Chimeric (marker) C-strain viruses induce clinical protection against virulent classical swine fever virus (CSFV) and reduce transmission of CSFV between vaccinated pigs

Two live recombinant vaccines (Flc9 and Flc11) against classical swine fever (CSF) were evaluated for their capacity to reduce transmission of virulent CSF virus (CSFV) among vaccinated pigs. In Flc9 the 5' terminal half of the E2 gene of the C-strain, a CSFV vaccine strain, was exchanged with the homologous gene of the bovine viral diarrhoea virus (BVDV) strain 5250, the E(rns) gene was exchanged likewise in the chimeric Flc11 virus. Both recombinant vaccines induce an antibody response in pigs that can be distinguished from that induced after a wild-type CSFV infection. Four experiments were performed to estimate the reproduction ratio R after different vaccination-challenge intervals. Each group consisted of ten pigs [specified pathogen free (SPF) pigs or conventional pigs] that were vaccinated once, intramuscularly, either with Flc9 or Flc11 virus or that were not vaccinated. Vaccinated and susceptible pigs were challenged intranasally with the virulent CSFV strain Brescia or Behring, 1, 2 or 4 weeks after vaccination. Whether contact-pigs became infected was determined using a CSFV specific E2 (Flc9) or E(rns) (FLc11) antibody ELISA. In the unvaccinated control groups, virus secretion started from day 2 to 4 after inoculation and all contact pigs became infected. Contact pigs became infected in the group of pigs (SPF or conventional) vaccinated once with Flc9 virus and challenged 1-, 2- or 4-weeks later. The estimates of the R in the groups challenged at 1-, 2- and 4-weeks after vaccination were 0.38, 0 and 0.75, respectively. Contact infected pigs were not detected (R=0) in any of the groups of pigs, vaccinated with Flc11, only SPF pigs were used. In order to achieve a statistical significance of R within the vaccinated groups each of the experiments has to be repeated at least once. The R of pigs vaccinated with Flc11 virus and challenged at 1- or 2-weeks after vaccination was however significantly lower that the reproduction ratio of the unvaccinated groups (P=0.013). The R of pigs vaccinated with Flc9 virus and challenged at 1 (conventional pigs) or 2 weeks (SPF pigs) after vaccination was significantly lower that the reproduction ratio of the unvaccinated groups (P=0.013). In conclusion, both chimeric viruses Flc9 and Flc11 provided good clinical protection against a challenge with virulent CSFV at 1 or 2 weeks after vaccination. Further experiments should be carried out to study more aspects of the efficacy of these recombinant viruses before they can be used as a marker vaccine under field circumstances.     

Chinese border disease virus strain JSLS12-01 infects piglets and down-regulates the antibody responses of classical swine fever virus C strain vaccination

During 2012 and 2013, several border disease virus (BDV) strains were identified from Chinese goat and sheep herds. At the same time, pigs from the same areas were found to be seropositive to BDV by ELISA, without showing clinical signs (unpublished data). To examine the susceptibility of pigs to the Chinese BDV strains, BDV isolate JSLS12-01, isolated from naturally infected sheep, was used to infect pigs. Antibody responses, viremia, clinical signs and pathological changes of the infected animals were examined. It confirmed that the current BDV strain could infect the domestic pigs, the animals showed viremia during 4 to 14 days post infection (dpi) and sero-conversion from 14 dpi; no clinical and pathological changes were observed. In addition, CSFV maternal antibody did not influence BDV infection. Subsequently, pigs were infected with the BDV isolate and vaccinated with Hog cholera lapinized virus (HCLV) 21 days later to determine the effect of BDV infection on antibody induction of CSFV vaccination. The specific CSFV antibody and neutralizing antibody titers of the BDV infected group remained negative after the primary vaccination. Even after the boost vaccination, they were still significantly lower than those of the uninfected groups (p < 0.05). These results indicated that BDV infection could down-regulate the antibody responses of CSFV C-strain vaccination. It should be paid attention that BDV prevalence in pig herds and in live vaccines might hamper the vaccination of CSF.     

