The species composition and bio-ecology of Culicoides spp. frequenting livestock in the central Free State, South Africa

[摘要] English: Culicoides midges are involved in the transmission of a variety of pathogens, the most economically important of these are the orbiviruses that cause African horse sickness (AHSV) and bluetongue (BTV). The identification of vectors of these viruses and monitoring of their occurrence and activity plays an important role in the control measures and disease risk analysis. The primary tool used for monitoring these midges through collection is various models of light traps. In order to standardise collection data to be comparable between laboratories, a variety of factors that affect the light trap collections were assessed. Comparisons of different light traps (Onderstepoort trap and the Free State trap), the influence of light colour, trapping height and the distance a trap is operated from the host animals were assessed. Comparisons were done using either three replicates of a 4 x 4 or two replicates of a 6 x 6 randomised Latin square design. The most significant variables were the trap type, with the Onderstepoort trap collecting significantly more Culicoides than the Free State trap, and the sampling distance from the host animals. The proportion of C. imicola (the most frequent species collected) was the highest when collected right next to host animals and decreased rapidly as collections moved further from host animals. Trap height also proved to be an important variable, although no significant differences were observed when collecting midges at two metres to three metres above the ground. The occurrence, abundance and seasonality of the midges frequenting livestock in the central Free State were also assessed by collecting midges using light traps over a four-year period from April 2007 up to May 2010. Twenty Culicoides species were collected, the most abundant and important species was C. imicola, a confirmed vector of both the AHSV and BTV. The midges showed a distinct seasonal pattern, but were also collected year round, identifying periods of high risk, as well as a year-round risk of disease transmission. The midge populations almost disappeared when temperatures dropped during the winter months, the build-up and abundance during favourable conditions, however, indicated a high risk for disease transmission. Culicoides imicola also showed a considerable preference for livestock animals when assessing collections made near horses sheep and cattle as opposed to collections made in the absence of livestock host animals. An effort was made to identify possible breeding sites of Culicoides species. No midges were, however, collected in the tent type traps or the dung and soil samples collected and placed in emergence boxes. This again emphasised the diversity of the midges' breeding habitats and the enormous task still ahead to identify these sites to aid in possible reduction of midge numbers.

[发布机构] University of the Free State