Selection and Evaluation of Porcine circovirus (PCV) 2d Vaccine Strains to Protect against Currently Prevalent PCV2.

Porcine circovirus (PCV) 2d is a common genotype in South Korea, and the cross-protective ability of PCV2a-based vaccines has been reported recently. In this study, a PCV2d vaccine candidate was selected, and its protective efficacy against the PCV2d isolate was evaluated. From 2016 to 2020, 234 PCV2d isolates were phylogenetically analyzed using open reading frame 2 (ORF2) sequences and classified into four subgroups: PCV2d-1, PCV2d-2, PCV2d-3, and PCV2d-4. Except for PCV2d-4, which consisted of ungrouped isolates, the three subgroups showed distinct differences at amino acid positions 53 and 169 in the ORF2. The detection rates of PCV2d-1, PCV2d-2, and PCV2d-3 were 36.5, 37.4, and 3.7%, respectively, and representative isolates were selected from each subgroup (QIA244, QIA126, and QIA169, respectively). In the neutralization assay, QIA244 showed the lowest neutralization efficiency among the three PCV2a-based vaccines, whereas the virus-like particles of QIA244 (rQIA244) provided broader protection against the three genotypes than did those of QIA126 and rQIA169. To further evaluate rQIA244 in pigs, the experimental groups were divided into rQIA244-vaccine (2dVac), commercial PCV2a-vaccine (2aVac), and no-vaccination (noVac) groups. The 2dVac effectively reduced the copy number of PCV2d in blood and tissues, as well as in tissue lesions, compared to the effect of 2aVac. Collectively, 2dVac provided by QIA244 ORF2 successfully demonstrated protective efficacy against the currently prevalent PCV2d in vitro neutralization and in vivo assays.

A Field Efficacy Trial of Recombinant Porcine Circovirus Type 2d Vaccine in Three Herds.

This study aimed to evaluate the efficacy of a virus-like particle (VLP) vaccine containing the open reading frame 2 of porcine circovirus type 2d (PCV2d) in a farm environment where natural infections associated with porcine circovirus-associated disease are endemic. The vaccine trial was conducted on three farms (H, M, and Y) with a history of infections including porcine reproductive and respiratory syndrome virus (PRRSV), PCV, Mycoplasma, and E. coli. Farm H, as well as farms M and Y, experienced natural PCV2 infection between 4 and 8 weeks post-vaccination (wpv), and 8 and 12 wpv, respectively. Viremia levels of all farms were significantly (p < 0.05) lower in vaccinated piglets than the control group after natural infection. In all farms, serum immunoglobulin G levels peaked at 8 wpv in the vaccinated groups, surpassing those in the control groups. Furthermore, neutralizing antibody titers were significantly (p < 0.05) higher in the vaccinated groups than the control groups in farms H and Y (0-8 wpv). However, there were no significant differences between the vaccinated and control group in neutralizing antibody titers of farm M (0-20 wpv). In terms of body weight, vaccinated piglets from all three farms showed significantly increased average weights at 12 wpv compared to the control groups. In conclusion, our study revealed noteworthy differences in viremia and body weight gain between vaccinated and control animals on three farms. As a result, this field trial of PCV2d VLP vaccine was successful in protecting piglets from natural PCV2 infection.

A novel chimeric vaccine candidate for porcine reproductive and respiratory syndrome virus (PRRSV) I and II elicits neutralizing antibodies against both types.

Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically important virus within the swine industry. The virus causes respiratory disease and reproductive failure. Two species of PRRSV-I and II are co-dominant, yet no effective vaccination strategy has been developed to protect against these two types. With an aim to develop a chimeric vaccine strain to protect against both types, in this study, a chimeric porcine reproductive and respiratory syndrome virus (PRRSV) type I and II was rescued using reverse genetics for the first time. Four chimeric infectious clones were designed based on the genomic arrangement of the structural proteins. However, only the clone carrying the transcriptional regulatory sequence (TRS) and ORF6 of a PRRSV-I and ORF6 of a PRRSV-II generated a viable recombinant virus, suggesting that concurrent expression of ORF6 from both parental viruses is essential for the recovery of type I and II chimeric PRRSV. The chimeric virus showed significantly lower replication ability than its parental strains in vitro, which was improved by serial passaging. In vivo, groups of pigs were inoculated with either the chimeric virus, one of the parental strains, or PBS. The chimeric virus replicated in pig tissue and was detected in serum 7 days post-inoculation. Serum neutralization tests indicated that pigs inoculated with the chimeric virus elicited neutralizing antibodies that inhibited infection with strains of both species and with greater coverage than the parental viruses. In conclusion, the application of this technique to construct a chimeric PRRSV holds promise for the development of a highly effective modified live vaccine candidate. This is particularly significant since there are currently no approved commercial divalent vaccines available to combat PRRSV-I and II co-infections.

