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PubMed2004

Does multiple oral vaccination of wild boar against classical swine fever (CSF) have a positive influence on the immunity?

We studied the efficacy of multiple vaccinations of wild boar against classical swine fever (CSF) using a C-strain vaccine. The study consisted of two experiments. In the first experiment, 7 to 8 months old animals were vaccinated either three or four times at an interval of 7 days or twice at an interval of 14 or 28 days. In the second experiment, the efficacy of oral immunisation in young boars (3 months old) was examined after fivefold vaccination at intervals of 14 or 28 days. Independently of the immunisation scheme all wild boar developed neutralising antibodies. An evaluation of the antibody titres 28 days after the initial vaccine application showed that single vaccination and triple immunisation at an interval of 7 days induced the highest antibody titres (X > or = 1/80). In multiple vaccinated young boars (vaccinated at intervals of 14 or 28 days) the third vaccination led to a slight reduction or to an only moderate increase of the antibody titre. In a challenge study after the fifth vaccination all wild boar were protected (no viraemia, no virus excretion, no post-mortem virus detection in organs). This was confirmed by the fact that sentinel animals were not affected. Although other immunisation schemes also were effective, booster vaccination at an interval of 28 days is recommended as basic procedure for eradication of CSF in wild boar. Triple vaccination might also be used at the beginning of the control measures.

Administration, Oral↗
PubMed1998

An experimental infection with classical swine fever virus in weaner pigs. I. Transmission of the virus, course of the disease, and antibody response.

The spread of Classical Swine Fever (CSF) virus (strain Lorraine), originally isolated in the first CSF infected herd of the 1993-1994 Belgian epizootic, was examined in an isolation unit with three adjacent pens and 15 weaner pigs per pen. Virus was introduced through experimental inoculation of one weaner pig in the middle pen (pen 2). The experimentally inoculated pig became viraemic 4 days post-inoculation (dpi) and the pen mates at 12 (n = 9) and 14 dpi (n = 5). The first viraemia in pens 1 and 3 was observed 18 dpi. Pigs were found to be seropositive in pens 1, 2, and 3 from 24, 20, and 22 dpi onwards, respectively. The reproduction ratio (R0) for the pigs in pen 2, estimated according to the martingale method, was 81.3 (s.e. = 109.54). The rate ratio (Cox proportional hazard) of the first pigs to become viraemic in pen 3 (airborne contact plus contact via contaminated clothing and footwear with pen 2) versus pen 1 (airborne contact with pen 2 only) was 1.60 (P = 0.3342). Thus, the additional contact of contaminated clothing did not affect transmission of the CSF virus. The survivor function (Kaplan-Meier survival analysis) did not significantly differ per pen. The time from first detection of virus in plasma to death was not significantly different between pens. The mean rectal temperature of pigs in a pen increased 3 to 4 days prior to detection of virus. The proportion of seropositive pigs per pen (p) from the day the first weaner pig in a pen became viraemic (dpf) was examined as a function of time with a logistic regression model. The model parameter estimates did not differ between pens. Hence, the data from the three pens were pooled. The regression equation of the seroprevalence over time for the pooled data was p = 1/[1+e(4.65-0.39 *dpf)].

Animal Husbandry↗
PubMed1999

Transmission of classical swine fever virus within herds during the 1997-1998 epidemic in The Netherlands.