CP7_E2alf: a safe and efficient marker vaccine strain for oral immunisation of wild boar against Classical swine fever virus (CSFV)

Wild boar are an important reservoir of Classical swine fever virus (CSFV) in several European countries, where most of the primary outbreaks in domestic pigs are directly related to the endemic disease situation in the wild boar population. Oral immunisation has been introduced as an additional control measure to accelerate CSF eradication in wild boar in Germany since 1993. Immunisation with an oral bait vaccine based on the conventionally attenuated live vaccine strain "C" proved to be safe and effective, but does not allow differentiation between infected and vaccinated animals. Therefore, we examined the vaccine efficacy of the recently constructed chimeric pestivirus CP7_E2alf, whose coding sequences for the major envelope protein E2 of BVDV strain CP7 are replaced by E2 of the CSFV strain Alfort187 [Reimann I, Depner K, Trapp S, Beer M. An avirulent chimeric pestivirus with altered cell tropism protects pigs against lethal infection with classical swine fever virus. Virology 2004;322(1):143-57]. Following oral immunisation of wild boar, CP7_E2alf proved to be completely avirulent. Furthermore, all vaccinees were fully protected from clinical disease after a highly virulent CSFV challenge infection. The immunised animals seroconverted within 3 weeks after vaccination for CSFV E2-specific and CSFV neutralising antibodies, whereas prior to challenge infection no antibodies against CSFV E(rns) were detected with an appropriate CSFV-specific marker ELISA test. Thus, the BVDV backbone of CP7_E2alf enables serological and genetic differentiation from wild type CSFV infection. In conclusion, CP7_E2alf represents the first efficient and safe marker vaccine candidate for oral immunisation of wild boar against CSFV.     

Efficacy and safety of simultaneous vaccination with two modified live virus vaccines against porcine reproductive and respiratory syndrome virus types 1 and 2 in pigs

The objective of the study was to compare responses of pigs vaccinated with a PRRS MLV vaccine against PRRSV-1 or PRRSV-2 with the responses of pigs vaccinated simultaneously with both vaccines. Furthermore, the efficacy of the two PRRSV MLV vaccination strategies was assessed following challenge. The experimental design included four groups of 4-weeks old SPF-pigs. On day 0 (DPV0), groups 1–3 (N = 18 per group) were vaccinated with modified live virus vaccines (MLV) containing PRRSV-1 virus (VAC-T1), PRRSV-2 virus (VAC-T2) or both (VAC-T1T2). One group was left unvaccinated (N = 12). On DPV 62, the pigs from groups 1–4 were mingled in new groups and challenged (DPC 0) with PRRSV-1, subtype 1, PRRSV-1, subtype 2 or PRRSV-2. On DPC 13/14 all pigs were necropsied. Samples were collected after vaccination and challenge. PRRSV was detected in all vaccinated pigs and the majority of the pigs were positive until DPV 28, but few of the pigs were still viremic 62 days after vaccination. Virus was detected in nasal swabs until DPV 7–14. No overt clinical signs were observed after challenge. PRRSV-2 vaccination resulted in a clear reduction in viral load in serum after PRRSV-2 challenge, whereas there was limited effect on the viral load in serum following challenge with the PRRSV-1 strains. Vaccination against PRRSV-1 had less impact on viremia following challenge. The protective effects of simultaneous vaccination with PRRSV Type 1 and 2 MLV vaccines and single PRRS MLV vaccination were comparable. None of the vaccines decreased the viral load in the lungs at necropsy. In conclusion, simultaneous vaccination with MLV vaccines containing PRRSV-1 and PRRSV-2 elicited responses comparable to single vaccination and the commercial PRRSV vaccines protected only partially against challenge with heterologous strains. Thus, simultaneous administration of the two vaccines is an option in herds with both PRRSV types.     

Experimental non-transmissible marker vaccines for classical swine fever (CSF) by trans-complementation of E(rns) or E2 of CSFV

