The Culicoides enigma: which biting midge species are important in the epidemiology of hemorrhagic disease in the Southeast?

Hemorrhagic disease (HD) of white-tailed deer (WTD; Odocoileus virginianus) is caused by epizootic hemorrhagic disease viruses (EHDV) or bluetongue viruses (BTV). Confirmed vectors include C. sonorensis (BTV and EHDV) and C.... [ view full abstract ]

Hemorrhagic disease (HD) of white-tailed deer (WTD; Odocoileus virginianus) is caused by epizootic hemorrhagic disease viruses (EHDV) or bluetongue viruses (BTV). Confirmed vectors include C. sonorensis (BTV and EHDV) and C. insignis (BTV only) but in endemic regions of the Southeast, other Culicoides species are suspected vectors. SCWDS is actively engaged in long-term monitoring of both Culicoides populations and HD activity in the Southeast. Collectively, these datasets can be used to better understand patterns of disease and recognize gaps in our understanding of HD epidemiology. From 2007-2015, adult Culicoides were collected August-September using CDC miniature black-light traps at 272 sites (>7,000 trap nights) throughout WTD habitat in the Southeast (AL, AR, FL, GA, LA, MS, NC, SC, and TN). In addition to Culicoides surveys, HD activity in the same study region was monitored by annual HD reporting by state wildlife management agencies using a questionnaire-based survey, along with diagnostic virology to isolate EHDV and BTV from WTD suspected to have HD. From 2007-2015, HD was reported annually in most states within the study region and 143 viruses (3 EHDV serotypes and 6 BTV serotypes) were isolated from dead WTD. Culicoides surveys in the same region over the nine year study period yielded nearly 300,000 Culicoides, representing 44 species. C. insignis, a BTV vector, was commonly collected in FL (present at 77% of sites) but was scarce outside of FL (present at 9% of sites). C. sonorensis (EHDV/BTV vector) was rarely recovered and was only present in 5% of sites in low numbers. Commonly collected Culicoides spp. (present at >45% of sites) over the entire survey area were C. haematopotus, C. stellifer, and C. debilipalpis. Absence of confirmed vectors throughout much of the study area, a region with endemic HD activity, indicates need for targeted studies aimed at incriminating suspect vectors.