While vesicular stomatitis virus (VSV) is rarely fatal, it does cause physical discomfort in livestock, reduces production efficiency and may result in serious secondary infections. In addition, the clinical signs in cattle and pigs are similar to those of foot-and-mouth disease, so every outbreak must be closely monitored.
Endemic in Mexico and breaking sporadically in the U.S., new research from USDA Agricultural Research Service (ARS) scientists could help prevent the spread of VSV. Wyoming researchers Barbara Drolet at the Arthropod-Borne Animal Diseases Research Laboratory (ABADRL) in Laramie and Justin Derner at the ARS High Plains Grasslands Research Station in Cheyenne have shown that, under lab conditions, rangeland plants can harbor VSV and pass the virus to grasshoppers feeding on them. Though there are no reports to date of field rangeland-plant testing during outbreaks, the scientists showed that a common grasshopper pesticide also kills the virus on the plants.
Infected animals salivate heavily, shedding virus in the saliva, which results in animal-to-animal transmission. During an outbreak, producers try to control the spread of VSV by restricting animal movement, disinfecting all materials used, and limiting the animals’ exposure to insects that transmit the virus.
Soil and plants have been thought to be VSV sources, but this hasn’t been previously confirmed. Thus, current recommendations for VSV control don’t include decontamination of corral soils and pastures.
Previous research by ABADRL and University of Wyoming scientists showed that, in grasshoppers, the virus can multiply and then infect cattle that eat the insects while grazing. That study prompted Drolet to investigate that if infected animals shed the virus onto pasture plants as they graze, can the virus remain infectious on the plant surface? And if so, will grasshoppers become infected by eating contaminated plants?
To determine the window of opportunity for grasshoppers to ingest viable VSV from contaminated plants, Drolet and Derner selected 14 rangeland plant species that grasshoppers eat, exposed the plants to VSV in a laboratory setting, and measured virus survival over time.
“Several plant species harbored viable virus up to 24 hours in the lab,” Drolet says. This is the first report demonstrating the stability of VSV on rangeland-plant surfaces.
The scientists then exposed two of the plant species to VSV and fed them to grasshoppers 24 hours later. The grasshoppers became infected, which supports the hypothesis that grasshopper-cattle-grasshopper transmission of VSV is possible.
The scientists next tested a common grasshopper pesticide and found it could deliver a double punch if used during an outbreak in pastured animals: In addition to reducing the grasshopper population, the pesticide inactivated VSV on contact, thus potentially reducing a source of virus for grazing animals and any remaining grasshoppers.
“We haven’t investigated the molecular mechanisms behind it,” Drolet says. “But the results clearly show that this pesticide is lethal to VSV.”
The report was published in the May issue of Applied and Environmental Microbiology. See it at aem.asm.org/cgi/content/.
-- ARS release