Three mutants with deletions in the E2 gene of the infectious DNA copy of the classical swine fever virus (CSFV) strain-C were constructed: one missing the B/C domain of CSFV-E2 between amino acids (aa) 693 and 746, one missing the A domain between aa 800 and 864, and one missing the complete E2 between aa 689 and 1062. All three CSFV-E2 deletion mutants were unable to generate viable virus, indicating that each of the antigenic domains of E2 is essential for viability of CSFV. To rescue the CSFV-E2 deletion mutants SK6 cell lines constitutively expressing glycoprotein E2 of CSFV were generated. The rescued viruses infected and replicated in SK6 cells as demonstrated by expression of viral proteins, but this primary infection did not result in reproduction of infectious virus. Thus, these E2 complemented viruses are considered non-transmissible. In previous experiments, we showed that simultaneous injection of E(rns) complemented virus (Flc23) via intradermal (ID), intramuscular (IM) or intranasal (IN) routes conferred protection to pigs against a lethal challenge with CSFV [J. Virol. 74 (2000) 2973]. Here, we evaluate different routes of application (ID, IM or IN) with E(rns) complemented virus Flc23 in order to find the best route for complemented CSFVs. Intradermal injection with Flc23 protected pigs against a lethal CSFV challenge, whereas intramuscular injection induced partial protection, and intranasal injection did not mediate a protective immune response in pigs at all. We used the intradermal route of vaccination to test the E2 complemented viruses. Vaccination of pigs via the intradermal route with the E2 complemented CSFVs also resulted in the induction of antibodies and in (partial) protection against CSFV challenge. Pigs vaccinated with E2 complemented virus Flc4 (deletion B/C domain) survived a lethal CSFV challenge, whereas partial protection was induced in pigs vaccinated with Flc47 (deletion E2) or Flc48 (deletion A domain) E2 complemented viruses. Serological data demonstrate that these E2 complemented mutant viruses are, in combination with well known diagnostic tests based on E2, potential marker vaccines for CSF.     

Immunization of pigs with a type 2 modified live PRRSV vaccine prevents the development of a deadly long lasting hyperpyrexia in a challenge study with highly pathogenic PRRSV JX143

Porcine reproductive and respiratory syndrome virus (PRRSV) has been confirmed to be the underlying cause of the so-called ‘porcine high fever disease’ (PHFD), a disease that emerged in China in 2006 and subsequently spread over South East Asia. The aim of this study was to investigate whether animals challenged with the Chinese highly pathogenic PRRSV JX143 would be protected by vaccination with single dose of a type 2 modified live virus (MLV) vaccine. Forty-four pigs 17–19 days of age were weighed and randomly assigned to either vaccination with subsequent challenge (V/C, n = 20), challenge only (NV/C, n = 12) and no vaccination and no challenge (strict controls, n = 12). Pigs of the challenged groups (V/C and NV/C) were inoculated intranasally 27 days post-vaccination with PRRSV JX143. Animals were monitored during the subsequent 21 days post challenge and were necropsied at the end of the experiment on day 49. Observations and measurements included body temperature, clinical scores for behavior/general condition, cough and breathing pattern, mortality, serological response and PRRSV viremia via RNA detection. Challenge in the NV/C pigs resulted in 100% morbidity and 67% mortality whereas all vaccinated pigs survived. There was a close association between hyperpyrexia (fever over 41 °C) and incidence in mortality, which was completely prevented by vaccination. Clinical symptoms were less severe, and of transient nature only, in the vaccinated pigs. Vaccination did not prevent infection, but reduced the impact of clinical disease and prevented hyperpyrexia associated mortality.     

Immune duration of a recombinant PRRSV vaccine expressing E2 of CSFV

Classical swine fever virus (CSFV) and Porcine reproductive and respiratory syndrome virus (PRRSV) are both important pathogens which seriously harm the economic swine industry worldwide. We have previously demonstrated that rPRRSV-E2 is a promising live, virus-vectored vaccine that provides 100% protection against highly pathogenic PRRSV (HP-PRRSV) and CSFV. Here, we evaluated the duration of immunity (DOI) of the vaccine strain, rPRRSV-E2. Vaccine or cell culture medium was administered to piglets at 4 weeks of age. All immunized piglets developed high levels of antibodies, which could maintain for up to 23 weeks, against PRRSV and CSFV. All immunized pigs were well protected from the challenge of HP-PRRSV or CSFV at 20 weeks and 24 weeks post vaccination. The vaccine protection rate was still 100% at 24 weeks after immunization. The immune efficacy results showed that the immune duration of rPRRSV-E2 could be up to 5 months.     

