A SOLUBLE PRECIPITATING ANTIGEN (HCA) FROM HOG CHOLERA VIRUS PROPAGATED IN TISSUE CULTURE. II. INCIDENCE OF HCA-ANTIBODIES IN SERA OF HOG CHOLERA-IMMUNE AND NONIMMUNE SWINE.
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Some conditions are presented under which swine develop antibodies for a soluble hog cholera viral antigen (HCA). Precipitating antibodies for HCA were present in all of the immune and hyperimmune anti-hog cholera sera tested. Antibodies for HCA could not be detected in the sera from a large number of swine after vaccination with inactivated hog cholera virus. Many of these same swine did produce HCA-antibodies following challenge with virulent virus. The incidence of these antibodies was significantly higher 3 weeks to one month after challenge than at 10 days. About one-fourth of a smaller group of swine developed HCA-antibodies after vaccination with modified active hog cholera virus vaccine. Exposure to active hog cholera virus appears prerequisite for swine to develop HCA-antibodies. (+info)
HOG CHOLERA. II. RELIABILITY OF THE AGAR DOUBLE DIFFUSION PRECIPITATION TEST FOR THE DIFFERENTIATION OF H.C. VIRUS FROM OTHER INFECTIOUS AGENTS IN SWINE TISSUE.
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The specificity in the agar diffusion precipitation test of the reaction between the antigen of hog cholera virus diffusing from infected tissues and its homologous antibody was verified. Alternate freezing and thawing of infected tissues was found to give optimum release of the antigen from fresh tissue frozen for 18 hours. A study of the effect of the size and age of pigs upon the diffusion of the antigen from tissues showed that tissues from pigs of less than 250 lbs. gave good results provided the tissues were from animals showing gross clinical manifestations. Specimens from infected breeding sows and dead animals usually did not give a reaction. (+info)
HOG CHOLERA. 3. INVESTIGATION OF THE COMPLEMENT-FIXATION TEST FOR THE DETECTION OF THE VIRUS IN SWINE TISSUE.
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The complement-fixation test was investigated as a means of detecting hog cholera virus in spleen from experimentally infected swine. Various methods of extracting the tissue for production of antigen are described and emphasis is placed on the necessity of using the modified direct complement-fixation test to obtain reactions. The tissue should be obtained from animals showing advanced clinical manifestations of the disease. Preferably, the tissue should be maintained frozen or at least well refrigerated. The results indicate that tissue from dead animals or from breeding sows should be avoided. The 77 per cent positive reactions obtained suggest the test could be of diagnostic value provided two or three samples are obtained from the same herd. (+info)
Relation between lymphocyte subpopulations of peripheral blood and immune responses of modified live hog cholera virus vaccine in pigs treated with an ionized alkali mineral complex.
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Thirty-nine healthy pigs (28-32 days old) were purchased from a commercial swine farm and housed at swine pens of the College. The animals were vaccinated intramuscularly (1 ml) with an attenuated live hog cholera virus (HCV, LOM strain) and then boostered at 5 weeks after the first vaccination. The animals were divided into 4 experimental groups: 0.05% (w/w) PowerFeel-supplemented diet (T-1, n = 10); 3% (w/w) SuperFeed-supplemented diet (T-2, n = 10); diluted PowerFeel solution (1 : 500, v/v) as drinking water (T-3, n=9); control (n=10). PowerFeel is an original form of ionized alkali mineral complex (IAMC) and SuperFeed is a commercial product of IAMC. The subpopulation of lymphocyte in blood was assayed by a flow cytometry and HCV-specific antibody was determined by an indirect immunofluorescence assay. In IMAC-treated groups, the proportions of subpopulation expressing MHC-class II, CD2+, CD4+, CD8+, and surface IgM+ B lymphocytes were significantly decreased at 5-weeks after the first vaccination. Significant decreases were also observed in the proportions of MHC-class II, CD2+ and CD8+ lymphocyte at 3-weeks after the booster injection. The humoral immune responses in T-1 and T-2 groups were greater than those in T-3 or control group. These results suggest that IAMC-supplemented diets may have an HCV-specific immunostimulatory effect in pigs. (+info)
Comparison of reverse transcriptase-polymerase chain reaction, virus isolation, and immunoperoxidase assays for detecting pigs infected with low, moderate, and high virulent strains of classical swine fever virus.
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Pigs were experimentally inoculated with Glentorf, Lelystad/97, and Alfort/187: representative low, moderate, and high virulent strains of classical swine fever virus (CSFV). Animals were tested for viremia using virus isolation and reverse transcriptase-polymerase chain reaction (RT-PCR) assays run under routine diagnostic conditions. The virus was detected in the peripheral blood by virus isolation and RT-PCR assays of all Glentorf- and Lelystad/97-infected pigs beginning at 3 days postinoculation (dpi) and in all Alfort/187-infected pigs beginning at 2 dpi. Viremia, as determined by virus isolation, remained detectable in Lelystad/97- and Alfort/187-infected pigs until the last animal within each cohort was euthanized on days 12 and 7 postinoculation, respectively. In contrast, the virus could be isolated from the blood of all Glentorf-infected pigs between 3 and 7 dpi but not from 10 to 21 dpi when the experiment was concluded. Viremia, as determined by RT-PCR, became apparent in Alfort/187-infected pigs at 2 dpi and in Glentorf- and Lelystad/97-infected pigs at 3 dpi. All pigs, regardless of the CSFV strain used, remained RT-PCR positive until they were euthanized. Tonsils were harvested from all the pigs and frozen sections tested for the presence of the CSFV antigen using polyclonal pestivirus and monoclonal CSFV horseradish peroxidase (HRPO) conjugates. Immunostaining reactions were positive for all the Alfort/187- and Lelystad/97-infected pigs. By contrast, tonsils from the Glentorf-infected pigs gave negative to equivocal results. These data suggest that an RT-PCR assay performed on blood may be the best test when dealing with pigs infected with low virulent strains of CSFV. (+info)
An avirulent chimeric Pestivirus with altered cell tropism protects pigs against lethal infection with classical swine fever virus.
