Swine Vesicular Disease - available
Control ToolsDiagnostics availabilityCurrently Prionics is the only Company that commercializes an ELISA kit for detection of antibodies in serum and plasma. Reagents for antigen detection based on ELISA and for antibody detection by competitive ELISA (as described in the OIE manual) are available from the two OIE reference laboratories. Currently Prionics is the only Company that commercializes an ELISA kit for detection of antibodies in serum and plasma. Reagents for antigen detection based on ELISA and for antibody detection by competitive ELISA (as described in the OIE manual) are available from the two OIE reference laboratories. The 5B7-competitive ELISA for antibody detection reported in the OIE manual underwent extensive validation in several EU National Reference laboratories, before being considered as the reference screening test. All assays mentioned at 9.3 section are described in the EC Decision 2000/428 and in the O.I.E. Manual of Diagnostic tests and vaccines for terrestrial Animals. Low, unless surveillance programmes are implemented. Not required as vaccine not authorised or used in Europe. Currently available diagnostic tests are valid tools. In the prospect of herd health status profiling or implementation of serosurveillance programmes for multiple diseases, the development of multiple simultaneous assays on the same sample, including SVDV antibody detection, could be seen as an opportunity. GAPS: Rather than new developments, a modification of recommendations for use of available tests should be considered. For example, extensive experience suggests that for antibody detection ELISA may be more reliable and robust than VNT, so that there is no need to confirm by VNT multiple positive samples detected by ELISA. VNT can remain as reference test only to discriminate the singleton cases. Similarly, RT-PCR proved to be more sensitive and reliable than virus isolation (indicated as the gold standard test). Vaccines availabilityNone. None and not permitted to use vaccines. None. None. Not applicable as no vaccines in use. None. Not applicable at present. No clear market. Barrier protection not applicable by vaccination. Not required based on vaccine availability considerations. Pharmaceutical availabilityNone. None. None. Not applicable. Not required. Not applicable, not required. New developments for diagnostic testsExtended sequencing of isolates would help in selection of best matching primers for application in new RT-PCR assays. 1-2 years for the mentionned requirement (Extended sequencing of isolates). Cost would be affordable; human resources and expertise more demanding. In the prospect of herd health status profiling or implementation of serosurveillance programmes for multiple diseases, the development of multiple simultaneous assays on the same sample, including SVDV antibody detection, could be seen as an opportunity. Extended sequencing of isolates would help in selection of best matching primers for application in new RT-PCR assays.
New developments for vaccinesNot required. Not applicable. High. None at present. New developments for pharmaceuticalsNone. Not applicable. Not applicable. None. Disease detailsDescription and characteristics.Swine Vesicular Disease virus (SVDV) is a member of the genus Enterovirus within the family Picornaviridae, and is a porcine variant of the human pathogen coxsackie B5 virus. The virus has a positive sense single-stranded RNA genome encoding four capsid proteins (VP1, VP2, VP3 and VP4) assembled in a capsid of icosahedral symmetry, and several non-structural proteins. SVDV occurs as a single serotype, in which four congruent groupings were found in both the genetic and antigenic properties of the virus. The most recent group consists of viruses isolated from the European Union since 1992. Isolates of this variant collected in a 20-year period showed a gradual nucleotide substitution rate, while the antigenic profile maintained stable. SVDV is unrelated to other porcine enteroviruses. Phylogenetic studies suggest that it evolved as a genetic sub-lineage of the human pathogen coxsackievirus B5 to which it is antigenically related.