Antibody responses following vaccination versus infection in a porcine circovirus-type 2 (PCV2) disease model show distinct differences in virus neutralization and epitope recognition

Porcine circovirus associated disease (PCVAD) encompasses a group of syndromes linked to infection with porcine circovirus type 2 (PCV2). Based on the hypothesis that the immune responses to vaccination versus infection are quantitatively and qualitatively different, the objective of this study was to evaluate immunity, virus replication and disease protection in pigs vaccinated with PCV2 capsid protein (CP) and during infection. The disease model included dual infection with PCV2 and porcine reproductive and respiratory syndrome virus (PRRSV), a virus known to enhance disease progression and severity. The principal effect of PRRSV infection was to increase peak PCV2 viremia by almost 40-fold; however, PCV2 failed to show a reciprocal effect on PRRSV. In vaccinated pigs, there was no evidence of disease or PCV2 replication following dual virus challenge. Immunity following vaccination favored PCV2 neutralizing activity; whereas, PCV2 infection and disease produced high levels of non-neutralizing antibody, primarily directed against a polypeptide in the C-terminal region of CP. These results support the notion that the magnitude of the total antibody response cannot be used as a measure of protective immunity. Furthermore, protection versus disease lies in the immunodominance of specific epitopes. Epitope specificity should be taken into consideration when designing PCV2 vaccines.     

The impact of porcine circovirus associated diseases on live attenuated classical swine fever vaccine in field farm applications

Porcine circovirus associated diseases (PCVADs) are among the most important diseases affecting the worldwide swine industry. Vaccination against porcine circovirus type 2 (PCV2) infection has been utilized for disease control and effectively reduces clinical signs of PCVADs. To evaluate the efficacy of the PCV2 vaccine in field farms, we conducted a trial using conventional pigs immunized with the subunit PCV2 vaccine followed by PCV2 challenge. Immunized pigs demonstrated lower serum viral loads, less viral antigen staining in lymph nodes, and higher average daily weight gain, confirming the protective efficacy of the vaccine. However, low levels of PCV2 infection were still detected in vaccinated pigs after challenge, suggesting that the PCV2 vaccine was unable to eradicate the virus, which could lead to asymptomatic PCV2 subclinical infection (PCV2-SI) in pig farms. Additionally, PCV2 infection is a risk factor for impaired pig immune response development during the weaning to growth stages, which is a crucial period to receive vaccines against classical swine fever (CSF). Therefore, the impact of PCV2-SI or PCV2-systemic disease (PCV2-SD) on live attenuated CSF vaccine was investigated. After PCV2 challenge, there was no difference in levels of classical swine fever virus (CSFV) neutralizing antibodies (NA) between pigs with PCV2-SD and PCV2-SI, suggesting that the efficacy of CSF vaccine was compromised. Moreover, results of long-term monitoring of CSFV NA titers in PCV2-SI pigs with minimized interference by maternally-derived antibodies suggested that serum PCV2 viral loads greater than 10² copies/mL may compromise the efficacy of CSF vaccine. Overall, a conventional pig model was established to demonstrate the impaired efficacy of the subunit PCV2 vaccine and its impact on the CSF vaccine in vaccination-challenge trials. Additionally, the impaired efficacy of the PCV2 vaccine resulted in increased PCV2-SI, eventually leading to compromised the live attenuated CSF vaccine induced NA response in field farm applications.     

Marker vaccine strategies and candidate CSFV marker vaccines

Classical swine fever (CSF) is an economically important highly contagious disease of swine worldwide. Classical swine fever virus (CSFV) is its etiological agent, and the only natural hosts are domestic pigs and wild boars. Although field CSFV strains vary in the virulence, they all result in serious losses in pig industry. Highly virulent field strains generally cause acute disease and high mortality; moderately virulent field strains raise subacute or chronic infections; postnatal infection by low virulent field strains produces subclinical infection and mortality in the new-born piglets. CSFV can cross the placental barrier, and this transplacental transmission usually results in mortality of fetuses and birth of congenitally infected pigs with a late-onset disease and death. Two main strategies to control CSF epidemic are systematic prophylactic vaccination with live attenuated vaccines (such as C-strain) and non-vaccination stamping-out policy. But neither of them is satisfying enough. Marker vaccine and companion serological diagnostic test is thought to be a promising strategy for future control and eradication of CSF. During the past 15 years, various candidate marker vaccines were constructed and evaluated in the animal experiments, including recombinant chimeric vaccines, recombinant deletion vaccines, DNA vaccines, subunit vaccines and peptide vaccines. Among them, two subunit vaccines entered the large scale marker vaccine trial of EU in 1999. Although they failed to fulfil all the demands of the Scientific Veterinary Committee, they successfully induced solid immunity against CSFV in the vaccinated pigs. It can be expected that new potent marker vaccines might be commercially available and used in systematic prophylactic vaccination campaign or emergency vaccination in the next 15 years. Here, we summarized current strategies and candidate CSFV marker vaccines. These strategies and methods are also helpful for the development of new-generation vaccines against other diseases.     