In this paper, we describe the transmission of Classical Swine Fever virus (CSF virus) within herds during the 1997-1998 epidemic in The Netherlands. In seven herds where the infection started among individually housed breeding stock, all breeding pigs had been tested for antibodies to CSF virus shortly before depopulation. Based upon these data, the transmission of CSF virus between pigs was described as exponential growth in time with a parameter r, that was estimated at 0.108 (95% confidence interval (95% CI) 0.060-0.156). The accompanying per-generation transmission (expressed as the basic reproduction ratio, R0) was estimated at 2.9. Based upon this characterisation, a calculation method was derived with which serological findings at depopulation can be used to calculate the period in which the virus was with a certain probability introduced into that breeding stock. This model was used to estimate the period when the virus had been introduced into 34 herds where the infection started in the breeding section. Of these herds, only a single contact with a herd previously infected had been traced. However, in contrast with the seven previously mentioned herds, only a sample of the breeding pigs had been tested before depopulation (as was the common procedure during the epidemic). The observed number of days between the single contact with an infected herd and the day of sampling of these 34 herds fitted well in the model. Thus, we concluded that the model and transmission parameter was in agreement with the transmission between breeding pigs in these herds. Because of the limited sample size and because it was usually unknown in which specific pen the infection started, we were unable to estimate transmission parameters for weaned piglets and finishing pigs from the data collected during the epidemic. However, from the results of controlled experiments in which R0 was estimated as 81 between weaned piglets and 14 between heavy finishing pigs (Laevens et al., 1998a. Vet. Quart. 20, 41-45; Laevens et al., 1999. Ph.D. Thesis), we constructed a simple model to describe the transmission of CSF virus in compartments (rooms) housing finishing pigs and weaned piglets. From the number of pens per compartment, the number of pigs per pen, the numbers of pigs tested for antibodies to CSF virus and the distribution of the seropositive pigs in the compartment, this model gives again a period in which the virus most probably entered the herd. Using the findings in 41 herds where the infection started in the section of the finishers or weaned piglets of the age of 8 weeks or older, and of which only a single contact with a herd previously infected was known, there was no reason to reject the model. Thus, we concluded that the transmission between weaned piglets and finishing pigs during the epidemic was not significantly different from the transmission observed in the experiments.

Animals↗
PubMed2005

Validation of a real-time RT-PCR assay for sensitive and specific detection of classical swine fever.

A fully validated, ready-to-use, real-time reverse transcription-polymerase chain reaction (RT-PCR) assay, multiplexed for simultaneous detection of an internal control, for the simple and rapid diagnosis of classical swine fever (CSF) was developed. Primers and FAM-labeled TaqMan-probes specific for classical swine fever virus (CSFV) were selected from the consensus sequence of the 5' non-translated region (5' NTR) of 78 different CSFV strains. For determining analytical sensitivity, an in vitro transcript (T7-PC3alf) of the 5' NTR was constructed and tested. In addition, the T7-PC3alf transcript was further used as a positive control and a standard for quantitation of CSFV genome copies. A second heterologous in vitro transcript based on a specific primer-probe HEX-system was designed as an internal positive control for the RNA isolation step and RT-PCR. By using limited primer concentrations for the internal control, no adverse effects on the sensitivity of the CSF-system could be observed, and the newly designed duplex real-time RT-PCR proved to have a sensitivity of approximately eight copies. The primer-probe combination selected was strictly CSFV-specific and no amplification was observed in all non-CSFV pestiviruses tested.

5' Untranslated Regions↗
PubMed2006

In planta production of two peptides of the Classical Swine Fever Virus (CSFV) E2 glycoprotein fused to the coat protein of potato virus X.

BACKGROUND: Classical Swine Fever (CSFV) is one of the most important viral infectious diseases affecting wild boars and domestic pigs. The etiological agent of the disease is the CSF virus, a single stranded RNA virus belonging to the family Flaviviridae. All preventive measures in domestic pigs have been focused in interrupting the chain of infection and in avoiding the spread of CSFV within wild boars as well as interrupting transmission from wild boars to domestic pigs. The use of plant based vaccine against CSFV would be advantageous as plant organs can be distributed without the need of particular treatments such as refrigeration and therefore large areas, populated by wild animals, could be easily covered. RESULTS: We report the in planta production of peptides of the classical swine fever (CSF) E2 glycoprotein fused to the coat protein of potato virus X. RT-PCR studies demonstrated that the peptide encoding sequences are correctly retained in the PVX construct after three sequential passage in Nicotiana benthamiana plants. Sequence analysis of RT-PCR products confirmed that the epitope coding sequences are replicated with high fidelity during PVX infection. Partially purified virions were able to induce an immune response in rabbits. CONCLUSION: Previous reports have demonstrated that E2 synthetic peptides can efficiently induce an immunoprotective response in immunogenized animals. In this work we have showed that E2 peptides can be expressed in planta by using a modified PVX vector. These results are particularly promising for designing strategies for disease containment in areas inhabited by wild boars.

Animals↗
PubMed2001

Oral immunization of pigs against classical swine fever. Course of the disease and virus transmission after simultaneous vaccination and infection.

