Effect of Temperature on Replication of Epizootic Hemorrhagic Disease Viruses in Culicoides sonorensis (Diptera: Ceratopogonidae)

Replication of arboviruses, including orbiviruses, within the vector has been shown to be temperature dependent. Cooler ambient temperatures slow virus replication in arthropod vectors, whereas viruses replicate faster and to higher titers at warmer ambient temperatures. Previous research with epizootic hemorrhagic disease virus (EHDV) serotype 1 demonstrated that higher temperatures were associated with shorter extrinsic incubation periods in Culicoides sonorensis Wirth & Jones, a confirmed vector of EHDV in North America. To further our understanding of the effect of temperature on replication of EHDV within the vector, C. sonorensis were experimentally infected with one of three EHDV strains representing three serotypes (1, 2, and 7). Midges were fed defibrinated white-tailed deer (Odocoileus virginianus) blood spiked with EHDV (a parts per thousand yen10(6.5) TCID50/ml) through a parafilm membrane using an artificial feeding device and were then held at 20, 25, or 30A degrees C. In addition to this in vitro method, a white-tailed deer experimentally infected with EHDV-7 was used to provide an infectious bloodmeal to determine if the results were comparable with those from the in vitro feeding method. Whole midges were processed for virus isolation and titration at regular intervals following feeding; midges with a parts per thousand yen10(2.7) TCID50 were considered potentially competent to transmit virus. The virus recovery rates were high throughout the study and all three viruses replicated within C. sonorensis to high titer (a parts per thousand yen 10(2.7) TCID50/midge). Across all virus strains, the time to detection of potentially competent midges decreased with increasing temperature: 12-16 d postfeeding (dpf) at 20A degrees C, 4-6 dpf at 25A degrees C, and 2-4 dpf at 30A degrees C. Significant differences in replication of the three viruses in C. sonorensis were observed, with EHDV-2 replicating to a high titer in a smaller proportion of midges and with lower peak titers. The findings are consistent with previous studies of related orbiviruses, showing that increasing temperature can shorten the apparent extrinsic incubation period for multiple EHDV strains (endemic and exotic) in C. sonorensis.