Black flies are always bothersome around livestock animals. This year their presence is even more troublesome because of their transmission of vesicular stomatitis virus (VSV).
“There is compelling evidence that insect vectors, primarily black flies, introduce VSV into populations of domestic animals,” said Jason Turner, New Mexico State University (NMSU) Extension equine specialist. “Last year we had a pretty bad outbreak. Because of the mild winter, and other conditions, black flies are already bothersome and reports of the virus are already being received.”
Outbreaks typically occur in the southwest U.S. beginning in late spring or early summer and normally continue through late fall, progressing northward along riverways and valleys.
“It primarily affects equids, cattle and swine, but it can also occur in sheep, goats, llamas, alpacas and a variety of wild vertebrates,” Turner said. “As a zoonotic disease, VSV can infect humans and cause flu-like symptoms, so it is important that people handling infected horses practice proper biosecurity to protect themselves as well as other animals.”
The incubation period, or time from exposure to presence of clinical symptoms, usually ranges from two to eight days.
“Drooling and excess salivation are typically the first symptoms noticed,” Turner said. “Upon closer examination, there may be blanched areas and the characteristic vesicles or blisters in and around the mouth. These lesions are quite painful and can cause loss of appetite and/or refusal to drink water.”
Minimizing the risk of exposure for horses is the best preventative measure. The following suggestions can help reduce the incidence of vesicular stomatitis:
• Maintain an insect control program;
• Stable horses rather than leaving them on pasture;
• Routinely inspect for signs of VSV and isolate suspected animals from the herd;
• Use individual rather than communal feeders, waterers, bits and tack; and
• Isolate new horses for at least 21 days before turning them with other resident horses.
Because the clinical signs of VSV are indistinguishable from those of foot-and-mouth disease, VSV is a reportable disease, which means veterinarians have a duty to report suspect VSV cases to state and federal animal health authorities. A veterinarian should be called to confirm the diagnosis of VSV through laboratory testing of collected samples.
“If the horse is confirmed positive, then the premises will be quarantined with movement restrictions,” Turner said. “Quarantine periods may range from at least 14 days from the onset of lesions in the last affected animal on the premises to at least 21 days after all lesions are healed.”
Good communication with a veterinarian and animal health official is important in dealing with disease outbreaks such as VSV. — NMSU Extension