The efficacy of simultaneous vaccination of pigs against classical swine fever (CSF) and challenge was evaluated. In this study, domestic weanling pigs were vaccinated orally with a conventional live virus vaccine based on CSF virus (CSFV) C strain and were challenged simultaneously with CSFV of different virulence. All the animals vaccinated and challenged with a high dose of highly virulent Koslov strain died while three of five animals challenged with a low dose of highly virulent Alfort 187 strain survived, shed the virus in nasal secretions, developed antibodies, and four of them showed a transient viremia. All the animals vaccinated and challenged with the low virulent field isolate MV 140/Riems survived, showed a short viremia and developed antibodies. No CSFV or CSFV RNA could be detected in the animals surviving the infection. This study demonstrates that oral vaccination of wild boars in an infected area bears no risk for the development of a persistent CSF infection.

Administration, Oral↗
PubMed2003

Infection of porcine reproductive and respiratory syndrome virus suppresses the antibody response to classical swine fever virus vaccination.

The effects of porcine reproductive and respiratory syndrome virus (PRRSV) infection on the antibody response to vaccination with classical swine fever (CSF) vaccine in piglets were investigated. Piglets were inoculated intranasally with the PRRSV BJ-4 strain, and then vaccinated intramuscularly with CSF vaccine 2 days later. Control animals were either vaccinated with CSF vaccine or infected with PRRSV alone. Time course of the antibody response against either PRRSV or CSF vaccine was measured. In animals infected with PRRSV prior to CSF vaccination, the antibody response to CSF vaccine was significantly lower than that observed in animals treated with CSF vaccination alone, especially during 3-5 weeks after vaccination. At the same time, no significant difference in serum PRRSV antibody level was observed between the animals treated with both PRRSV and CSF vaccine and the animals treated with PRRSV alone. These results suggested that the reduced antibody response against CSF vaccine observed in PRRSV-infected animals might be related to the higher prevalence of CSF in PRRSV prevalent farms in China.

Animals↗
PubMed2002

Simulated effect of pig-population density on epidemic size and choice of control strategy for classical swine fever epidemics in The Netherlands.

We examined the importance of pig-population density in the area of an outbreak of classical swine fever (CSF) for the spread of the infection and the choice of control measures. A spatial, stochastic, dynamic epidemiological simulation model linked to a sector-level market-and-trade model for The Netherlands were used. Outbreaks in sparsely and densely populated areas were compared under four different control strategies and with two alternative trade assumptions. The obligatory control strategy required by current EU legislation was predicted to be enough to eradicate an epidemic starting in an area with sparse pig population. By contrast, additional control measures would be necessary if the outbreak began in an area with high pig density. The economic consequences of using preventive slaughter rather than emergency vaccination as an additional control measure depended strongly on the reactions of trading partners. Reducing the number of animal movements significantly reduced the size and length of epidemics in areas with high pig density. The phenomenon of carrier piglets was included in the model with realistic probabilities of infection by this route, but it made a negligible contribution to the spread of the infection.

Animal Husbandry↗
PubMed1999

Virus antigen expression and alterations in peripheral blood mononuclear cell subpopulations after classical swine fever virus infection.

Depletion in the number of lymphocytes and viral persistence are thought to be the most important outcomes of classical swine fever virus (CSFV) infection. To define the change in peripheral blood mononuclear cells (PBMC) and virus replication in leukocytes after CSFV infection, 8-week old pigs were infected with the LPC vaccine strain or virulent CSFV (HCV-YL strain). Changes in the relative number of PBMCs were analyzed by flow cytometry. The results showed a significant increase in the relative percentage of monocytes in PBMCs during acute CSFV infection of naive pigs (p < 0.05). Monocyte frequencies were not changed in LPC-vaccinated pigs and control pigs. There was also a significant decrease in the number of IgM+ cells (p < 0.05) and a slight decrease in the number of CD4+ lymphocytes after 5 days of infection. There was no change in the frequency of CD8+ lymphocytes in PBMCs after infection. To define which subpopulation of PBMCs was the target for CSFV infection, PBMC populations from CSFV infected pigs were separated and stained for virus antigen expression. Alveolar macrophages (AM) were also studied. The results showed that CSFV replicated in all PBMC subpopulations: CD4+, CD8+, and IgM+ lymphocytes, and monocytes as well as AMs. However, virus antigen expression was more intense in monocytes and AMs. The infection of lymphocytes may, therefore, contribute to the depletion in their numbers after infection and lead to defective antibody production during virulent CSFV infection.