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A chimeric Pestivirus was constructed using an infectious cDNA clone of bovine viral diarrhea virus (BVDV) [J. Virol. 70 (1996) 8606]. After deletion of the envelope protein E2-encoding region, the respective sequence of classical swine fever virus (CSFV) strain Alfort 187 was inserted in-frame resulting in plasmid pA/CP7_E2alf. After transfection of in vitro-transcribed CP7_E2alf RNA, autonomous replication of chimeric RNA in bovine and porcine cell cultures was observed. Efficient growth of chimeric CP7_E2alf virus, however, could only be demonstrated on porcine cells, and in contrast to the parental BVDV strain CP7, CP7_E2alf only inefficiently infected and propagated in bovine cells. The virulence, immunogenicity, and "marker vaccine" properties of the generated chimeric CP7_E2alf virus were determined in an animal experiment using 27 pigs. After intramuscular inoculation of 1 x 10(7) TCID(50), CP7_E2alf proved to be completely avirulent, and neither viremia nor virus transmission to contact animals was observed; however, CSFV-specific neutralizing antibodies were detected from day 11 after inoculation. In addition, sera from all animals reacted positive in an E2-specific CSFV-antibody ELISA, but were negative for CSFV-E(RNS)-specific antibodies as determined with a CSFV marker ELISA. After challenge infection with highly virulent CSFV strain Eystrup, pigs immunized with CP7_E2alf were fully protected against clinical signs of CSFV infection, viremia, and shedding of challenge virus, and almost all animals scored positive in a CSFV marker ELISA. From our results, we conclude that chimeric CP7_E2alf may not only serve as a tool for a better understanding of Pestivirus attachment, entry, and assembly, but also represents an innocuous and efficacious modified live CSFV "marker vaccine". (+info)
Comparison of the effects of RNase-negative and wild-type classical swine fever virus on peripheral blood cells of infected pigs.
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Elimination of the RNase activity of classical swine fever virus (CSFV) glycoprotein E(rns) was previously shown to result in virus attenuation. Specific reduction of B cell numbers in the peripheral blood, a typical symptom of CSFV infection in pigs, was not detected on infection with the RNase-negative mutant C-H346Delta [Meyers et al. (1999). J Virol 73, 10224-10235]. The present report shows that this feature is restricted to this specific virus mutant, and does not represent a general property of RNase-negative CSFV. The effects induced by infection with two other RNase-negative and wild-type (wt) CSFV strains on the composition of peripheral blood cells have been further analysed. For all viruses, not only general leukopenia but also a reduction of different subsets of leukocytes (T-lymphocytes, monocytes and granulocytes) was detected. Similar to the results with B-cells, no significant differences with regard to changes in cell number were determined for RNase-negative mutants and wt virus during the initial phase of infection. Later, the values returned to pre-infection levels for the mutants, but stayed at low levels in the wt virus-infected animals. A major difference was reflected in the virus load of the infected animals, which was dramatically higher for pigs infected with wt CSFV, so that reduction of the virus load represents a further marker for attenuation resulting from RNase destruction. Attenuation was also detectable for the RNase-negative mutant C-W300G, which showed rapid reversion to the wt sequence within the infected pig. The prevention of fatal disease after infection with C-W300G is apparently determined during the short time between infection and reversion, as the virus revertant reisolated from infected pigs was shown to be virulent when used for infection in a follow-up study. Reversion of C-W300G was also detected in tissue culture during passage on swine testis epithelioid cells and porcine transformed kidney (MAX) cells, whereas the mutation was stable when SK6 or 38A1D cells were tested. (+info)
Determinants of virulence of classical swine fever virus strain Brescia.
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Two related classical swine fever virus (CSFV) strain Brescia clones were isolated from blood samples from an infected pig. Virus C1.1.1 is a cell-adapted avirulent variant, whereas CoBrB is a virulent variant. Sequence analysis revealed 29 nucleic acid mutations in C1.1.1, resulting in 9 amino acid substitutions compared to the sequence of CoBrB (476)R. Using reverse genetics, parts of the genomes of these viruses, which contain differences that lead to amino acid changes, were exchanged. Animal experiments with chimeric viruses derived from C1.1.1 and CoBrB (476)R showed that a combination of amino acid changes in the structural and nonstructural regions reduced the virulence of CSFV in pigs. Moreover, the presence of a Leu at position 710 in structural envelope protein E2 seemed to be an important factor in the virulence of the virus. Changing the Leu at position 710 in the CoBrB (476)S variant into a His residue did not affect virulence. However, the (710)His in the C1.1.1/CoBrB virus, together with adaptive mutations (276)R, (476)R, and (477)I in E(rns), resulted in reduced virulence in pigs. These results indicated that mutations in E(rns) and E2 alone do not determine virulence in pigs. The results of in vitro experiments suggested that a high affinity for heparan sulfate of C1.1.1 E(rns) may reduce the spread of the C1.1.1/CoBrB virus in pigs and together with the altered surface structure of E2 caused by the (710)L-->H mutation may result in a less efficient infection of specific target cells in pigs. Both these features contributed to the attenuation of the C1.1.1/CoBrB virus in vivo. (+info)