By: Emily Nietrzeba, DVM, MPH
Vesicular stomatitis (VS) is a viral infection that can affect horses, cattle, and pigs, and can also but rarely be seen in goats, sheep, and llamas. Disease manifestation of vesicular stomatitis is blister-like lesions commonly around the tongue, mouth, nose, and lips, but can also present around the coronary bands, udder, or sheath. Vesicular stomatitis is a reportable disease in most states, including California, not only because of rapid transmission but because clinical signs of this disease are identical to those caused by foot and mouth disease in cattle and swine, swine vesicular disease, and vesicular exanthema of swine.
VS transmission occurs via direct contact with sores of infected animals or vector-borne blood transmission. Known vectors for VS transmission include black flies, sand flies, and biting midges (Culicoides spp.), which have been implicated as the likely source of infection in most recent positive premises. Infected animals must be promptly isolated to reduce intra-herd transmission, and positive premises are quarantined for 14 days following the onset of lesions of the last affected animal. Biosecurity measures and vector mitigation efforts are frequently implemented on infected premises to reduce within-herd spread of the virus. No specific treatment for VS is indicated aside from supportive care, usually consisting of pain management and soft feeds in the presence of perioral lesions.
The 2020 VS outbreak began on April 13, 2020, when the National Veterinary Services Laboratories (NVSL) in Ames, Iowa confirmed the first VS-positive premises in Dona Ana County, New Mexico. Arizona, Texas, Kansas, Nebraska, and Oklahoma subsequently broke with VS cases which were confirmed by NVSL on April 22, 2020 (Cochise County, Arizona, April 23, 2020 (Starr County, Texas), June 16, 2020 (Butler County, Kansas), June 24, 2020 (Buffalo County, Nebraska), and July 7, 2020 (Washington County, Oklahoma).
As of July 7, 2020, 122 VS-affected premises have been identified (92 confirmed positive, 30 suspect). One hundred fifteen (115) of these premises had only equine species clinically affected and four premises had clinically affected cattle (McMullen, Starr, and Zapata Counties, Texas). Arizona has identified 19 affected premises (18 confirmed positive, one suspect) in seven counties (Apache, Cochise, Gila, Maricopa, Pima, Pinal, and Santa Cruz Counties). Kansas has identified 74 affected premises (48 confirmed positive, 26 suspect) in seven counties (Butler, Cowley, Greenwood, Marion, Montgomery, Sedgwick, Sumner Counties). Nebraska has identified one affected premises in one county (Buffalo County). New Mexico has identified 16 affected premises (13 confirmed positive, three suspect) in six counties (Bernalillo, De Baca, Dona Ana, Eddy, Grant and Sierra Counties). Oklahoma has identified one affected premises (one confirmed positive) in one county (Washington County). Texas has identified 10 affected premises (10 confirmed positive, 0 suspect) in six counties (El Paso, Hudspeth, Kerr, McMullen, Starr, and Zapata Counties).
There have been a total of 68 previously VS-infected or suspect premises that have completed the quarantine period and been released. The last VS-quarantined premises was released in New Mexico on June 4, 2020 and in Texas on June 8, 2020. Fifty-four (54) premises remain under VS quarantine in Arizona, Kansas, Nebraska, and Oklahoma.
Both VS-Indiana (VS-IN) and VS-New Jersey (VS-NJ) serotypes have been identified during the 2020 outbreak. VS-IN occurred in the U.S. in 2019, while VS-NJ was last isolated in the U.S. in the 2014-2015 outbreak. Both serotypes are known to circulate in endemic cycles in southern Mexico. The last U.S. outbreak involving both serotypes occurred in 1997-1998.
For import into California, all horses, cattle, sheep, goat and swine originating from any state where vesicular stomatitis has been diagnosed (except cattle and swine transported directly to slaughter) must be accompanied by a health certificate (Certificate of Veterinary Inspection) signed by an accredited veterinarian that includes the following statement:
“I have examined all the animals identified on this certificate within 7 days of shipment date and found them to be free from signs of Vesicular Stomatitis (VS). During the last fourteen (14) days, these animals have not been exposed to VS nor located on a VS confirmed or a VS suspected premises.”
