EHDV-2 Infection Prevalence Varies in Culicoides sonorensis after Feeding on Infected White-Tailed Deer over the Course of Viremia

Abstract

Epizootic hemorrhagic disease viruses (EHDVs) are arboviral pathogens of white-tailed deer and other wild and domestic ruminants in North America. Transmitted by various species of Culicoides, EHDVs circulate wherever competent vectors and susceptible ruminant host populations co-exist. The impact of variation in the level and duration of EHDV viremia in white-tailed deer (Odocoileus virginianus) on Culicoides infection prevalence is not well characterized. Here we examined how infection prevalence in a confirmed North American vector of EHDV-2 (Culicoides sonorensis) varies in response to fluctuations in deer viremia. To accomplish this, five white-tailed deer were experimentally infected with EHDV-2 and colonized C. sonorensis were allowed to feed on deer at 3, 5, 7, 10, 12, 14, 18, and 24 days post infection (dpi). Viremia profiles in deer were determined by virus isolation and titration at the same time points. Blood-fed Culicoides were assayed for virus after a 10-day incubation (27 °C) period. We found that increases in deer EHDV blood titers significantly increased both the likelihood that midges would successfully acquire EHDV and the proportion of midges that reached the titer threshold for transmission competence. Unexpectedly, we identified four infected midge samples (three individuals and one pool) after feeding on one deer 18 and 24 dpi, when viremia was no longer detectable by virus isolation. The ability of ruminants with low-titer viremia to serve as a source of EHDV for blood-feeding Culicoides should be explored further to better understand its potential epidemiological significance.

Keywords: Culicoides sonorensis; Odocoileus virginianus; epizootic hemorrhagic disease virus; hemorrhagic disease; orbivirus; white-tailed deer.

Figure 1

Viremia profiles spanning from 0 days post infection (dpi) to 18 dpi are plotted alongside midge infection prevalence for individual deer in the trial (a–e). A dotted line at 2.3 on the primary y-axis of each graph indicates the limit of detection for viral titer. Midge infection data for deer 5, 5 dpi and deer 4, 7 dpi have been omitted from their respective graphs due to contamination of samples during virus isolation.

Figure 2

Mean epizootic hemorrhagic disease virus serotype 2 titer of viremic deer and proportion of infected midges determined by pooling data from all 5 deer for each time point. Standard error bars are shown for both mean deer viremia and midge infection prevalence. A lack of standard error bars indicates no variation in values observed. The dotted line at 2.3 on the primary y-axis indicates the limit of detection for blood virus titer (10^2.3 tissue culture infective dose (TCID)₅₀/mL).

Figure 3

Evaluation of cell lines for EHDV diagnostics. Virus isolation from blood of deer was attempted on three different cell lines at different time points throughout the study. Shaded cells indicate positive virus isolation.

Figure 4

Bar graph showing proportion of epizootic hemorrhagic disease virus serotype 2 positive midges that reached titers > 10^2.7 median tissue culture infective doses (TCID₅₀)/midge and were considered competent to transmit virus. No positive midges were detected at 12 dpi.

Figure 5

Plot showing titration values from all EHDV-2 positive midges. Each point on the graph represents a single midge. Horizontal bars indicate the mean titer while vertical bars reflect standard deviation. On the y-axis, the solid line at 2.7 denotes the threshold of transmission competence (10^2.7 TCID₅₀/midge) and the dotted line at 2.3 denotes the limit of detection (10^2.3 TCID₅₀/midge).