Molecular Characterization of Porcine Reproductive and Respiratory Syndrome Virus in Korea from 2018 to 2022.

Porcine reproductive and respiratory syndrome (PRRS) is an endemic disease in the Republic of Korea. Surveillance of PRRS virus (PRRSV) types is critical to tailor control measures. This study collected 5062 serum and tissue samples between 2018 and 2022. Open reading frame 5 (ORF5) sequences suggest that subgroup A (42%) was predominant, followed by lineage 1 (21%), lineage 5 (14%), lineage Korea C (LKC) (9%), lineage Korea B (LKB) (6%), and subtype 1C (5%). Highly virulent lineages 1 (NADC30/34/MN184) and 8 were also detected. These viruses typically mutate or recombine with other viruses. ORF5 and non-structural protein 2 (NSP2) deletion patterns were less variable in the PRRSV-1. Several strains belonging to PRRSV-2 showed differences in NSP2 deletion and ORF5 sequences. Similar vaccine-like isolates to the PRRSV-1 subtype 1C and PRRSV-2 lineage 5 were also found. The virus is evolving independently in the field and has eluded vaccine protection. The current vaccine that is used in Korea offers only modest or limited heterologous protection. Ongoing surveillance to identify the current virus strain in circulation is necessary to design a vaccine. A systemic immunization program with region-specific vaccinations and stringent biosecurity measures is required to reduce PRRSV infections in the Republic of Korea.

Evaluation and Determination of a Suitable Passage Number of Codon Pair Deoptimized PRRSV-1 Vaccine Candidate in Pigs.

Porcine reproductive and respiratory syndrome virus (PRRSV) is major economic problem given its effects on swine health and productivity. Therefore, we evaluated the genetic stability of a codon pair de-optimized (CPD) PRRSV, E38-ORF7 CPD, as well as the master seed passage threshold that elicited an effective immune response in pigs against heterologous virus challenge. The genetic stability and immune response of every 10th passage (out of 40) of E38-ORF7 CPD was analyzed through whole genome sequencing and inoculation in 3-week-old pigs. E38-ORF7 CPD passages were limited to 20 based on the full-length mutation analysis and animal test results. After 20 passages, the virus could not induce antibodies to provide effective immunity and mutations accumulated in the gene, which differed from the CPD gene, presenting a reason for low infectivity. Conclusively, the optimal passage number of E38-ORF7 CPD is 20. As a vaccine, this may help overcome the highly diverse PRRSV infection with substantially enhanced genetic stability.

Codon Pair Deoptimization (CPD)-Attenuated PRRSV-1 Vaccination Exhibit Immunity to Virulent PRRSV Challenge in Pigs.

Commercially used porcine respiratory and reproductive syndrome (PRRS) modified live virus (MLV) vaccines provide limited protection with heterologous viruses, can revert back to a virulent form and they tend to recombine with circulating wild-type strains. Codon pair deoptimization (CPD) is an advanced method to attenuate a virus that overcomes the disadvantages of MLV vaccines and is effective in various virus vaccine models. The CPD vaccine against PRRSV-2 was successfully tested in our previous study. The co-existence of PRRSV-1 and -2 in the same herd demands protective immunity against both viruses. In this study, live attenuated PRRSV-1 was constructed by recoding 22 base pairs in the ORF7 gene of the E38 strain. The efficacy and safety of the CPD live attenuated vaccine E38-ORF7 CPD to protect against virulent PRRSV-1 were evaluated. Viral load, and respiratory and lung lesion scores were significantly reduced in animals vaccinated with E38-ORF7 CPD. Vaccinated animals were seropositive by 14 days post-vaccination with an increased level of interferon-γ secreting cells. In conclusion, the codon-pair-deoptimized vaccine was easily attenuated and displayed protective immunity against virulent heterologous PRRSV-1.

