Identical viral genetic sequence found in black flies (Simulium bivittatum) and the equine index case of the 2006 U.S. vesicular stomatitis outbreak

Authors: Drolet, Barbara; Reeves, Will; BENNETT, KRISTINE - Colorado State University; Pauszek, Steven; Bertram, Miranda; Rodriguez, Luis

Submitted to: Pathogens
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2021
Publication Date: 7/23/2021
Citation: Drolet, B.S., Reeves, W.K., Bennett, K.E., Pauszek, S.J., Bertram, M.R., Rodriguez, L.L. 2021. Identical viral genetic sequence found in black flies (Simulium bivittatum) and the equine index case of the 2006 U.S. vesicular stomatitis outbreak. Pathogens. 10(8):929-938. https://doi.org/10.3390/pathogens10080929.
DOI: https://doi.org/10.3390/pathogens10080929

Interpretive Summary: Vesicular stomatitis virus is transmitted by insects and causes vesicular disease in U.S. cattle, horses and swine. Outbreaks occur sporadically every 5-10 years and can result in single year or multi-year outbreak patterns. The 2004 - 2006 outbreak caused disease in both horses and cattle for three summers in a row. In the third outbreak year (2006), biting flies and grasshoppers were collected near three positive premises with infected horses in Natrona County, WY to determine which insect species may be playing a role in the re-emergent outbreak. After testing over 12,000 insects, we detected VSV in two pools of female black flies. When sequenced, the virus RNA was a 100% match to the infected horse at the premises. This is the first field evidence of possible black fly maintenance of VSV during an outbreak.

Technical Abstract: In 2006, vesicular stomatitis New Jersey virus (VSNJV) caused outbreaks in Wyoming (WY) horses and cattle after overwintering in 2004 and 2005. Within two weeks of the outbreak onset, 12,203 biting flies and 194 grasshoppers were collected near three equine-positive premises in Natrona County, WY. Insects were identified to the species level and tested by RT-qPCR for VSNJV polymerase (L) and phosphoprotein (P) gene RNA. Collected dipterans known to be competent for VSV transmission included Simulium black flies and Culicoides biting midges. VSNJV L and P RNA was detected in two pools of female Simulium bivittatum and subjected to partial genome sequencing. Phylogenetic analysis based on the hypervariable region of the P gene from black flies showed 100% identity to the isolate obtained from the index horse case on the same premises. This is the first report of VSNJV in S. bivittatum in WY and the first field evidence of possible VSV maintenance in black fly populations during an outbreak.