Comparison of endemic and epidemic vesicular stomatitis virus lineages in Culicoides sonorensis midges

Authors: ROZO-LOPEZ, PAULA - Kansas State University; Pauszek, Steven; Velazquez, Lauro; Rodriguez, Luis; PARK, YOONSEONG - Kansas State University; Drolet, Barbara

Submitted to: Viruses
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2022
Publication Date: 6/3/2022
Citation: Rozo-Lopez, P., Pauszek, S.J., Velazquez Salinas, L., Rodriguez, L.L., Park, Y., Drolet, B.S. 2022. Comparison of endemic and epidemic vesicular stomatitis virus lineages in Culicoides sonorensis midges. Viruses. 14(6):1221-1233. https://doi.org/10.3390/v14061221.
DOI: https://doi.org/10.3390/v14061221

Interpretive Summary: Vesicular stomatitis virus (VSV) is transmitted by biting midges and causes disease in cattle, horses and swine. VSV is endemic in Mexico and spreads north into the US sporadically every 5-10 years. Many questions remain as to what animal, insect, and environmental conditions allow these as yet unpredictable incursions into the US. In 2012, one strain of VSV (epidemic 1.1) escaped Mexico and caused significant disease in US cattle and horses. Another virus that was genetically very similar (endemic 1.2) remained in Mexico and did not move northward into the US. Previous studies found that the epidemic 1.1 virus caused more severe disease in pigs compared to the endemic 1.2 strain that did not move north to the US. In this follow-up study, we found that the epidemic 1.1 strain also caused more infection in biting midges than the endemic 1.2 strain. We propose that there are specific genetic changes in some VSV strains which allow them to escape endemic regions of Mexico and spread northward into the US to cause outbreaks. These viruses cause more infection in animals so they are more likely to be ingested by blood-feeding midges, and they cause more infection in the midges so they are more likely to be transmitted to other animals when midges feed again.

Technical Abstract: Vesicular stomatitis virus (VSV) primarily infects livestock and is transmitted by direct contact and vectored by Culicoides midges (Diptera: Ceratopogonidae). Endemic to Central and South America, specific VSV lineages spread northward out of endemic regions of Mexico and into the U.S. sporadically every five to ten years. In 2012, a monophyletic epidemic lineage 1.1 successfully spread northward into the U.S. In contrast, the closest endemic ancestor, lineage 1.2, remained circulating exclusively in endemic regions in Mexico. It is not clear what roles virus-animal interactions and/or virus-vector interactions play in the ability of specific viral lineages to escape endemic regions in Mexico and successfully cause outbreaks in the U.S., nor the genetic basis for such incursions. Whole-genome sequencing of epidemic VSV 1.1 and endemic VSV 1.2 revealed significant differences in just seven amino acids. Previous studies in swine showed that VSV 1.1 was more virulent than VSV 1.2. Here, we compared the efficiency of these two viral lineages to infect the vector Culicoides sonorensis (Wirth and Jones) and disseminate to salivary glands for subsequent transmission. Our results showed that midges orally infected with the epidemic VSV 1.1 lineage had significantly higher infection dissemination rates compared to those infected with the endemic VSV 1.2 lineage. Thus, in addition to affecting virus-animal interactions, as seen with higher virulence in pigs, small genetic changes may also affect virus-vector interactions, contributing to the ability of specific viral lineages to escape endemic regions via vector-borne transmission.