Application of codon pair deoptimization for ORF7-induced attenuation of type I porcine reproductive and respiratory syndrome virus without reduced immune responses.

Codon pair deoptimization (CPD) attenuated type I porcine reproductive and respiratory syndrome virus (PRRSV). Infectious clones covering the full genome of a Korean type I PRRSV (E38) were synthesized, and CPD induced nine synonymous mutants of NSP1 (n = 1) and ORF7 (n = 8). In a trial to rescue live viruses from infectious clones, only four clones with mutations at nt 177 downstream of ORF7 were rescued, which showed a substantial decrease in cellular replication ability. The rescue-failed clones had two common mutation sites with a high minimum free energy and significantly modified RNA secondary structure relative to the original virus. In infected pigs, CPD viruses demonstrated significantly lower replication ability and pathogenicity than the original virus. However, immune response level induced by the attenuated viruses and the original virus was similar. This is the first study to demonstrate that type I PRRSV virulence can be attenuated through CPD application to ORF7.

Porcine Circovirus (PCV) Genotype 2d-Based Virus-like Particles (VLPs) Induced Broad Cross-Neutralizing Antibodies against Diverse Genotypes and Provided Protection in Dual-Challenge Infection of a PCV2d Virus and a Type 1 Porcine Reproductive and Respiratory Syndrome Virus (PRRSV).

As PCV2d infection has been continuously reported in swine farms in which pigs were vaccinated with PCV2a- or 2d-based vaccines, we attempted to develop a novel vaccine using a PCV2d-based capsid to enhance its protective efficacy. In this study, recombinant virus-like particles (VLPs) of rPCV2a, rPCV2b and rPCV2d were synthesized from the capsid proteins of PCV2a, PCV2b and PCV2d field isolates, respectively. A cross-neutralization assay between the VLPs induced antisera and the field isolates demonstrated the broad cross-neutralizing activities of the rPCV2d-induced antisera. Then, the protective efficacy of rPCV2d as a vaccine candidate was investigated in commercial pigs by rPCV2d vaccination and a single- or dual-challenge infection using a PCV2d strain and a type 1 PRRSV strain. High levels of anti-PCV2d IgG and neutralizing antibodies were induced 3 weeks after vaccination. After the challenge infection, the average ADWG values of the vaccinated group were higher than those of the unvaccinated group. None or a significantly low amount of (p < 0.05) reduced PCV2 genomic DNA was found in the blood, saliva and tissues of the vaccinated pigs, when compared to the unvaccinated group. Moreover, macroscopic and microscopic lesions in the tissues were significantly (p < 0.05) reduced in the vaccinated groups. This study therefore suggests that rPCV2d may be highly useful for the control of diverse field genotypes.

Intradermal co-inoculation of codon pair deoptimization (CPD)-attenuated chimeric porcine reproductive and respiratory syndrome virus (PRRSV) with Toll like receptor (TLR) agonists enhanced the protective effects in pigs against heterologous challenge.

The objective of this study was to assess protective efficacy of vaccination using CPD-attenuated chimeric PRRSV and Toll like receptor (TLR) agonists (HSP70 c-terminal domain and HSPX) as adjuvants through different inoculation routes. In this study, a chimeric PRRSV composed of two field isolates was synthesized and attenuated by CPD in NSP1 as described in the previous study. The infection of the CPD-attenuated chimeric PRRSV to pigs of 3 weeks-old showed no clinical signs without pathological lesions in necropsy, while it induced improved cross immunity between its parent strains. The TLR agonists were expressed in E. coli and purified to be used. In challenge experiment, pigs of 3 weeks-old were vaccinated using the CPD-attenuated chimeric virus with the prepared TLR agonists through intramuscular or intradermal route, following heterologous challenge after 4 weeks of vaccination. In results, intramuscular or intradermal inoculation of the CPD-attenuated chimeric virus demonstrated excellent protective efficacy against heterologous challenges. Importantly, intradermal inoculation with the TLR agonists enhanced protective effects as shown in the significantly increased level of PRRSV-specific IFN-γ-SCs and cytokines in sera, and the significant reduction of pathological lesion and viral load in lung. This study suggested that the intradermal inoculation of CPD-attenuated chimeric PRRSV plus TLR agonists should be more effective for protection of pigs against diverse PRRS field viruses.