Evaluation of the intranasal route for porcine reproductive and respiratory disease modified-live virus vaccination

BackgroundIn pigs, modified live virus (MLV) vaccines against porcine reproductive and respiratory syndrome virus (PRRSV) are commonly used and administered by intramuscular (IM) injection. In contrast, PRRSV, as a primary respiratory pathogen, is mainly transmitted via the intranasal (IN) route. The objective of this study was to evaluate the efficacy of a commonly used commercial PRRSV MLV delivered IN compared to the IM route.MethodsFifty-four pigs were divided into five treatment groups. All vaccinated groups received the same MLV vaccine but administered via different routes. Group IN-JET-VAC was vaccinated with an automated high pressure prototype nasal jet device (IN-JET-VAC, n = 12), group IN-MAD-VAC was vaccinated with a mucosal atomization device (IN-MAD-VAC, n = 12), group IM-VAC was vaccinated intramuscularly (IM-VAC; n = 12) according to label instructions, while the NEG-CONTROL (n = 6) and the POS-CONTROL (n = 12) groups were both unvaccinated. At 28 days post vaccination all vaccinated groups and the POS-CONTROL pigs were challenged with a pathogenic US PRRSV isolate. Blood and nasal swabs were collected at regular intervals, and all pigs were necropsied at day 10 post challenge (dpc) when gross and microscopic lung lesions were assessed.ResultsPrior to challenge most vaccinated pigs had seroconverted to PRRSV. Clinical signs (fever, inappetence) were most obvious in the POS-CONTROL group from dpc 7 onwards. The vaccinated groups were not different for PRRSV viremia, seroconversion, or average daily weight gain. However, IN-JET-VAC and IN-MAD-VAC had significantly higher neutralizing antibody levels against the vaccine virus at challenge.ConclusionsComparable vaccine responses were obtained in IN and IM vaccinated pigs, suggesting the intranasal administration route as an alternative option for PRRSV vaccination.     

Efficacy of an attenuated European subtype 1 porcine reproductive and respiratory syndrome virus (PRRSV) vaccine in pigs upon challenge with the East European subtype 3 PRRSV strain Lena

The efficacy of a commercial attenuated European subtype 1 PRRSV vaccine was evaluated upon challenge with the East European subtype 3 PRRSV strain Lena (83.3% nucleotide identity). Two vaccination experiments were carried out. Four- and seven-week-old pigs were vaccinated with the modified-live vaccine. Upon vaccination, virus specific IPMA antibodies were detected in all vaccinated animals with titers ranging from 10^2.8 to 10^4.6. No virus neutralizing (VN) antibodies were detected after vaccination. Eight (exp. 1) or six (exp. 2) weeks after vaccination, pigs were challenged with 10⁶ (exp. 1) resp. 10⁵ (exp. 2) TCID₅₀ of the European subtype 3 PRRSV Lena. Upon challenge, non-vaccinated animals showed fever during 5.1 (exp. 1) or 7.7 (exp. 2) days. In vaccinated pigs, the duration of fever was reduced by 1.8 (exp. 1) or 3.5 (exp. 2) days. The modified-live virus vaccine reduced the mean duration of nasal shedding and viremia. In non-vaccinated pigs, virus shedding lasted 5.8 days (exp. 1), resp. 8.3 days (exp. 2). This period was reduced to 3.6 (exp. 1), resp. 3.0 (exp. 2) days in vaccinated animals. Viremia was observed during a shorter period in vaccinated (exp. 1: 7.4 days, exp. 2: 4.8 days) than in non-vaccinated groups (exp. 1: 11.8 days, exp. 2: 12.3 days). Starting from 5 days post challenge, virus titers in nasal secretions and sera were significantly lower in vaccinated animals (P < 0.05). Virus-neutralizing antibodies were detected at low titers (≤16) after 7 days post challenge in vaccinated animals and 28 days post challenge in control animals. In conclusion, it can be stated that vaccination of pigs with an attenuated European subtype 1 vaccine provides a partial protection against a subsequent exposure to the highly pathogenic East European subtype 3 PRRSV strain Lena.     

