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Encephalomyocarditis virus was isolated from the organs of swine dying during an outbreak of an acutely fatal disease occurring on a farm in Panama. The outstanding lesion was severe myocarditis. Pigs inoculated with the viral isolate developed a systemic infection with myocarditis.
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With regard to the legal regulations for the diagnosis of Aujeszky's disease in pigs, a retrospective immunoenzymatic study was performed on brains of 20 pigs, in which Aujeszky's disease had been diagnosed based only on clinical, macroscopical and histological findings, although the etiological agent could not be demonstrated neither by immunofluorescent technique nor by virological cultivation. Applying the peroxidase-antiperoxidase-(PAP) method, in 6 of 20 animals (30%) viral antigen of porcine herpesvirus type 1 was demonstrated in situ in at least two of five different locations of the brain. Reasons for negative results in immunohistological and virological investigations are discussed and the significance of the performed immunoenzymatic technique is pointed out.
We studied VP0 cleavage of Swine vesicular disease virus (SVDV), a member of the Picornaviridae using a full-length cDNA copy of the Dutch SVDV isolate. The influences of mutations, introduced at the cleavage site of SVDV, on VP0 cleavage, RNA encapsidation and viral infection were studied. Double mutations at asparagine (VP0 aa 69) and serine (VP0 aa 70) resulted in no cleavage of VP0 and 100% inhibition of virus production. Mutation of the asparagine into threonine or phenylalanine resulted in a low amount of cleaved VP0 and infectious virus was found. After passage of this mutated virus VP0 cleavage became more efficient and the growth rate of the virus became similar to wild-type SVDV. The passaged virus had mutated at the asparagine site; the threonine had changed into an alanine and the phenylalanine into a cysteine. When the serine was mutated no maturation cleavage was observed and no infectious virus could be derived. All the mutations resulted in RNA encapsidation. We conclude that in the case of SVDV the cleavage site between VP2 and VP4 is essential for the formation of infectious virus which is comparable to poliovirus. The serine of the VP0 site was more important than the asparagine in this respect.
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Following the first serum survey for swine vesicular disease [SVD] in Great Britain in 1974 (Watson and Hedger 1974), three further surveys have been carried out. In these four surveys an overall total of 9760 sera have been examined, involving pigs from 958 premises in the first three surveys and an unknown number of premises in the fourth survey taken on a national basis. Forty-three farms were visited as sources of origin or possible sources of origin of the pigs from which positive or inconclusive results were obtained. Subsequent to the one clinical case of disease already reported with the results of the first survey, no further clinical cases of SVD have been confirmed, although lesions suggestive of the disease were found in some pigs on four of the premises visited. SVD quarantine restrictions on these four farms were removed subsequent to further serological sampling and when there was no indication that a spreading vesicular condition existed.
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Two methods were evaluated for the inactivation of African swine fever (ASV) and swine vesicular disease (SVD) viruses in pig slurry: chemical treatment and heat treatment. The addition of NaOH or Ca(OH)2 at different concentration/time combinations at 4 degrees C and 22 degrees C was examined, as was virus stability at different temperature/time combinations. ASF virus (ASFV) was less resistant to both methods than SVD virus (SVDV). In slurry from one source, ASFV was inactivated at 65 degrees C within 1 min, whereas SVDV required at least 2 min at 65 degrees C. However, it was found that thermal inactivation depended on the characteristics of the slurry used. Addition of 1% (w/v) of NaOH or Ca(OH)2 caused the inactivation of ASFV within 150 s at 4 degrees C; 0.5% (w/v) NaOH or Ca(OH)2 required 30 min for inactivation. NaOH or Ca(OH)2 (1% (w/v)) was not effective against SVDV at 22 degrees C after 30 min, and 1.5% (w/v) NaOH or Ca(OH)2 caused inactivation of SVDV at both 4 degrees C and 22 degrees C. At higher chemical concentrations or temperatures, ASFV and SVDV inactivation was faster in slurry than in buffered medium.
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Morphological alterations of IB-RS-2 cells cultured in serum-free maintenance medium after inoculation of swine vesicular disease virus (SVDV) were studied electron-microscopically. Cells harvested 0 to 3 hours after inoculation showed no alterations. Cellular alterations were observed from 4 to 7 hours after inoculation. Many vacuoles appeared just beneath the cytoplasmic membrane and were separated by thin cytoplasm. Narrow pathways were sometimes seen in the degenerative cells. They occasionally ran from the vacuole just beneath the cytoplasmic membrane to the nuclear cistern. Ribosome-like granules were seen along the narrow pathway or diffusely in the cytoplasm, or accumulated to form an islet. Membrane-bound bodies were frequently noticed in the central region of the cell. Cytoplasmic blebs were sometimes seen projecting from the cell surface. Vacuoles, narrow pathways and cytoplasmic blebs were absent in cells cultured in the medium with serum. So serum might exert some effects on the cytoplasmic membrane or cytoskeletal framework. Crystalline arrays of SVDV were found in the cytoplasm of degenerative cells harvested from 4 to 7 hours after inoculation. They were near the ribosome-like granules and membrane-bound bodies, but had no relationship with vacuoles just beneath the cytoplasmic membrane and narrow pathway. Their size and morphology were the same as those seen in the cells cultured in the medium with serum.
An indirect ELISA incorporating a protein A-peroxidase conjugate was developed for detecting antibodies to swine vesicular disease virus (SVDV) in pig sera. This test and a conventional virus neutralization test were found to be equally sensitive. A total of 2846 pig sera collected from various abattoirs in South Africa were tested using the indirect ELISA. No serological evidence of infection with SVDV in pigs in South Africa was found.