Grasshoppers Transmit Virus To Livestock
According to a published research study by Agricultural Research Service (ARS) scientists, rangeland plants could be harboring the vesicular stomatitis virus (VSV) that grasshoppers are transmitting to cattle, horses, and other hoofed animals.
VSV, which resembles foot-and-mouth disease when it occurs in cattle, is a viral disease that causes sporadic outbreaks in the U.S. For the past two decades, VSV has caused disease outbreaks in the western U.S. every two to nine years, with the most recent one in 2009.
Barbara Drolet at the ARS Arthropod-Borne Animal Diseases Research Laboratory in Laramie, Wyoming, and Justin Derner at the ARS High Plains Grasslands Research Station in Cheyenne, Wyoming, proved that under laboratory conditions, rangeland plants can harbor VSV and pass the virus to grazing grasshoppers.
"The first grasshopper-cattle-grasshopper VSV transmission research, published in 2003, was based on two major assumptions:
1. Virus shed from clinically infected animals on pasture plants would remain infectious on the plant surfaces.
2. Grasshoppers would become infected by eating the virally contaminated plants.
The goal of this study was to determine if either of these assumptions were true in a laboratory setting," says Drolet.
To determine the window of opportunity for grasshoppers to ingest viable VSV from contaminated plants, Drolet and Derner selected 14 rangeland plant species grasshoppers eat and exposed plants to VSV in a lab setting. Several species harbored viable virus for up to 24 hours.
The scientists then exposed two plant species to VSV and fed them to grasshoppers 24 hours later. The grasshoppers became infected. These results support the premise that grasshopper-cattle-grasshopper transmission of VSV is possible.
"We hope to someday collect grasshoppers where an active outbreak is occurring and test them for virus. If VSV is detected, that will provide field evidence for what we are seeing in the laboratory," says Drolet.
The scientists next tested a common grasshopper pesticide and found that -- in addition to reducing the grasshopper population -- upon contact, the pesticide inactivated VSV, which reduced a source of virus for livestock and grasshoppers.
Use of the tested, or similar, pes-ticide to inactivate virus during outbreaks would require additional U.S. EPA registration.
Even though the disease is rarely fatal, VSV causes painful blisters in the mouth and on the dental pad, tongue, lips, nostrils, hooves, and teats of animals. Once introduced into a herd, the disease seems to move from animal to animal by contact or exposure to saliva or fluid from ruptured blisters.
The results of this study could be helpful in making disease-management decisions during future outbreaks, not only by offering a potential method of control, but also by making it possible to more accurately assess a herd's risk.