Infection of grasshoppers following ingestion of grassland plant species harboring vesicular stomatitis virus

Authors: Drolet, Barbara; Derner, Justin

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/13/2008
Publication Date: 7/13/2008
Citation: Drolet, B.S., Derner, J.D. 2007. Infection of grasshoppers following ingestion of grassland plant species harboring vesicular stomatitis virus. Meeting Abstract.

Interpretive Summary: Vesicular stomatitis virus (VSV) causes sporadic, re-emerging disease outbreaks in horses and cattle in the western United States. Clinically infected animals shed large amounts of virus in their saliva contaminating their surroundings and resulting in efficient spread of the virus within the herd. Virus contaminates equipment, personnel and the general area where clinically infected animals are located. Currently, control and prevention recommendations include disinfecting corrals, feed and water troughs, personnel gear, and premise equipment and vehicles, with no recommendations for pasture soils or plants. Although research emphasis has traditionally focused on blood feeding insects as transmission vectors for VSV, a migratory grasshopper has been shown to be an efficient amplifying reservoir and possible mechanical vector for VSV. We have shown that some grassland plant species, found in western U.S. cattle pastures and known to be eaten by these native and abundant grasshoppers, were capable of harboring significant titers of virus for up to 24 hours post exposure (hpe). To determine the significance of VSV survivability in this transmission model, grasshoppers were allowed to feed on virus exposed plants at 24 hpe, and held for 3 weeks. Virus isolation and PCR results show that grasshoppers can become infected following ingestion of these virus contaminated plant sources. This suggests that plant species in pastures with salivating, clinically infected livestock may be sources of infection for these amplifying reservoir insects for up to 24 hours after the last clinically infected animal is removed. A possible method of grasshopper disinfestation, with consequent decontamination of pasture plants, is discussed.

Technical Abstract: Vesicular stomatitis virus (VSV) causes sporadic, re-emerging disease outbreaks in horses and cattle in the western United States. Lesions in the oral cavity result in excessive salivation and significant virus shedding. This results in efficient direct contact transmission within the herd, and viral contamination of equipment and general area where clinically infected animals are located. Although soils and plants are often suggested as possible virus sources, no previous reports confirm this. Currently, control and prevention recommendations by animal health or regulatory officials include disinfecting corrals, feed and water troughs, personnel gear, and premise equipment and vehicles, with no recommendations for pasture soils or plants. Insects are believed to play important roles in the initial introduction of the virus into the herd, as well as transmission between animal herds. Although research emphasis has traditionally focused on blood feeding insects as transmission vectors, a migratory grasshopper has been shown to be an efficient amplifying reservoir and possible mechanical vector for VSV. We previously investigated whether typical grassland plant species, found in western U.S. cattle pastures and known to be eaten by these native and abundant grasshoppers, were capable of sustaining virus for significant amounts of time. We found that while no virus replication was observed in any plant species tested, several were capable of harboring significant titers of virus for up to 24 hours post exposure (hpe). To determine the significance of VSV survivability in this transmission model, grasshoppers were allowed to feed on virus exposed plants at 24 hpe, and held for 3 weeks. Virus isolation and PCR results show that grasshoppers can become infected following ingestion of these virus contaminated plant sources. This suggests that plant species in pastures with salivating, clinically infected livestock may be sources of infection for these amplifying reservoir insects for up to 24 hours after the last clinically infected animal is removed. A possible method of grasshopper disinfestation, with consequent decontamination of pasture plants, is discussed.