3 minute read
Vesicular Stomatitis Virus: The Dreaded ‘Look-alike’
By Emily Nietrzeba, DVM, MPH, CDFA Animal Health Branch Veterinarian Specialist
Unusual weather and precipitation patterns bring additional challenges to California’s human and animal residents, including early or sudden appearance of diseasecarrying insect vectors like biting flies and mosquitoes. The recent heavy rains in California and other areas of the southwest have hastened the northward migration of the Simuliidae black flies that can carry the virus which causes vesicular stomatitis (VSV).
Most animal health officials take a deep breath and count to ten at the mention of “vesicles” of any sort, but the appearance of any such lesions should also be immediate cause for action from veterinarians and livestock producers. Vesicular stomatitis is an emergency condition in California and nationally, reportable within 24 hours of suspicion or detection because the lesions it causes in cloven-hooved livestock are visually indistinguishable from those caused by the devastating Foot and Mouth Disease virus (FMDV). Horses are not susceptible to FMDV, but the possibility of VSV viral transmission from equids to livestock species and the inability to distinguish VSV and FMDV lesions without comprehensive testing causes any confirmed VSV detection in any species to trigger a state and federal coordinated disease mitigation response. Vesicular lesions in any large animal species should be immediately reported to the California Department of Food and Agriculture (CDFA) or the U.S. Department of Agriculture (USDA). Animal health officials and regulatory veterinarians specifically trained as
Foreign Animal Disease Diagnosticians (FADDs) can assist with correct sample submission for accurate and timely diagnostics, implementation of disease control measures like prompt isolation and enhanced biosecurity measures, and usage of appropriate personal protective equipment (PPE) and disinfectants.
VSV is highly contagious and primarily affects equids and cattle, but it can also affect camelids, small ruminants, and occasionally swine. While rarely fatal, clinical signs frequently include hypersalivation and decreased appetite caused by the presence of painful blister-like lesions (vesicles) commonly around the mouth, tongue, oral cavity, and sometimes around the nares, teats, genitals, and coronary bands. Vesicles are caused by the biting fly vector depositing VSV directly into these sensitive tissues, and the lesions can be highly contagious by direct contact for up to seven days following rupture of the vesicles. The enveloped RNA virus is rapidly inactivated by UV exposure like sunlight but can survive in water for a limited period of time; therefore, communal water troughs and waterers can be sources of ongoing indirect transmission. VSV is also potentially zoonotic, so appropriate PPE and safe sampling techniques should always be utilized when VSV is suspected. While self-limiting, VSV can cause fever, malaise, body aches, and other flu-like symptoms in humans.
The confirmation of VSV in any state triggers interstate and international movement restrictions because it is an FMDV “look-alike.” Mandatory quarantines on affected premises are in effect for a minimum of fourteen (14) days following the appearance of the last clinical lesions, but the majority of states impose additional restrictions on susceptible species originating from VSV-affected states and/or counties. Additional entry requirements for susceptible species originating from an affected state usually include a shortened inspection and validity period for a certificate of veterinary inspection (CVI), as well as a certification statement by the issuing veterinarian that the animal(s) have not been on a VSVaffected premises within a specified period of time and are free of any clinical signs of disease. International shipments usually require additional negative confirmatory testing. Exposed animals can have a VSV-positive antibody titer for up to twelve (12) years following exposure to the virus. While seropositive animals are no longer contagious after the resolution of lesions, this serological evidence needs to be taken into account, as it may impede future international travel.
Treatment of VSV is primarily supportive, involving pain and nutrition management and judicious treatment of secondary bacterial infections. No effective vaccine is currently available, but insect vector control and rapid isolation of clinical cases are critical measures of VSV mitigation. Veterinarians should routinely communicate with their large animal clients and producers regarding fly and mosquito control measures, especially during periods of insect migration and heavy burdens.
CDFA and USDA are ready and willing to provide direction on effective vector-control measures and biosecurity recommendations to ensure that California veterinarians are prepared to protect their patients and support their clients.
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