Swine vesicular disease is a viral vesicular disease of pigs caused by an enterovirus closely related to human coxsackie virus B5. It is generally a mild disease that was endemic in Italy until recently; it has occurred only sporadically in other countries. Its importance is as a differential diagnosis for foot-and-mouth disease, from which it is clinically indistinguishable.
Swine vesicular disease (SVD) is typically a transient disease of pigs in which vesicular lesions appear on the feet and snout and in the mouth. SVD is usually mild in nature and may infect pigs subclinically. However, the disease is of major economic importance, because it must be differentiated from foot-and-mouth disease (FMD), eradication is costly, and embargoes on export of pigs and pork products are often imposed on nations not free of SVD.
Pigs are considered the only natural host of the virus, although it can infect sheep in close contact with infected pigs. SVD has been reported only in Europe and Asia, having been first identified in Italy in 1966 and subsequently in Hong Kong, Japan, Taiwan, and 16 other countries in Europe. Although SVD virus was eradicated from Japan in the mid-1970s and most European countries by the mid-1980s, it had remained endemic in Italy and caused sporadic outbreaks of disease in other European countries during the 1990s and in Portugal in 2003, 2004, and 2007. As of 2020 it was reported to be eradicated from the Italian pig industry.1
References
Tamba M, Plasmati F, Brocchi E, and Ruocco L. Eradication of Swine Vesicular Disease in Italy. Viruses. 2020;12(11):1269. doi:10.3390/v12111269
Etiology of Swine Vesicular Disease
The causal agent of SVD is an enterovirus of the family Picornaviridae. It belongs to the species human enterovirus B and is thought to have evolved from the human pathogen coxsackievirus B5, with which it shares a close antigenic and genetic relationship. There is only one serotype of SVD virus, although isolates may be differentiated by antigenic or genetic typing and may differ in virulence. SVD virus is transmitted by direct or indirect contact or by ingestion of infected pork or pork products. Infection is via the oral route or through skin abrasions, and can cause viremia, fecal viral shedding, and generalized vesicles that rupture to release large amounts of virus.
Clinical Findings and Lesions of Swine Vesicular Disease
The primary clinical signs of SVD are fresh or healing vesicular lesions on the feet, especially the coronary band, and less often other areas such as the mouth, lips, teats, or snout. The lesions may be mild or inapparent, especially when pigs are kept on soft bedding. The lesions are similar to those of FMD, vesicular exanthema of swine, Seneca Valley virus, and vesicular stomatitis; however, affected pigs usually do not lose condition, and the lesions heal rapidly. Nervous system signs have been described but are rarely observed in the field. The World Organization for Animal Health recommends that any outbreaks of vesicular disease in pigs should be assumed to be FMD until proved otherwise by means of laboratory testing.
Diagnosis of Swine Vesicular Disease
Laboratory testing of samples of epithelium, feces, or serum
Virus isolation
Serologic testing
Diagnosis of SVD is confirmed by laboratory testing of samples of epithelium, feces, or serum from affected animals. Virus detection is via antigen-detection ELISA, virus isolation, or reverse-transcriptase PCR assay. Serologic diagnosis is by means of antibody-detection ELISA or virus neutralization test; however, low specificity may be a concern, particularly in older animals. In clinical cases, the preferred specimens are lesion material collected in phosphate-buffered saline. Subclinical infection may be detected by testing of pen-floor feces samples using reverse-transcriptase PCR assay or virus isolation. SVD is not longer a listed disease with the World Organization for Animal Health because of its mild clinical signs and ease of differentiation from FMD by means of laboratory testing. However, it remains a notifiable disease in some countries.
Control of Swine Vesicular Disease
Controlling the import of pigs and pork products
Appropriate methods of treating pork products to kill the virus
Banning or regulating feeding of garbage to pigs
Countries free of SVD can remain so by controlling the import of pigs and pork products or by ensuring that pork products are treated (heat or otherwise) to kill the virus. Feeding of garbage to pigs may be banned or regulated to ensure thorough cooking of raw animal products. Any suspected outbreak should be reported to the appropriate authorities as required. If SVD does occur, control is by biosecurity measures, including restrictions on pig movement. There are no commercially available vaccines. Extensive serosurveillance is necessary to detect subclinically infected herds, and seroreactor herds must be followed up by clinical inspection and fecal virus testing. The virus is extremely resistant in the environment and is stable over a wide pH range (2.5–12); thus, disinfection of premises, trucks, and equipment must be thorough. The most effective disinfectants are strong alkalis, although hypochlorites or acid-containing iodophors can be used when organic material is not present.
Key Points
SVD is a mild, viral disease that causes vesicular lesions and is indistinguishable from FMD.
The virus that causes SVD is extremely resistant and can survive for months in the environment and in meat products.
For More Information
OIE Technical Disease Card: Swine Vesicular Disease