Efficient protection against Asia1 type foot-and-mouth disease using a chimeric vaccine strain suitable for East Asia.

The type Asia1 genetic group(G)-V lineage foot-and-mouth disease (FMD) virus was identified in the East-Asian region in 2009. To date, only Shamir has been used as a standard vaccine strain worldwide for type Asia1. To prevent type Asia1 FMD in eastern Asia, two vaccine strains (ASM-R: G-V and ASM-SM: G-V/Shamir fusion) were developed and tested against type Asia1 virus strains. After immunization with the two experimental vaccines, the ASM-SM strain showed a higher level of protection against Shamir virus in mice. Additional immunogenicity tests were carried out in cattle and pigs, revealing sufficient antibody production capable of protecting the animals against the viral challenge. In cattle, the immune response started just 2 weeks after vaccination. Immunogenicity was lower in pigs, but antibody production was greatly increased to a high level after a second vaccination round. In particular, herein, 60 % and 100 % of the vaccinated pigs challenged with the Asia1 Shamir virus were determined to be clinically protected after one and two vaccination rounds with ASM-R, respectively. Pigs vaccinated twice produced sufficient antibody titers with low virus shedding for short time. Moreover, ASM-SM single-vaccinated pigs showed 100 % protection when challenged with the Asia1 Shamir virus. In summary, the vaccine strain ASM-SM designed for the defense of the Asian region efficiently granted protection to pigs against the typical Asia1 virus, Shamir.

Improved immune responses and safety of foot-and-mouth disease vaccine containing immunostimulating components in pigs.

BACKGROUND: The quality of a vaccine depends strongly on the effects of the adjuvants applied simultaneously with the antigen in the vaccine. The adjuvants enhance the protective effect of the vaccine against a viral challenge. Conversely, oil-type adjuvants leave oil residue inside the bodies of the injected animals that can produce a local reaction in the muscle. The long-term immunogenicity of mice after vaccination was examined. ISA206 or ISA15 oil adjuvants maintained the best immunity, protective capability, and safety among the oil adjuvants in the experimental group. OBJECTIVES: This study screened the adjuvant composites aimed at enhancing foot-and-mouth disease (FMD) immunity. The C-type lectin or toll-like receptor (TLR) agonist showed the most improved protection rate. METHODS: Experimental vaccines were fabricated by mixing various known oil adjuvants and composites that can act as immunogenic adjuvants (gel, saponin, and other components) and examined the enhancement effect on the vaccine. RESULTS: The water in oil (W/O) and water in oil in water (W/O/W) adjuvants showed better immune effects than the oil in water (O/W) adjuvants, which have a small volume of oil component. The W/O type left the largest amount of oil residue, followed by W/O/W and O/W types. In the mouse model, intramuscular inoculation showed a better protection rate than subcutaneous inoculation. Moreover, the protective effect was particularly weak in the case of inoculation in fatty tissue. The initial immune reaction and persistence of long-term immunity were also confirmed in an immune reaction on pigs. CONCLUSIONS: The new experimental vaccine with immunostimulants produces improved immune responses and safety in pigs than general oil-adjuvanted vaccines.

Genetic diversity and different cross-neutralization capability of porcine circovirus type 2 isolates recently circulating in South Korea.

