ARS | Publication request: Vector competence of Culicoides sonorensis (Diptera: Ceratopogonidae) to epizootic hemorrhagic disease virus serotype 7

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 2012
Publication Date: October 17, 2012
Repository URL: http://www.parasitesandvectors.com/content/pdf/1756-3305-5-236.pdf
Citation: Ruder, M.G., Howerth, E.W., Stallknecht, D.E., Allison, A.B., Carter, D.L., Drolet, B.S., Klement, E., Mead, D.G. 2012. Vector competence of Culicoides sonorensis for epizootic hemorrhagic disease virus serotype 7. Parasites & Vectors. 5:248.

Interpretive Summary: The biting midge is widely distributed in the U.S. and is the only known insect to transmit the viruses that cause epizootic hemorrhagic disease in white-tailed deer and cattle. Of the seven proposed epizootic hemorrhagic disease virus (EHDV) types, only three are currently present in the U.S. (domestic types), and four are exotic. One exotic type that caused widespread disease among Israeli dairy cattle herds was recently shown experimentally to cause disease in our white-tailed deer. This indicates that if this exotic virus were to be introduced into the U.S., our white-tailed deer populations would be severely affected and the virus could become established if we have the insects to transmit this virus. The study described here was done to determine if U.S. midges could become infected by this exotic type of EHDV and whether it could then transmit the virus to our white-tailed deer, resulting in widespread outbreaks. The results of the study showed that our biting midge species is, in fact, susceptible to infection and can transmit the virus between white-tailed deer. These findings are useful to diagnosticians, veterinarians, researchers, cattle producers, wildlife professionals and others involved in livestock and wildlife health and management.

Technical Abstract: Background: Culicoides sonorensis (Diptera: Ceratopogonidae) is a vector of epizootic hemorrhagic disease virus (EHDV) serotypes 1 and 2 in North America, where these viruses are well-known pathogens of white-tailed deer (WTD) and other wild ruminants. Although historically rare, reports of clinical EHDV infection in cattle have increased in some parts of the world over the past decade. In 2006, an EHDV-7 epizootic in cattle resulted in economic loss for the Israeli dairy industry. White-tailed deer are susceptible to EHDV-7 infection and disease; however, this serotype is exotic to the US and the susceptibility of C. sonorensis to this cattle-virulent EHDV is not known. The objective of the study was to determine if C. sonorensis is susceptible to EHDV-7 infection and can is a competent vector. Methods: To evaluate the susceptibility of C. sonorensis, midges were fed on WTD experimentally infected with EHDV-7, held at 22 ± 1 °C, and processed individually for virus isolation and titration on 4-16 days post feeding (dpf). Midges with a virus titer of =102.7 median tissue culture infective doses (TCID50)/midge were considered potentially competent. To determine if infected C. sonorensis were capable of transmitting EHDV-7 to a host, a susceptible WTD was then fed on by a group of 14-16 dpf midges. Results: From 4-16 dpf, 45% (156/350) of midges that fed on WTD with high titer viremia (>107 TCID50/ml) were virus isolation-positive, and beginning 10-16 dpf, 32% (35/109) of these virus isolation-positive midges were potentially competent (=102.7 TCID50/midge). Midges that fed on infected deer transmitted the virus to a susceptible WTD at 14-16 dpf. The WTD developed viremia and severe clinical disease. Conclusion: This study demonstrates that C. sonorensis is susceptible to EHDV-7 infection and can transmit the virus to susceptible WTD, thus, C. sonorensis should be considered a potential vector of EHDV-7. Together with previous work, this study demonstrates that North America has a susceptible ruminant and vector host for this exotic, cattle-virulent strain of EHDV-7.