Species involvedSwine (domestic and wild pigs) are the only susceptible species. The carrier state was experimentally shown to be a very rare sequel to infection with SVD virus and is therefore not significant in the epidemiology of the disease. SVD virus has evolved from the human enterovirus coxsackievirus B5 to which it is antigenically related, but transmission of CV-B5 between pigs does not occur. Serconversion or disease was never reported in farmers or veterinarians working with infected pigs; however seroconversion in humans has rarely occurred in laboratory workers associated with mild flu-like clinical disease, with exception of one case of meningitis. None. Pigs are the only species that are naturally infected. No reservoir hosts are known. Description of infection & disease in natural hostsDirect contact with infected pigs or indirect contact via contaminated materials, environment, fomites. Transmission route: oral (main), skin and mucosal lesions. Infectious sources: faeces (major), vesicular fluid, contaminated meat scraps and swill. Airborne transmission of SVDV is insignificant. Not applicable. SVD is characterised by development of vesicles on the coronary band (sometimes resulting in loss of the hoof), interdigital spaces, and occasionally on snout, lips, tongue and teats; shallow erosions may be seen on the knees. Pigs may become temporarily lame and refuse to move even for food. Transient fever up to 41°C may occur. Recovery is usually complete within two to three weeks. The disease may be subclinical, mild or severe, depending on the strain of virus involved, the route and dose of infection, and the husbandry conditions. Morbidity rate in herds may be low but high in pen/contact groups. The main importance of SVD is that it is clinically indistinguishable from foot and mouth disease and other vesicular diseases. However, outbreaks of SVD that have occurred during recent years have been characterised by less severe, or no clinical signs. The incubation period is between 2 and 7 days. Mortality due to SVD is very rare. Affected pigs may excrete virus from the nose and mouth and in the faeces up to 48 hours before the onset of clinical signs. Most virus is produced in the first 7 days after infection, and virus excretion from the nose and mouth normally stops within 2 weeks. Virus may continue to be shed for up to 3 months in the faeces. All tissues contain virus during the viraemic period. SVD virus has a tropism for epithelial tissue (skin and mucosa of digestive tract). Vesicle formation is the only known lesion directly attributable to the infection. Zoonotic potentialVery few human cases have been reported several years ago in laboratory workers with contact with SVDV, but never in farmers or veterinarians working with infected pigs. None Almost none Clinical signs included mild influenza-like symptoms (fever, malaise) with generalized abdominal and muscle pain and weakness. One case developed into aseptic meningitis. All human cases recovered without sequelae. None Impact on animal welfare and biodiversityAt present, SVD has often a sub-clinical course and usually the direct impact of the disease in pigs is quite low. The restriction of animal movement (protection and surveillance zones) may cause sanitary and welfare problems. No. Yes (according to EU legislation). Geographical distribution and spreadSVD was first recorded in Italy in 1966. Later, outbreaks occurred in several European countries and Eastern Asia during the 1970s, early 1980s; then the disease has continued to persist in Italy until the present day and has reappeared in the European Union, outside Italy, on sporadic occasions since 1992. Apart from Italy, where SVD is mostly diagnosed in clinically normal pigs, nowadays the EU is considered free, in most countries uniquely on the basis of absence of clinical evidence. Uncertainty remains on the presence of SVD in some countries in Asia. GAP: due to the prevalent sub-clinical course of the disease, clinical inspection is often ineffective; so that it is necessary to resort to laboratory diagnosis for SVD surveillance. The extent of occurrence of SVD virus outside of Italy is not absolutely clear, since most countries do not undertake the extensive laboratory-backed surveillance needed to be sure of freedom. Apart from very sporadic clinical cases in Europe, SVD is endemic in southern Italy with occasional outbreaks or rarely epidemic waves in central or northern regions, from where it has been rapidly eradicated. No SVD diffusion is mainly related to movement of pigs, means of transport and contaminated material and personnel. High herd density may also play a role in spread between herds. However, SVD may have a limited tendency to spread even within pens of the same farm. GAP: bio-security measures based on principles of direct prophylaxis are not always correctly implemented to prevent incursion of SVD in a farm or in a “new territory”. SVD is a transmissible disease that has the potential for very serious and rapid spread, irrespective of national borders. GAP: increased risk due to subclinical course of disease. No No No No Route of TransmissionDirect contact with infected pigs or indirect contact via contaminated materials, environment, personnel, fomites. Faecal contamination is a major source of virus spread, often within contaminated vehicles. Via contaminated meat scraps and swill. Overcrowding, mixing and transporting animals, transport of pigs in contaminated lorries. Late diagnosis, non clinical infection. GAP: the undisclosed course of SVD may facilitate its diffusion. Detection and Immune response to infectionHumoral response with development of virus neutralizing antibodies is the most important, known mechanism of host reaction to infection. GAP: in the absence of pressure to develop a vaccine, immunological research has not been a priority. Detection of specific antibodies in serum, by ELISA and Virus Neutralisation test, is indicative of present or past infection. On the basis of the typical kinetics of occurrence for the different immunoglobulins, antibody isotyping is useful to ascertain the time of exposure to