On August 17, 2006, the National Veterinary Services Laboratories (NVSL) in Ames, Iowa confirmed vesicular stomatitis in a 10 year old horse on a premises in Natrona County, Wyoming (this is near Casper). This is the first confirmed case of vesicular stomatitis (VS) in the United States in 2006; the last case of VS was confirmed in late 2005.
VS is a viral disease which primarily affects horses, cattle, and swine. The viruses that cause VS have a wide host range. VS also occasionally affects sheep and goats. In affected livestock, VS causes blisterlike lesions to form in the mouth and on the dental pad, tongue, lips, nostrils, hooves, and teats. These blisters swell and break, leaving raw tissue that is so painful that infected animals generally refuse to eat and drink, and show signs of lameness. Weight loss usually follows, and in dairy cows, a drop in milk production commonly occurs. Affected livestock may appear to be clinically normal and continue to eat, but may consume only about half of their normal quantity of feed.
The clinically ill horse was positive for antibodies to vesicular stomatitis New Jersey (VS-NJ) virus on the competitive enzyme-linked immunosorbent assay (cELISA) and was also positive on virus isolation for VS-NJ virus. The VS compatible clinical signs and presence of VS-NJ virus meet the definition to classify this horse as the index case for the Nation in 2006. There are an additional 29 clinically normal horses and 25 clinically normal cattle also on the premises.
The affected horse was initially examined as part of a routine physical exam by a private veterinary practitioner on August 12, 2006. The next day, the owner of the horse noticed that the horse had a swollen muzzle and contacted the veterinarian who came back to the premises to re-examine the animal on August 14. During the re-examination, the practitioner noticed that the horse had oral lesions that were consistent with a vesicular condition and immediately contacted APHIS, Veterinary Services in Wyoming. A foreign animal disease investigation was initiated that same day; appropriate samples were collected and submitted to NVSL. There is no history of recent movement of this horse from the premises, however, the owners did report a large burden of Culicoides and large numbers of biting flies in the vicinity.
The affected premises is currently under State quarantine. Additional control measures include isolating the horse from the rest of the animals to ensure that water troughs and feed buckets are not being shared with other susceptible animals, and increasing insect control measures.
The Wyoming Department of Agriculture is beginning a public and veterinary practitioner information and education campaign regarding VS.
APHIS Veterinary Services and the Wyoming Department of Agriculture will continue to monitor the situation and conduct response activities in an ffort to minimize trade restrictions.