Location: Foreign Arthropod Borne Animal Disease Research
Project Number: 3022-32000-062-016-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 22, 2025
End Date: Sep 21, 2028
Objective:
Vesicular stomatitis virus (VSV) is a centuries old pathogen that continues to cause economic loss in the United States. This loss primarily impacts farmers and ranchers, as symptomatic disease has been noted in horses, pigs, and cattle. The history of VSV disease in the US is one of recurring outbreaks that are eventually contained. Animal cases of infection consistent with vesicular stomatitis were described as early as the Civil War, in a report citing VS symptoms in army horses. Since that time, there have been many recognized outbreaks in the US. Throughout the 20th century, outbreaks impacting horses, cattle, and pigs were recognized. VSV-caused VS outbreaks in livestock have continued into the 21st century.
The cyclical nature of VSV appearance and disappearance in the US has meant that sustained investigation of VSV endemic sites, its vector hosts, and factors that determine its virulence in livestock remain understudied. This has left many questions about the pathogenesis, transmissibility, and vector competence of the virus unanswered. Recently, the commitment to the VSV Grand Challenge has provided an avenue to address some of these deficiencies, with positive results including initial work to model factors impacting VSV’s movement from other countries into the US, and some preliminary studies understanding factors that might impact VSV pathogenesis.
There are multiple possible explanations for why VSV virus sequences identified in different outbreaks do not follow a pattern predicted by standard evolutionary theory. One explanation is that the vector that initiates infection in livestock exerts a strong genetic bottleneck on the genome that can thrive in that vector. If this is the case, the genomic variance seen in different outbreaks would indicate that they were initiated by different vector hosts.
A second possible explanation for why VSV virus sequences identified in different outbreaks do not appear to follow classical evolutionary patterns is that wild-circulating VSV exists as a viral swarm with multiple different genotypes potentially able to initiate an outbreak or cause pathogenesis. There is tangential support for this second hypothesis from studies showing that direct culturing of VSV from animal lesions shows plaques of different sizes, indicating different genomes with different growth properties. In one example, an isolate of VSV Indiana, called small plaque variant 2 (S2) was isolated from lesion exudate. The S2 isolate shows an altered transcription gradient and more than 40 nucleotide changes from an isolate from the same exudate. This suggests that there are multiple viable genomes present in an outbreak situation. Our objective in this work is to examine each of these two possibilities for VSV genomic variation. To understand whether there is evidence that viral genome sequences can be impacted by different insect hosts.
Approach:
To understand whether there is evidence that viral genome sequences can be impacted by different insect hosts, we will passage VSV (NJ and Indiana) in cell lines from different insects. After several passages, we will collect viral RNA and sequence. We will compare the genome present in the passaged VSV to 1) determine mutations in the genome that have accumulated to consensus 2) the accumulation of subconsensus single nucleotide variants that suggest the rise of mixed viral populations and 3) estimate the size of the viral swarm following passage. We will compare these results with existing sequencing from recent and older outbreaks to determine whether we observe similar genomic changes.
To understand the second possibility - that there may be multiple replication competent viruses that circulate in an outbreak setting, we will take two separate tacks. For VSV Indiana, we will classify the S2 virus and its replication capacity on its own and paired with the San Juan isolates. This will be done both in mammalian and in insect cells to determine whether replication capacity changes in the different conditions.