infection; detection of IgM is indicative of current infection within a pig herd. Main means of prevention, detection and controlEU legislation provides for: stamping out, restriction of pig movements (protection and surveillance zones), cleansing and disinfection, restrictions on swill feeding and on importation of pig products from SVD-affected regions. GAP: in many countries SVD detection is based on clinical evidence. SVD has often a sub-clinical course and when the disease is identified it may have already spread. Stamping out and destruction of affected and in contact pigs, standstill, cleansing and disinfection The diagnosis of SVD requires the facilities of a specialised laboratory. In case of clinical occurrence, differential diagnosis with FMD is essential, and due to the common subclinical course, laboratory investigations are the only mean to scientifically exclude virus circulation. Diagnostic tests for virus detection:
Diagnostic tests for antibodies detection:
GAPS: Available diagnostic tests are valid tools; rather than gaps, a modification of recommendations for use should be considered. For example, extensive experience suggests that for antibody detection ELISA may be more reliable and robust than VNT, so that there is no need to confirm by VNT multiple positive samples detected by ELISA. VNT can remain as reference test only to discriminate the singleton cases. Similarly, RT-PCR proved to be more sensitive and reliable than virus isolation (indicated as the gold standard test). There is currently no commercial vaccine available against SVD. Vaccination is forbidden in EU. Experimental inactivated vaccines against SVDV have been developed but vaccination of pigs has never been undertaken in the field. None Health status certification (holding/animal/product), application of rigorous cleansing and disinfection procedures. GAP: the health status certification (farm/animal) may be proved by appropriate lab investigations Certification on the origin of the animals/product plus health status certification. GAP: certifications are based on the surveillance activities performed, at present there are not harmonized surveillance rules. Health status certification (holding/animal). Application of rigorous cleansing and disinfection procedures. Control on animal movements. Ban on swill feeding. GAP: on the basis of clinical symptoms, it may be difficult to recognize affected animals, also during the acute phase. At present, in many countries surveillance for SVD is based on clinical evidence. Since SVD has often a sub-clinical course, clinical surveillance must be supported by appropriate sampling and laboratory investigations such as serological surveillance and/or detection of SVDV in random sampling of pen-floor faeces. GAP: Surveillance in the EU is based on the assumption that in case SVD enters a susceptible population, clinical symptoms are observed. According to the knowledge acquired on the disease, clinical surveillance has a low sensitivity for detecting virus circulation. A number of European and Far Eastern countries have eradicated SVD in the 70’s, 80’s and 90’s. Since then the only reported cases were in Taiwan (2000), in Portugal (2002, 2004, 2007) and Italy (still present). In case of outbreak, EU legislation provides for a rigorous stamping out policy. GAP: due to the frequent subclinical nature of SVD virus infection and the lack of information on surveillance, the global distribution of the virus cannot be ascertained with certainty. Nowadays the cost of SVD is mainly linked to the control measures applied (stamping out…) and to the stringent control on trade, rather than to the real outcome of the disease in susceptible species (morbidity is very low, mortality is nil). GAP: control measures applied seem disproportionate to the real impact of the disease. Disease information from the OIEYes http://www.oie.int/index.php?id=169&L=0&htmfile=chapitre_1.15.4.htm http://www.oie.int/fileadmin/Home/eng/Health_standards/tahm/2.08.09_SVD.pdf Socio-economic impactNot applicable Not applicable Nowadays the impact of SVD is low, mobility is low and mortality nil. SVD does not cause severe production losses but it is of major economic importance since surveillance, control and eradication measures are costly. Countries which are known to have the disease face embargoes on the export of pigs and by products. Several months of interruption of activity in herds affected by SVD outbreaks. Trade implicationsOutbreaks result in embargo on the export of pigs and pork products. GAP: due to the pathogenesis of SVD, the risk of virus being present in muscle meat is considered to be low (short viraemic period, no replication of virus in the muscles). In case of an SVD outbreak quarantine measures and movements standstill are applied in the affected area. GAP: the control measures foreseen in case of SVD seem disproportionate. In case of an SVD outbreak quarantine measures and movements standstill are applied in the affected area. Main perceived obstacles for effective prevention and controlDifficulties in clinical diagnosis due to the often undisclosed course of the disease, import form countries where the SVD status is not regularly assessed. GAP: the disease was included among the List A for the clinical similarity to FMD. At present SVD is often unapparent. Main perceived facilitators for effective prevention and controlFast and robust diagnostic tools. Surveillance methodologies and appropriate tests to detect unapparent infection. In case SVD occurs clinically, diagnostic tests are available to differentiate SVD and FMD RiskThe risks are associated with the movement of pigs or contaminated materials and transport means from countries where the disease is not diagnosed due either to inadequate surveillance systems or to sub clinical occurrence. ConclusionThe main importance of SVD is that it is clinically indistinguishable from FMD, and any outbreaks of vesicular disease in pigs must be assumed to be FMD until investigated by laboratory tests and proven otherwise. However, subclinical infection has been the most frequent condition observed during recent years. |
