Summer and fall are the times of year when many livestock producers participate in fairs, exhibitions and shows. However, it is not the time to be lax about biosecurity measures given the ongoing risks of commingling animals at these events. An outbreak of vesicular stomatitis (VS) in the southwestern region of the United States was confirmed on June 21, 2019 by the National Veterinary Services Laboratories (NVSL). The first case was on a horse farm in Kinney County, Texas. Since then the outbreak has spread across Colorado, Nebraska, New Mexico, Oklahoma, Texas, Utah, and Wyoming. The U.S. Department of Agriculture, Animal and Plant Health Inspection Service (USDA APHIS) confirmed that the horses on these premises showed clinical signs and tested positive for VS. Horses and other livestock being hauled to and from exhibitions may contribute to spreading this highly contagious disease.
Vesicular stomatitis is the most common vesicular disease of livestock in the United States, Mexico, Central, and South America. The causative virus was first isolated in 1925 (Lambert, T., Leedom Larson, K.R., 2016), but signs have been reported since the 1800s. In warmer regions of the Americas, VS is considered an endemic disease of livestock. Although livestock can recover from this disease, it is important to know what the signs are and how to prevent it.
The disease is caused by a virus that has two serotypes (separate groups within a species of microorganisms that all share a similar characteristic): the New Jersey and the Indiana serotypes. The New Jersey serotype is responsible for the 2019 outbreak. Both types of VS have been seen sporadically throughout the disease’s history, with the largest outbreak affecting nine states in 2005 (Traub-Dargatz, J., & Pelzel-McCluskey, A., n.d. ). The 2019 U.S. outbreak is nearly as extensive, reaching the seven states mentioned above, and spreading to 1,078 premises as of the USDA September 26, 2019 VS report. The disease is reportable, meaning that when diagnosed it must be reported directly by a producer, the herd veterinarian or the state veterinarian to the USDA APHIS Veterinary Services.
Primarily a disease of horses, cattle and swine, VS can also be found in sheep, goats, llamas and alpacas. It is seasonal, appearing during the warmer seasons and disappearing during the winter. Blood sucking insect vectors such as black flies, sand flies and midges transmit the disease to livestock (Traub-Dargatz, J., & Pelzel-McCluskey, A., n.d.). The virus can spread between animals through direct contact with infected animals, or from exposed equipment (fomites) including buckets, feed, trailers or manure. It is considered a zoonotic disease that on rare occasions can infect humans after handling infected animals, resulting in flu-like symptoms.
The incubation period for VS is two to eight days before an animal develops any signs of infection. Clinical signs consist of:
- Sores on the tongue, mouth lining, nose, lips, coronary bands, udder or sheath.
- Drooling or frothing at the mouth.
- Reluctance to eat.
In non-equine species these signs appear similar to foot-and-mouth disease, so testing must be done to make the correct diagnosis. Laboratory testing is the best method to confirm VS, by looking for specific antibodies to the virus in a blood sample or by isolating the virus with a swab sample from a lesion. The virus generally runs its course within two weeks. Typically animals will survive the infection, however, it can take up to two months for the lesions to completely heal.
In order to protect livestock, the following biosecurity measures should be followed:
- Call your veterinarian immediately if you see signs of the disease.
- Separate affected animal(s) from all healthy animals on the property.
- Isolate new or returning animals.
- Handle all healthy animals before sick animals.
- After handling sick animals make sure to wash and disinfect your hands and boots; change and wash clothes as well.
- Control biting flies using fly paper or sugar water.
- Keep animals stalled or under a roof at night to reduce exposure to flies.
- Keep living quarters clean to limit flies.
- Feed and water stock from individual buckets.
- Check exhibitions and other events for veterinary inspection certification requirements, restrictions and their biosecurity policies.
During a 1982 outbreak in an Idaho dairy herd, 320 cows out of a 500-cow herd contracted the disease. The total cost of this outbreak was about $50,000 to the farm (Leder, R. R., Mass, J., & Evermann, J. F., 1983). Outbreaks impact the livestock exhibitions as well. The 2019 Trapper’s Stampede Rodeo at the Cody Stampede Park in Wyoming was postponed due to fears that the participating horses would be exposed to VS. The Ohio Department of Agriculture designated an import restriction for horses from states with confirmed or suspected cases of VS, potentially affecting entrants to the world’s largest single-breed horse show, the All-American Horse Congress scheduled for October 1, 2019, at the Ohio Expo Center.
Check for Movement Restrictions
Vesicular stomatitis can quickly compromise the health of agricultural animals, and adversely impact local and regional economies. In the event of a disease outbreak like this, take extra precautions for your horses and other livestock by practicing the biosecurity measures discussed here, and monitor for signs regularly. States may impose certain restrictions for horses and livestock coming from VS affected states. Click on this link to the Colorado Department of Agriculture website for an example of state restrictions in place during the 2019 VS outbreak. Check with your state animal health officials, or those in the destination state, for information about livestock movement restrictions and other requirements.
Lambert T, Leedom Larson KR. 2016. Vesicular stomatitis virus. Swine Health Information Center and Center for Food Security and Public Health. Retrieved from http://www.cfsph.iastate.edu/pdf/shic-factsheet-vesicular-stomatitis-virus
Traub-Dargatz, J., & Pelzel-McCluskey, A. (n.d.). Overview of Vesicular Stomatitis. Merck Veterinary Manual. Retrieved from https://www.merckvetmanual.com/generalized-conditions/vesicular-stomatitis/overview-of-vesicular-stomatitis
Leder, R. R., Mass, J., & Evermann, J. F. (1983). Epidemiologic investigation of vesicular stomatitis in a dairy and its economic impact. Bovine Practitioner, 18, 45–49. Retrieved from https://www.cabdirect.org/cabdirect/abstract/19842242274
United States Department of Agriculture, Animal and Plant Health Inspection Service (2019, September). 2019 Vesicular Stomatitis Virus (VSV) Situation Report. Retrieved from https://www.aphis.usda.gov/aphis/ourfocus/animalhealth/animal-disease-information/cattle-disease-information/vsv-reports
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