Effect of temperature on replication of epizootic hemorrhagic disease viruses in Culicoides sonorensis (Diptera: Ceratopogonidae)

Authors: Ruder, Mark; STALLKNECHT, DAVID - University Of Georgia; HOWERTH, ELIZABETH - University Of Georgia; CARTER, DEBORAH - University Of Georgia; Pfannenstiel, Robert; ALLISON, ANDREW - Cornell College - Iowa; MEAD, DANIEL - University Of Georgia

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2015
Publication Date: 9/1/2015
Citation: Ruder, M.G., Stallknecht, D.E., Howerth, E.W., Carter, D.L., Pfannenstiel, R.S., Allison, A.B., Mead, D.G. 2015. Effect of temperature on replication of epizootic hemorrhagic disease viruses in Culicoides sonorensis (Diptera: Ceratopogonidae). Journal of Medical Entomology. 52(5):1050-1059.

Interpretive Summary: Epizootic hemorrhagic disease (EHD) is a viral disease of wild and domestic ruminants transmitted by small insects known as Culicoides biting midges. Seasonal EHD outbreaks typically occur in the United States during the warmer months of late summer and early autumn. For many viral diseases transmitted by insects, including EHD, replication of the virus within the insect host has been shown to depend on temperature. In general, cooler ambient temperatures slow virus replication in insect vectors, whereas viruses replicate faster and to higher titers at warmer ambient temperatures. This becomes important when trying to understand disease transmission from animal-to-animal by the insect vector during different environmental conditions. In order to better understand EHDV replication within the Culicoides vector, we experimentally infected Culicoides sonorensis with EHDV and held the insects at three different temperatures (20°C, 25°C, 30°C) during the incubation period. Three different virus serotypes were evaluated. Across all three EHDV serotypes, the time it took for virus replication to reach levels high enough for potential virus transmission to a host decreased with increasing temperature.

Technical Abstract: Replication of many arboviruses, including some orbiviruses, within the vector has been shown to be temperature-dependent. In general, 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, a confirmed vector a EHDV in North America. In order 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 serotypes (1, 2, and 7). Midges were fed defibrinated white-tailed deer (Odocoileus virginianus) blood spiked with EHDV (=106.5 TCID50/ml) through a parafilm membrane using an artificial feeding device and were then held at 20, 25, or 30 °C. In addition to this in vitro method, a white-tailed deer experimentally infected with EHDV-7 was used to provide an infectious blood meal to determine if the results were comparable to those from the in vitro feeding method. Whole midges were processed for virus isolation and titration at regular intervals; midges with = 102.7 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 (= 102.7 TCID50/midge). Across all serotypes, the time to detection of potentially competent midges decreased with increasing temperature: 12-16 days post feeding (dpf) at 20 °C, 4-6 dpf at 25 °C, and 2-4 dpf at 30 °C. The findings are consistent with previous studies of related orbiviruses, showing that increasing temperature can shorten the apparent extrinsic incubation period for multiple EHDV serotypes (endemic and exotic) in C. sonorensis.