Protection and immune response in pigs intradermally vaccinated against porcine reproductive and respiratory syndrome (PRRS) and subsequently exposed to a heterologous European (Italian cluster) field strain

The purpose of this study was to assess the immune response in pigs intradermally vaccinated with a commercially available attenuated porcine reproductive and respiratory virus (PRRSV) vaccine (Porcilis PRRS) and subsequently exposed to a heterologous (Italian cluster) field strain of virulent PRRSV. A total of 18, 4-week-old pigs seronegative for PRRSV were allocated to 1 of 3 groups (groups A, B, and C). At 5 weeks of age, pigs of groups A (n=6 pigs) and B (n=6 pigs) were vaccinated intramuscularly and intradermally, respectively, with Porcilis PRRS. The more conventional intramuscular route of vaccination was included for comparative purposes with the intradermal route of vaccination (performed with the I.D.A.L. vaccinator). Pigs of group C (n=6 pigs) were kept as nonvaccinated controls. At post-vaccination (PV) days 7, 14, 21, 28, and 35, blood samples were collected for detection of vaccine virus (PCR) and antibodies (ELISA), and for changes in PBMC (flow cytometry). At PV day 35, pigs of all groups were each exposed (challenged) intranasally to a heterologous field strain (78% ORF5 sequence homology between vaccine and field virus) belonging to the Italian cluster of the European genotype of PRRSV. At post-challenge (PC) days 0, 3, 7, 10, 13, and 17, blood samples were collected for detection and quantitation of virus and antibodies, and for changes in PBMC as described above for blood samples collected PV. Throughout the experiment all pigs were observed daily for clinical signs. At PC days 7 and 17, two pigs and four pigs, respectively, of each group were euthanized and examined for macroscopic lesions. Following vaccination some pigs of groups A and B had a detectable viremia that in two pigs (one pig of group A and one pig of group B) lasted until PV day 28. However, all pigs (groups A, B, and C) remained clinically normal. All vaccinated pigs developed a serological response (ELISA) to PRRSV. Presumptive evidence for vaccine-induced protective immunity against the heterologous challenge strain was provided by finding that viremia following challenge was generally less (incidence) and significantly less (titers) in vaccinated pigs than in nonvaccinated pigs. No differences were apparent between pigs vaccinated intramuscularly and those vaccinated intradermally. The absence of virulent-virus-induced clinical signs and macroscopic lesions in nonvaccinated as well as in vaccinated pigs precluded a more definitive evaluation of the magnitude of protective immunity provided by vaccination or by the route of vaccination. Some likely treatment-associated changes in lymphocyte subpopulations were observed among the three treatment groups. These changes and their potential relationship to protective immunity are discussed.     

Determination of the onset of the herd-immunity induced by the E2 sub-unit vaccine against classical swine fever virus

For a recently developed E2 subunit vaccine against classical swine fever (CSF), the reduction in transmission, at different moments after vaccination, was assessed by animal experiments and statistical calculations. Two experiments were performed to estimate the reproduction ratio R. Experiment 1 consisted of three groups and experiment 2 of two groups each of 10 pigs. In four of these groups, all pigs were vaccinated intramuscularly with the vaccine. The pigs in the fifth group remained unvaccinated (control group). After treatment, half of each group was intranasally inoculated with the virulent CSFV strain Brescia. In the vaccine groups, the following vaccination-challenge intervals were applied: 14, 14, 10, and 7 days, respectively. The occurrence of (contact-) infection was determined using the E(rns) ELISA. In the 7-days interval group and in the control group, virus transmission to all contact pigs occurred, indicating R1. Neither in the two 2-week interval groups nor in the 10-day interval group did contact-infections occur. Hence, the estimated R is less than one, which indicates that an epidemic would fade out. Therefore, the E2 subunit vaccine may be an efficacious tool in a control program during an outbreak of CSF as from 10 days after vaccination.     