BACKGROUND: Porcine circovirus type 2 (PCV2) is a small single-stranded DNA virus and a primary cause of PCV-associated diseases (PCVAD) that result insubstantial economic loss for swine farms. Between 2016 and 2018, PCV2 field viruses were isolated from PCVAD-affected swine farms in South Korea and investigated for genetic and antigenic heterogeneity. RESULTS: The genetic analysis of ORF2 showed that the genotype of the Korean PCV2 field isolates has been rapidly shifted from PCV2a or 2b to mutant PCV2b known as PCV2d with 82.6 to 100% amino acid sequence similarity. PCV2-specific monoclonal antibodies (mAbs) demonstrated variable antigen-binding activity to four representative Korean PCV2 field isolates [QIA215 (PCV2a), QIA418 (PCV2b), QIA169 (PCV2d), and QIA244 (PCV2d)] without genotype specificity, and one mAb showed neutralization activity to QIA215. In a cross-virus neutralization assay using anti-PCV2 sera of pigs and guinea pigs injected with a commercial vaccine and the Korean PCV2 field isolates, the anti-porcine sera of a commercial vaccine had high neutralization activity against QIA215 and QIA418 with statistically lower activity against PCV2d viruses. Anti-guinea pig sera of QIA215, QIA418, QIA169, and a commercial vaccine had high neutralization activity against all of the viruses with significantly lower activity against QIA244. Importantly, anti-guinea pig sera of QIA244 had high neutralization activity against all of the viruses. CONCLUSIONS: This study confirmed genetic and antigenic diversity among recent PCV2 field isolates in Korean swine farms, and the strain-based difference in virus neutralization capability should be considered for more effective control by vaccination.

Antigenic properties of a novel vaccine strain for type Asia1 foot-and-mouth disease in pigs.

Newly developed vaccine strains to prevent foot-and-mouth disease caused by the emerging serotype Asia1 virus were evaluated. To protect against the group (G)-VIII strain, which occurred recently, we produced an infectious cDNA clone of Asia1 Shamir cDNA (Asia1 Shamir-R). In addition, by adding a site 1 epitope of VP1 of the G-VIII lineage virus to this virus, we produced a new virus (Sham GVIII- EPI), and another virus(Sham GVIII-VP1) was replaced with that of G-VIII lineage in the VP1 region of Shamir. Test vaccines were produced using these three types of vaccine virus, and their immunogenicity and protection capabilities were evaluated in mice. Immunized mice were challenged with the Asia1 Shamir or G-VIII virus, and the results show that all the vaccines have similar protective effects. As they showed similar antigenicity, we chose the Shamir-R vaccine. Pigs maintained relatively high neutralizing antibody levels against homologous viruses of the Shamir and G-VII or G-VIII lineage three to four weeks after immunization. However, they formed relatively low levels of antibodies to G-IV and G-V viruses. In conclusion, we produced a vaccine candidate capable of protection against the G-VIII virus in the vaccine experiment for the type Asia1 serotype vaccine. This Shamir-R vaccine virus was found to protect against the viruses of the Asia1 genotype G-VII and G-VIII lineages, which occurred recently in Asia.

Field porcine reproductive and respiratory syndrome viruses (PRRSV) attenuated by codon pair deoptimization (CPD) in NSP1 protected pigs from heterologous challenge.

Two type 2 field porcine reproductive and respiratory syndrome viruses (PRRSV) isolated from PRRS-affected swine farms were attenuated by de-optimization of codon pair bias in NSP1. In 3-week-old pigs infection, the attenuated viruses showed significantly lower replication ability than the original viruses without distinct clinical sign and pathological lesions, which were observed in pig infected with the original viruses. Regarding induction of PRRSV specific immunity, the level of the neutralizing antibodies as well as secretion of IFN-γ-SCs in PBMCs was not different between the attenuated viruses and the original viruses. More importantly, pigs infected with the attenuated viruses exhibited significant reduction in respiratory scores, viremia, macroscopic and microscopic lung lesion scores, and PRRSV-antigen with interstitial pneumonia against a heterologous challenge with a type 2 virulent strain. Conclusively, the viruses attenuated by CPD in this study demonstrated potential usefulness as vaccine strains to provide protective immunity against diverse virulent PRRSVs.

Improved foot-and-mouth disease vaccine with O PanAsia-2 strain protect pigs against O/Jincheon/SKR/2014 originated from South Korea.