Animals↗
PubMed1998

Comparison of a reverse transcription-polymerase chain reaction assay and virus isolation for the detection of classical swine fever virus.

The authors evaluated the ability of a reverse transcription-polymerase chain reaction (RT-PCR) assay to detect classical swine fever virus (CSFV) in comparison with virus isolation and detection by an indirect immunoperoxidase assay (VI-IPA). To determine the specificity of the assay, samples from 60 spleens, 45 tonsils, ten submandibular lymph nodes, eight mesenteric lymph nodes and four kidneys, collected from pigs of various ages which had been slaughtered in abattoirs in Canada (a population free from CSFV), were tested. All the samples tested gave negative results by both VI-IPA and RT-PCR. A total of 20 samples were passaged in porcine kidney (PK) 15 cells and retested by both assays. All were found to be negative, giving a specificity of 100%. To determine the analytical sensitivity of the assay, a similar comparative study was conducted, using CSFV grown in tissue culture and tonsil tissues from a CSFV-infected pig. For both infected tissues and tissue culture fluids, RT-PCR was ten times more sensitive than VI-IPA. Amounts as small as 0.6 infectious units per 100 mg of tissue were detected by RT-PCR, compared to 6 infectious units by VI-IPA. Similarly, RT-PCR could detect as little as 0.1 infectious unit per ml in tissue culture fluids, compared to one infectious unit per ml by VI-IPA. To determine diagnostic sensitivity, three coded panels (two internal and one external), comprising 45 samples from 14 pigs, were tested. The diagnostic sensitivity of both RT-PCR and VI-IPA was found to be 100% for both internal panels. The results of the external panel, apart from two samples that were missed by both RT-PCR and VI-IPA, were found to be in total agreement. These two samples remained negative after amplification in PK15 cells. All the RT-PCR results were based on a single test whereas, for the VI-IPA results, positive results were obtained for five samples only after an amplification round in PK15 cells. Application of the RT-PCR assay for the diagnosis of CSFV would enable improved detection of the virus in a shorter time period.

Animals↗
PubMed1998

Infection with classical swine fever virus: effects on phenotype and immune responsiveness of porcine T lymphocytes.

T lymphocytes obtained from pigs infected with a lethal dose of classical swine fever virus were analysed for phenotypic changes in the composition of T-cell subpopulations and for alterations in their immune responsiveness in vitro during the course of disease. Viral antigen detected in all subpopulations and the selective depletion of CD4- CD8- gamma/delta T cells showed that peripheral blood T lymphocytes were affected in the terminal stage (14-19 days post-infection) of classical swine fever whereas no implications for T lymphocytes were obvious during the first 10 days after infection. Furthermore, a depletion of CD1+ CD4+ CD8+ 'common thymocytes' was characteristic for the infected animals. Studies on immune functions of peripheral T lymphocytes revealed an abrogation of cellular immune responses as early as 3-5 days after infection and thus before detection of viral antigens in these cells. The data suggest that early immunosuppression represents a crucial event for the manifestation of classical swine fever.

Animals↗
PubMed1999

A model to estimate the financial consequences of classical swine fever outbreaks: principles and outcomes.

A model is presented aimed at a financial analysis of a Classical Swine Fever outbreak. Financial consequences are calculated for affected parties, including governments (EU and national), farms, and related industries in the production chain. The model can be used to calculate the losses of a real outbreak as well as of a simulated one. In this article, the model is applied to the 1997/1998 outbreak of Classical Swine Fever in the Netherlands. Results show that total financial consequences of the outbreak are US $2.3 billion. Consequential losses for farmers and related industries are US $423 million and US $596 million respectively. Budgetary consequences for governments include less than 50% of the total losses calculated by the model. The model can be adapted easily to suit other diseases and countries.

Animal Husbandry↗
PubMed2006

Recombination and expression of classical swine fever virus (CSFV) structural protein E2 gene in Chlamydomonas reinhardtii chroloplasts.

The expression of classical swine fever virus (CSFV) structural protein E2 in different vectors, which has been shown to carry critical epitopes, has been established. Here, we reported a Chlamydomonas reinhardtii chloroplast expression vector, P64E2, containing classical swine fever virus structural protein E2 gene, which was constructed and transferred to C. reinhardtii by biolistic bombardment method. The transformants were identified by PCR, Southern blotting, Western blotting after selecting on resistant media. ELISA quantification assay showed that the expressed E2 protein accumulated up to 1.5-2% of the total soluble protein. The results of the study on the immunological activity indicated that the protein E2 expressed in C. reinhardtii chloroplasts could elicit animal bodies to produce antibodies against protein E2.