Deoxynivalenol (DON) naturally contaminated feed impairs the immune response induced by porcine reproductive and respiratory syndrome virus (PRRSV) live attenuated vaccine

Cereal commodities are frequently contaminated with mycotoxins produced by the secondary metabolism of fungal infection. Among these contaminants, deoxynivalenol (DON), also known as vomitoxin, is the most prevalent type B trichothecene mycotoxin worldwide. Pigs are very sensitive to the toxic effects of DON and are frequently exposed to naturally contaminated feed. Recently, DON naturally contaminated feed has been shown to decrease porcine reproductive and respiratory syndrome virus (PRRSV) specific antibody responses following experimental infection. The objective of this study was to determine the impact of DON naturally contaminated feed on the immune response generated following vaccination with PRRSV live attenuated vaccine. Eighteen pigs were randomly divided into three experimental groups of 6 animals based on DON content of the diets (0, 2.5 and 3.5 mg DON/kg). They were fed these rations one week prior to the vaccination and for all the duration of the immune response evaluation. All pigs were vaccinated intra-muscularly with one dose of Ingelvac^® PRRSV modified live vaccine (MLV). Blood samples were collected at day −1, 6, 13, 20, 27 and 35 post vaccination (pv) and tested for PRRSV RNA by RT-qPCR and for virus specific antibodies by ELISA. Results showed that ingestion of DON-contaminated diets significantly decreased PRRSV viremia. All pigs fed control diet were viremic while only 1 (17%) and 3 (50%) out of 6 pigs were viremic in the groups receiving 3.5 and 2.5 mg of DON/kg, respectively. Subsequently, all pigs fed control diet developed PRRSV specific antibodies while only viremic pigs that were fed contaminated diets have developed PRRSV specific antibodies. These results suggest that feeding pigs with DON-contaminated diet could inhibit vaccination efficiency of PRRSV MLV by severely impairing viral replication.     

Vaccination influences the evolution of classical swine fever virus

Classical swine fever is a serious, economically damaging disease caused by classical swine fever virus (CSFV). The CSFV is composed of two clades, according to phylogenetic estimates. Attenuated live vaccine such as HCLV, has been widely used to protect pigs from CSFV, but the influence of vaccination on the evolution of CSFV has not been studied. We conducted a systemic analysis of the impact of vaccination on the evolution of CSFV by comparing vaccine-related and non-vaccine-related CSFV groups. We found that vaccination may affect strain diversity and immune escape through recombination and point mutation. We also found that vaccination may influence the population dynamics, evolutionary rate and adaptive evolution of classical swine fever virus. Our evidence suggests that the vaccination might also change host adaptation through influencing codon usage of the virus in swine. These findings suggest that it is necessary to avoid excessive use of CSFV attenuated vaccines.     

A DNA vaccine expressing the E2 protein of classical swine fever virus elicits T cell responses that can prime for rapid antibody production and confer total protection upon viral challenge

Immunization of domestic pigs with a DNA vaccine expressing the complete E2 protein of classical swine fever virus (CSFV) conferred total protection against a severe viral challenge. Immunization with three doses of plasmid pcDNA3.1/E2 elicited a consistent and specific, MHC class II restricted T cell response in the three domestic pigs analyzed, in the absence of detectable anti-CSFV antibodies in serum. Upon challenge specific T cell responses were boosted in the three vaccinated pigs, and a rapid rise in the titers of CSFV neutralizing antibodies was noticed in two of them, which correlated with a total protection. In these two pigs, neither disease symptoms were observed nor was virus detected at any time after CSFV infection. Neutralizing antibody titers were lower in the third vaccine, which developed a mild and transient peak of pyrexia. As expected, similar analyses in three control pigs (injected with the empty vector or PBS) did not reveal the induction of specific T cells or viral antibodies and, upon challenge, animals developed severe symptoms of the disease, including high titers of viremia, hyperthermia and virus spread to different organs. Control pigs developed, also, a marked leucopenia, resulting in SWC3+ (myelomonocytic cells) being the major PBMC population, and a drastic decrease CD3+ T cells. This T cell depletion was prevented in animals immunized with pcDNA3.1/E2. The total protection achieved, in the absence of CSFV antibodies before challenge, supports the relevance in the antiviral response observed of specific T cell responses primed by pcDNA3.1/E2 vaccine, which, upon challenge, led to a rapid induction of neutralizing antibodies. The observation that CSFV antibodies could only be detected in protected animals after viral challenge opens the possibility of exploring the potential of the DNA vaccine approach used to develop marker vaccines against CSF.