Efforts are required to develop foot-and-mouth disease (FMD) vaccines in Asia that can respond to the type O outbreaks that have continued with the devastating damage since 2010. It is necessary to develop vaccine strains that can provide protection against the ME-SA topotype, which has tended to spread into neighboring areas, and the frequent SEA topotype outbreaks. To this end, this study aimed to develop a FMD vaccine utilizing O PanAsia-2 that is able to provide broad protection against ME-SA as the vaccine strain, with a focus on the O/Jincheon/SKR/2014 virus (SEA topotype), the outbreaks of which have persisted in spite of the enforcement of FMD vaccination. The virus neutralizing antibody (VN) titer to the ME-SA topotype (especially, Ind2001 lineage) virus in pigs was the highest, followed by SEA, while the VN titers to the Cathay and EURO-SA topotypes were similar. In the O/Jincheon/SKR/2014 virus challenge test, all pigs were protected against the virus, and almost no virus shedding was detected after the virus challenge. In the immunization test performed on cattle and pigs, antibodies with sufficient protective activity were produced in cattle two weeks after the first immunization, and pigs exhibited lower immunity compared to cattle. However, immunity was improved enough in pigs to provide protection against the virus challenge after the second immunization, with a significant increase in antibody production.

Evaluation of novel inactivated vaccines for the SAT 1, SAT 2 and SAT 3 serotypes of foot-and-mouth disease in pigs.

BACKGROUND: The foot-and-mouth disease (FMD) virus is classified into seven serotypes, of which the South African types have South African Territories (SAT)1, SAT2, and SAT3 that are prevalent in Africa. Especially SAT2 have spread to Arabian Peninsula and the Palestinian Autonomous Territories. Of these viruses, the incidence of SAT2 is the highest. It is important to prepare for the spread of the virus to other continents, even though most FMD viruses are bovine-derived. In particular, due to the high breeding density of pigs in Asia, more attention is usually paid to the immunity and protection of pigs than cattle. For this reason, this study investigated the immunity and protection of pigs against the SAT viruses. METHODS: Specific vaccines were developed for SAT1, SAT2, and SAT3 serotypes. These vaccine viruses were designed to be distinguished from the wild-type strain. An immunogenicity test was conducted using these vaccines in both cattle (n = 5/group) and pigs (n = 20/group). RESULTS: High virus-neutralizing titer of antibodies (> 1:100) was induced in only 2 weeks after the immunization of cattle with the individual vaccine for SAT1, SAT2 or SAT3, and a clear immune response was induced after the second immunization in pigs. When the vaccinated pigs (n = 4-5/group) were challenged by the homologous wild-type virus strain 4 weeks after immunization, all the pigs were protected from the challenge. CONCLUSIONS: This study confirmed that these vaccines can be used against SAT1, SAT2, and SAT3 viruses in cattle and pigs. The vaccine strains developed in this study are expected to be used as vaccines that can protect against FMD in the event of a future FMD outbreak in pigs in consideration of the situation in Asia.

Improved foot-and-mouth disease vaccine, O TWN-R, protects pigs against SEA topotype virus occurred in South Korea.

Foot-and-mouth disease (FMD) is a highly contagious disease and causes economic damage at a national level. In particular, the type O FMD virus (FMDV) is a serotype that causes FMD outbreaks most frequently in the world. In recent years, Southeast Asia (SEA), Middle East-South Asia (ME-SA), and Cathay topotype-mediated FMD are prevalent in Asia, among which the SEA and ME-SA topotypes cause a majority of the outbreaks. The SEA topotype virus is more likely to infect both cattle and pigs simultaneously, thereby resulting in more severe damages; thus, it is necessary to study the protection ability of the candidate vaccines of this topotype after immunization. In this study, an experimental vaccine for pigs was produced using a vaccine strain that contains the structural protein of the O Taiwan97 strain, which was derived from the Cathay topotype, and its effect was evaluated. In the immunization test in pigs and cattle, the antibody titers were found to be elevated two weeks after immunization and very high titers of neutralizing antibodies were formed after four weeks. After the second inoculation, very high titers of neutralizing antibodies were produced in both species in the fourth week after immunization, and the antibodies maintained for up to six months and three months in cattle and pigs, respectively. No significant immunological difference in antibody production was observed in cattle and pigs. This study confirmed that complete protection from the challenge of the SEA topotype virus (O/Jincheon/SKR/2014), although the antibody titers against O/Jincheon/SKR/2014 strain were not that high, was achieved through immunization with the newly developed Cathay topotype vaccine in pigs.

