JAVMA, Vol 216, No. 9, May 1, 2000 Vet Med Today: Public Veterinary Medicine 1399 Public Veterinary Medicine: Regulatory Medicine V esicular stomatitis (VS) is a viral disease that affects several livestock species, including horses, cattle, and swine. 1-3 The causative virus is in the Vesiculovirus genus of the Rhabdoviridae family. Two serotypes of vesicular stomatitis virus (VSV) are responsible for disease in the United States and are named for the state in which each was initially isolat- ed: VSV Indiana (VSV-IN) and VSV New Jersey (VSV- NJ). 2 Historically, VS has occurred sporadically in the western United States. 3-5 Recently, outbreaks have been detected with increasing frequency; 3 outbreaks (in 1995, 1997, and 1998) have been identified in the past 4 years. This apparent increase in VS occurrence has been of concern because of strict regulatory measures for this disease and their substantial economic impact on the livestock industry. 3-5 The Office Internationale des Epizooties has clas- sified VS as a List A disease, which is defined as a com- municable disease that has the potential to spread rapidly, is of serious socioeconomic or public health consequence, and is of major importance in the inter- national trade of livestock or livestock products. 6 When VS is officially diagnosed in an animal in the United States, the affected premises are designated as positive premises and quarantined until 30 days after resolution of clinical signs in any affected animal. Further, movement of livestock between states may be restricted or banned during outbreaks, and interna- tional trade of US livestock and products is affected. 3,4 The apparent increase in VS has been accompanied by recent reports of erosive stomatitis of unknown ori- gin in horses. 7,8 However, it is unclear whether these reports represent an actual increase in this type of dis- ease or increased awareness attributable to recent VS outbreaks. The purpose of the study reported here was to report clinical and serologic findings in horses with clinical signs that were consistent with VS but were apparently not associated with VSV infection. Materials and Methods Outbreak and case definition—The 1998 VS outbreak began in May with the first cases identified in New Mexico. 9 By July 1998, animals with positive test results for VS were identified in northern Colorado, and many premises were Oral vesicular lesions in horses without evidence of vesicular stomatitis virus infection From the Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523 (Kim, Morley, Mumford, Salman); USDA:Animal and Plant Health Inspection Service:Veterinary Services:Centers for Epidemiology and Animal Health, Fort Collins, CO 80524 (McCluskey); and USDA:Animal and Plant Health Inspection Service:National Veterinary Services Laboratories, Ames, IA 50010 (Swenson). Supported by the Colorado State University College of Veterinary Medicine and Biomedical Sciences College Research Council, the Morris Animal Foundation, and a grant from the USDA Foreign Agriculture Service. The authors thank Drs. W. Cunningham and J. Collins, and R. Forde, D. Fincham, B. Kesl, and K. Wayland for technical assistance. Address correspondence to Dr. Morley. Lisa’Marie Kim, DVM; Paul S. Morley, DVM, PhD, DACVIM; Brian J. McCluskey, DVM, MS, DACVPM; Elizabeth L. Mumford, DVM, MS; Sabrina L. Swenson, DVM, PhD; M. D. Salman, DVM, PhD, DACVPM Objective—To report clinical and serologic findings in horses with oral vesicular lesions that were consis- tent with vesicular stomatitis (VS) but apparently were not associated with VS virus (VSV) infection. Design—Serial case study. Animals—8 horses. Procedure—Horses were quarantined after appear- ance of oral lesions typical of VS. Severity of clinical signs was scored every 2 to 5 days for 3 months. Serum samples were tested for antibodies by use of competitive ELISA (cELISA), capture ELISA for IgM, serum neutralization, and complement fixation (CF). Virus isolation was attempted from swab specimens of active lesions. Results—2 horses with oral vesicular lesions on day 1 had antibodies (cELISA and CF) against VSV; how- ever, results of CF were negative by day 19. Five of the 6 remaining horses were seronegative but devel- oped oral lesions by day 23. Virus isolation was unsuc- cessful for all horses. Conclusions and Clinical Relevance—Horses were quarantined for 75 days in compliance with state and federal regulations. However, evidence suggests that oral lesions were apparently not associated with VSV infection. The occurrence in livestock of a vesicular disease that is not caused by VSV could confound efforts to improve control of VS in the United States and could impact foreign trade.Vesicular stomatitis is of substantial economic and regulatory concern. (J Am Vet Med Assoc 2000;216:1399–1404)