Vesicular Stomatitis 2020 Updates

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.”

West Nile Virus 2020 Updates

By: Emily Nietrzeba, DVM, MPH

The first 2020 case of equine West Nile Virus (WNV) in California has been confirmed in Amador County. A 20-year-old Quarter Horse gelding displaying acute severe neurological signs with unknown vaccination history was confirmed positive for WNV on June 26, 2020. The gelding is currently alive.

West Nile Virus is the leading cause of arthropod-borne encephalitis (brain inflammation) in horses and humans in the United States, with horses representing 96.9% of all non-human mammalian cases. The virus is present in all 48 continental states, Mexico, and Canada, and is transmitted from avian reservoir hosts to mammals by a variety of mosquito species.

It is important to remember that both humans and horses are considered dead-end hosts for WNV and the virus is not directly contagious from horse to horse or horse to human. WNV vaccination is considered a core vaccination by the American Association of Equine Practitioners and an essential standard of care for all horses in North America. 

This is an excellent opportunity to remind friends and colleagues of the importance of developing and adhering to a protective vaccination program with their veterinarian, and to discuss vector control measures at home and on farm. In addition to minimizing equine (and human) exposure to mosquitos during peak feeding periods of dawn and dusk and appropriate application of mosquito repellant, effective mosquito abatement recommendations include:

• Draining unnecessary standing water found in wheelbarrows, tires, etc.

• Cleaning water containers at least weekly (i.e., bird baths, plant saucers)

• Scheduling pasture irrigation to minimize standing water

• Keeping swimming pools optimally chlorinated and draining water from pool covers

• Stocking of water tanks with fish that consume mosquito larvae (Contact local mosquito control for assistance) or use mosquito “dunk” available at hardware stores

First 2020 Case of Equine West Nile Virus in California

The first 2020 case of equine West Nile Virus in California has been confirmed in Amador County.  A 20-year-old Quarter Horse gelding displaying acute severe neurological signs with unknown vaccination history was confirmed positive for WNV on June 26, 2020. The gelding is currently alive.

Please contact your veterinarian to set up a protective vaccination program, and to discuss vector control measures on your ranch/farm.

Vesicular Stomatitis has been confirmed in New Mexico

Below are the case details and new entry requirements for horses, cattle, sheep, goat and swine entering California from a VS Affected State.

Additional information can be found at https://wwwcdfa.ca.gov/ahfss/Animal_Health/VS.html .

Situation Update:

On April 13, 2020, the National Veterinary Services Laboratories (NVSL) in Ames, Iowa, confirmed a finding of vesicular stomatitis virus (VSV) infection (Indiana serotype) on an equine premises in Dona Ana County, New Mexico.  VSV-Indiana serotype was last isolated in the U.S. during the 2019 VSV outbreak. A single horse on the index premises has met the case definition of infection with compatible clinical signs and virus isolation positive results.  A second equine premises in Sierra County, New Mexico subsequently met confirmed VSV case definition with compatible clinical signs and reverse transcription-polymerase chain reaction (RT-PCR)-positive results for VSV (Indiana serotype). This is the 2020 VSV index case for the United States and subsequent VSV case for New Mexico. 

Index and Subsequent Confirmed Positive Premises:  Both premises are small equine properties, one located in Dona Ana County and the other located in Sierra County, New Mexico and are currently under state quarantine.  The index premises in Dona Ana County has only one horse on the property and the horse presented with coronary band lesions around April 6, 2020.  There are no other animals on the premises and there have been no livestock movements on or off the premises.  The second VSV-infected premises is located in Sierra County, New Mexico, and has a total of 3 horses with only 1 horse showing coronary band lesions which were first noted around April 8, 2020.  There are no other susceptible species on the premises and there have been no livestock movements onto the premises.  

Known competent vectors for transmission of VSV include black flies, sand flies, and biting midges (Culicoides spp.).  The epidemiological investigations on both VSV-positive premises indicate that incursion of VSV-infected insect vectors is the likely source of infection in these herds.   Biosecurity measures and vector mitigation have been instituted to reduce spread of the virus.  The animals are being monitored and the VSV-positive premises will remain under state quarantine until 14 days from the onset of lesions in the last affected animal on the premises. 

Vesicular Stomatitis Requirements for Importing Horses, Cattle, Sheep, Goats and Swine into California:

All horses, cattle, sheep, goat and swine *originating from any state where vesicular stomatitis (VS) has been diagnosed (except cattle and swine transported directly to slaughter) must be accompanied by a health certificate (certificate of veterinary inspection) and signed by an accredited veterinarian that includes the following statement:

“I have examined all the animals identified on this certificate within 72 hours of shipment date and found them to be free from signs of Vesicular Stomatitis (VS). During the last thirty (30) days, these animals have not been exposed to VS nor located on a VS confirmed or a VS suspected premises.”

*For purposes of this requirement, “originating” means horses, cattle, sheep, goats, and swine that initially leave the VS infected state and come to California, or those that leave any state, visit an infected state, and then return to California.

The California Horse Racing Board (CHRB) has no additional requirements, at this time, on horses coming from a VS-infected area to enter race tracks and/or CHRB-approved training centers. For more information, contact CHRB at 916-263-6000.

Please contact your veterinarian if you have questions or concerns.

Equine Herpesvirus-1

April 9, 2020: A 10-year-old Warmblood mare displaying neurologic signs has
been confirmed positive for Equine Herpesvirus-1. The mare is quarantined and isolated at a referral hospital where she is receiving care.  The Sonoma County home premises containing 48 horses is quarantined with enhanced biosecurity measures and twice daily temperature monitoring of all horse. CDFA will continue to oversee the situation. There is no link between this premises and the current EHV-1 quarantine premises in Alameda county.