTV andAHSV; 2) evaluate the efficiency of different light sources for the collection ofCulicoides species; 3) compare laboratory blood-feeding methods; 4) identifypotential vectors and 5) determine field infection prevalence in Culicoides species inthe winter rainfall region of South Africa during an outbreak of AHS.Although black light collection did not have any influence on the agegradingdetermination of a Culicoides population, it was more effective than whitelight for the collection of adult Culicoides midges. Cotton wool feeding yieldedlower infection rates than membrane feeding due to the greater blood meal size takenby Culicoides females fed through the latter. Virus recovery of reference and vaccinestrains of BTV was higher in Culicoides bolitinos than in Culicoides imicola. Therewas no significant difference between the oral susceptibility of C. bolitinos andC.-imicola for the various AHSV isolates used. Virus recovery of the vaccine strainof AHSV serotype 7 (AHSV-7) from C. imicola at Onderstepoort was higher thanthat of the field strains of AHSV-7. Culicoides imicola from the eastern Free State was more susceptible to AHSV than in Gauteng. Both BTV and AHSV wererecovered from non-Avaritia Culicoides species. These results indicate BT and AHSto be multi vector diseases and add to the complexity of the epidemiology oforbiviruses. True assessment of vector competence might be difficult to assess if itwould require some level of real-time monitoring, e.g. testing local Culicoidespopulations using variants of orbiviruses in current circulation.Light trap surveys in the winter rainfall area of South Africa during anoutbreak of AHSV demonstrated that C. imicola is superabundant and occurs innumbers to be equal or even higher than that in the summer rainfall areas. Results oforal susceptibility studies and the recovery of different orbiviruses, indicate thispopulation of C. imicola to be highly vector competent.

[发布机构] University of the Free State