Detection of vesicular stomatitis virus Indiana from insects collected during the 2020 outbreak in Kansas, USA

Authors: McGregor, Bethany; ROZO-LOPEZ, PAULA - Kansas State University; Davis, Travis; Drolet, Barbara

Submitted to: Pathogens
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2021
Publication Date: 9/2/2021
Citation: McGregor, B.L., Rozo-Lopez, P., Davis, T.M., Drolet, B.S. 2021. Detection of vesicular stomatitis virus Indiana from insects collected during the 2020 outbreak in Kansas, USA. Pathogens. 10(9):1126. https://doi.org/10.3390/pathogens10091126.
DOI: https://doi.org/10.3390/pathogens10091126

Interpretive Summary: Vesicular stomatitis virus (VSV) causes an economically important disease in horses, cattle, and pigs throughout the Americas that can be spread by infected insects. Outbreaks usually occur in the western and southwestern United States on a 5-10 year cycle and can result in significant financial losses due to animal movement restrictions and health impacts to infected animals. In 2019-2020, a large outbreak of VSV occurred with positive cases reaching as far east as Kansas and Missouri. The insect species responsible for spread of VSV in these states is poorly studied because VS outbreaks are very rare, but in other parts of the country, biting midges and black flies are known to transmit the virus. In this study, insects on two farms with confirmed VSV-positive horses were collected and tested for VSV. Three biting midge species pools and one black fly species were positive for virus. Some of the VSV-positive midges had never taken a previous blood meal. This is important since taking a first blood meal is how most insects pick up viruses. Based on this information, it is possible that either transmission is occurring from mother to offspring or sexual transmission of this virus is happening during mating. This has never been shown in wild populations and could be an important way that this virus may be maintained through winter periods. This is also the first report of field detections of this type of VSV from two of the species. Overall this study helps us better understand VSV outbreaks in the central part of the United States and improves our ability to detect and control target insect species and outbreaks in the future.

Technical Abstract: 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. 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 VSV-IN RNA by RT-qPCR. 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.