Detection of Vesicular Stomatitis Virus Indiana from Insects Collected during the 2020 Outbreak in Kansas, USA

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.

Surveillance along the Rio Grande during the 2020 Vesicular Stomatitis Outbreak Reveals Spatio-Temporal Dynamics of and Viral RNA Detection in Black Flies

“…To our knowledge, we are making the first report of VSV detected in Simulium collected in habitats outside of farms and ranches with concurrent or historical epizootics of the virus. Additionally, this is the first detection of VSIV in Simulium in NM; we note that VSIV was also detected in 2020 from S. meridionale collected on a VSIV-confirmed premise in Kansas [20]. VSNJV has previously been detected in S. vittatum and S. bivittatum during outbreaks [17,21].…”

“…Multiple methods for detecting virus or viral genome have been used to identify vectors potentially involved in the VSV transmission cycle. These methods have detected VSV or its genome in hematophagous dipterans including Simuliidae (black flies) [17][18][19][20][21], Psychodidae (sand flies) [22], Ceratopogonidae (biting midges) [20,23], and Culicidae (mosquito) vectors [24]; as well as non-hematophagus dipterans including houseflies, (Muscidae), root-maggot flies (Anthomyiidae), and eye gnats (Chloropidae) [17,19]. The majority of VSV detections in insects have occurred on farms and ranches during concurrent VSV outbreaks.…”

A Review of the Vector Status of North American Culicoides (Diptera: Ceratopogonidae) for Bluetongue Virus, Epizootic Hemorrhagic Disease Virus, and Other Arboviruses of Concern

“…Elucidation of natural VSV cycles is difficult due to the sporadic nature of outbreaks, and numerous insect species have been implicated in both mechanical and biological transmission [7]. VSV has been detected in field-collected C. sonorensis from past US outbreaks, including the 2019-2020 outbreak, which affected animals in states from Arkansas to Arizona [19]. Interestingly, there is evidence that VSV may be transmitted transovarially [20] and/or venereally [21] between midges, which has not been shown in Orbiviruses.…”

“…Tabachnick [12] refers to some of his unpublished data on infection rates in field-collected C. variipennis from New York, New Jersey, and Maryland, and C. occidentalis from California, where they found low (< 3%) minimum BTV infection rates. More recently, McGregor et al [19] reported a single VSV + pool of C. variipennis collected in Kansas during the 2020 outbreak. To date, no laboratory infection experiments using C. variipennis have been conducted, so the true vector competence of this species for any of the Culicoides-transmitted arboviruses is unknown.…”

“…This species has broad larval habitat associations including along stream and pond edges, as well as small puddles, pools, swamps, and springs [3]. Several arboviruses have been detected from field-collected C. stellifer, including EHDV-2, EHDV-6, and BTV (serotype unspecified) in Florida [16•], BTV-12 in Louisiana [17,18], VSV-Indiana serotype in Kansas [19], VSV-New Jersey serotype in Colorado [36], and West Nile virus in Louisiana [37]. This small species has proven particularly challenging to work with in the laboratory, yielding few successful laboratory vector competence assays.…”