New foot-and-mouth disease vaccine, O JC-R, induce complete protection to pigs against SEA topotype viruses occurred in South Korea, 2014-2015.

Foot-and-mouth disease (FMD) is an acute epidemic that spreads rapidly among cattle and pigs. In 2014, in Korea, despite enforced vaccination, the type O Southeast Asia (SEA) topotype viruses (Mya-98 lineage) infected mainly cattle and pigs simultaneously, thereby causing enormous damage. If a vaccine that is completely protective against this FMD virus is developed and used, it can become a very important preventive measure in Asia, which is where this type of virus mainly circulates. The SEA topotype has been steadily evolving and transforming into new variations since it became epidemic in Asia. Therefore, it became necessary to develop a new vaccine that could provide protection against the FMD virus strain that was responsible for the 2014-2015 outbreak in Korea. This study aimed to develop a vaccine that would provide complete protection against the SEA topotype FMD virus to control sporadic FMD outbreaks, which occur despite the enforcement of vaccination, and to completely prevent virus shedding, thereby preventing the virus from spreading. The vaccine candidate virus developed in this study showed low pathogenicity and can be distinguished from the wild-type FMD virus strain. The developed vaccine was able to protect mice from SEA and Middle East-South Asia topotype virus strains and induced high titers of antibodies against both virus strains in pigs, thereby confirming the sufficiency of its protective function. In particular, the results of the SEA topotype virus challenge test in pigs revealed that perfect immunity was created in the vaccinated pigs, without virus shedding and viremia.

Evaluation of novel inactivated vaccine for type C foot-and-mouth disease in cattle and pigs.

Foot-and-mouth disease virus (FMDV) is the cause of an economically devastating disease in major cloven-hoofed livestock. Although type C foot-and-mouth disease (FMD) has not occurred anywhere worldwide since 2004, the antigen bank should be preserved in preparation for an unexpected outbreak. We therefore conducted experiments to develop inactivated vaccines that are safer and exhibit improved characteristics over existing vaccines. Our previous study showed that the replacement of the capsid-encoding gene (P1) from the vaccine strain O1 Manisa could be rescued successfully from the vaccine strains. In addition, novel point mutation in the 3C region in the virus genome, for induction of properties with low pathogenesis to create a safe vaccine, and 3B1B2 replacement, for differential diagnosis with the wild type virus, were performed. The modified FMD vaccine strain, C3 Resende-R, was shown to provide lower pathogenesis in young mice than the wild-type virus. To identify the immune responses after vaccination with 146S antigen (15 µg/mL/dose), we conducted a virus neutralization test using serum from pigs and cattle vaccinated with the inactivated vaccine. The neutralizing titers in the cattle were higher than those in the pigs and maintained mean antibody titers of around 1:100 until the end of the experiment. The vaccine showed protection capability of 16 PD50 against C3 Resende virus in the pigs. The replacement of the structural protein-coding gene for the new FMDV was a useful tool in the development of an effective vaccine candidate strain. This inactivated vaccine will be used for the establishment of a safe vaccine strain for the antigen bank.

Chimeric vaccine strain of type O foot-and-mouth disease elicits a strong immune response in pigs against ME-SA and SEA topotypes.

Foot-and-mouth disease (FMD) is an acute infectious disease occurring in cloven-hoofed animals. There are many variations of the virus, making it difficult to protect against the various strains with one virus vaccine. The immunogenicity has generally been evaluated in pigs using neutralizing antibodies to determine the protection level against foot-and-mouth disease virus type O. Therefore, the vaccine from the chimeric vaccine strain of ME-SA (VP4, VP2, and VP3) and SEA (VP1) topotypes developed in this study is expected to be able to protect with high neutralizing antibody titers against most of the eight FMD viruses of the four different topotypes (ME-SA, SEA, Cathay, and EURO-SA) of type O in pigs. This is a new technique for powerful vaccine development, with multiple preventive roles against various epidemic FMD strains.