<p>Vesicular stomatitis (VS) is a reportable viral disease which affects horses, cattle, and pigs in the Americas. Outbreaks of vesicular stomatitis virus New Jersey serotype (VSV-NJ) in the United States typically occur on a 5–10-year cycle, usually affecting western and southwestern states.</p>
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<p>In 2019–2020, an outbreak of VSV Indiana serotype (VSV-IN) extended eastward into the states of Kansas and Missouri for the first time in several decades, leading to 101 confirmed premises in Kansas and 37 confirmed premises in Missouri. In order to investigate which vector species contributed to the outbreak in Kansas, we conducted insect surveillance at two farms that experienced confirmed VSV-positive cases, one each in Riley County and Franklin County. Centers for Disease Control and Prevention miniature light traps were used to collect biting flies on the premises. Two genera of known VSV vectors, Culicoides biting midges and Simulium black flies, were identified to species, pooled by species, sex, reproductive status, and collection site, and tested for the presence of VSVIN RNA by RT-qPCR. </p>
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<p>In total, eight positive pools were detected from Culicoides sonorensis (1), Culicoides stellifer (3), Culicoides variipennis (1), and Simulium meridionale (3). The C. sonorensis- and C. variipennis-positive pools were from nulliparous individuals, possibly indicating transovarial or venereal transmission as the source of virus. This is the first report of VSV-IN in field caught C. stellifer and the first report of either serotype in S. meridionale near outbreak premises. These results improve our understanding of the role midges and black flies play in VSV epidemiology in the United States and broadens the scope of vector species for targeted surveillance and control.</p>
We identified four species of biting Diptera that were positive for VSV-IN during the 2020 expansion into Kansas: C. sonorensis, C. stellifer, C. variipennis, and S. meridionale. Calculated infection rates for these species were variable, with the greatest rates calculated in S. meridionale and C. stellifer and the lowest rates in C. variipennis. Each of these species represents unique biology and ecology that must be considered when optimizing control and surveillance strategies moving forward. This is also the first field detection of VSV-IN-positive nulliparous individuals indicating transovarial or venereal transmission outside of a laboratory environment. These data contribute substantially to our knowledge of the epidemiology of VSV-IN in the U.S. and will improve our ability to conduct targeted surveillance and control of vector species in the event of continued outbreaks.