Animals↗
PubMed2004

Development of maternal antibodies after oral vaccination of young female wild boar against classical swine fever.

An experimental study was performed to investigate the development of maternal antibodies after oral immunisation of young female wild boar against classical swine fever (CSF) using C-strain vaccine. Our results demonstrated that maternal antibodies do not persist in the offspring for more than 3 months. Based on the neutralising serum antibody titres, we assume that piglets of wild sows vaccinated orally twice or immunised once a long time before conception have protective antibodies for approximately 2 months. Furthermore, it seems that the level and the duration of maternal antibodies in the offspring are depend on the age of the female animals at the moment of vaccination as demonstrated in our experiment. The recent vaccination procedure consists of three double vaccinations in spring, summer and autumn. Especially vaccinations in summer and autumn could be crucial for transfer of high maternal antibody titres to the offspring.

Animals↗
PubMed2005

Evolution of T lymphocytes and cytokine expression in classical swine fever (CSF) virus infection.

This study characterized the cell-mediated immune response in pigs inoculated with the Alfort 187 isolate of classical swine fever (CSF) virus. Quantitative changes in the T-lymphocyte population (CD3(+), CD4(+) and CD8(+)) and qualitative changes in cytokine expression (IL-2, IL-4 and IFNgamma) by these cells in serum, thymus and spleen were demonstrated. These changes coincided spatially and temporally with previously described quantitative and qualitative changes in monocyte-macrophage populations, thus demonstrating the contribution of the two cell populations to lymphoid depletion. Moreover, examination of cytokine expression in thymus and spleen samples revealed a type 1 cell-mediated immune response in the early and middle stages of the experiment, giving way to a type 2 immune response towards the end of the experiment; these findings, which accorded with the serological results and lymphopenia, may influence the delayed humoral response characteristic of CSF.

Animals↗
PubMed2002

Apoptosis of thymocytes related to cytokine expression in experimental classical swine fever.

Atrophy of the thymic cortex and loss of thymocytes were studied in 32 pigs inoculated with the virulent strain "Alfort" of classical swine fever (CSF) virus and killed at intervals from 2 to 15 days after infection. Immunohistochemical, ultrastructural, ELISA and TUNEL methods were used. The results suggested that direct action of CSF virus on thymocytes played no more than a minor role. The massive lymphoid depletion observed in the thymus, may, however, have been associated with the numerical increase in monocytes-macrophages in this organ, and their secretory activation, leading to synthesis and release of tumour necrosis factor (TNF)-alpha, interleukin (IL)-1alpha and C1q complement component as main chemical mediators, and IL-1beta and IL-6 as minor mediators. These cytokines (TNF-alpha and IL-1alpha) may have played a role in the apoptosis of thymocytes, demonstrated by TUNEL and ultrastructural methods. The pathogenetic mechanism outlined may contribute to the lymphoid depletion observed in others organs in CSF and may explain the lymphopenia characteristic of the disease.

Animals↗
PubMed2004

Attenuation of classical swine fever virus by deletion of the viral N(pro) gene.

We have reported earlier that replacement of the N(pro) gene of classical swine fever virus (CSFV) by the murine ubiquitin gene only slightly affects the characteristics of virus replication in the porcine kidney cell line SK-6 [J. Virol. 72 (1998) 7681]. Here, for the moderately virulent CSFV strain Alfort/187 as well as for the highly virulent strain Eystrup we show that the respective N(pro)-deleted viruses are attenuated. Vaccination of pigs with either of the two deletion mutants resulted in the induction of a strong antibody response. Animals were protected against challenge with a lethal dose of highly virulent CSFV indicating that N(pro) deletion mutants are excellent candidates for a modified live virus vaccine. A chimeric virus obtained by replacement of the N(pro) gene in the Eystrup virus by the corresponding sequence of the avirulent CSFV vaccine strain Riems resulted in a virus that was highly virulent. This indicates that the virulence of CSFV correlates with the presence of N(pro) and also suggests that N(pro) is not responsible for the varying virulence observed between individual strains of CSFV.

Animals↗