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Clostridium perfringens constitutes the normal gut microbiome in pigs; however, it can potentially cause pre- and post-weaning diarrhea. Nevertheless, the importance of this bacterium as a primary pathogen of diarrhea in piglets needs to be better understand, and the epidemiology of C. perfringens in Korean pig populations is unknown. To study the prevalence and typing of C. perfringens, 203 fecal samples were collected from diarrheal piglets in 61 swine farms during 2021–2022 and examined for the presence of C. perfringens and enteric viruses, including porcine epidemic diarrhea virus (PEDV). We determined that the most frequently identified type of C. perfringens was C. perfringens type A (CPA; 31.5%). Among them, the single-infection of CPA (46.9%) and co-infection of CPA with PEDV (45.3%) were most common in diarrheal samples. Furthermore, we conducted animal experiments to investigate the clinical outcomes of single- and co-infections of highly pathogenic (HP)-PEDV and CPA in weaned piglets. Our results illustrated that the pigs infected with HP-PEDV or CPA showed no or mild diarrhea without mortality. However, the animals co-inoculated with HP-PEDV and CPA underwent more severe diarrheal symptoms when compared to those of the single-infection pigs. Additionally, CPA promoted PEDV replication in co-infected piglets with evidence of high viral titers in the feces. A histopathological examination revealed more severe villous atrophy in the small intestine of co-infected pigs than in single-infection pigs. There were obvious synergistic clinical implications between PEDV and CPA co-infection in weaned piglets.

Highlights • Attenuated G2b PEDV strain S DEL5/ORF3 was pioneered to develop an MLV vaccine. • S DEL5/ORF3 did not revert to virulence after successive back passages in piglets. • Prime-boost maternal vaccinations conferred complete protection against PEDV. • Robust humoral immunity was observed in the sera and colostrum of vaccinated dams. • Sufficient lactogenic immunity provides passive protection in suckling neonates., We have previously reported the generation of the attenuated KNU-141112-S DEL5/ORF3 virus by continuous propagation of highly virulent G2b porcine epidemic diarrhea virus (PEDV) in Vero cells. The present study aimed to assess the safety of S DEL5/ORF3 and to evaluate its effectiveness as a live vaccine for prime-booster vaccinations. Reversion to virulence experiments revealed that the S DEL5/ORF3 strain retains its attenuated phenotype and genetic stability after five successive passages in susceptible piglets. Pregnant sows were primed orally with an S DEL5/ORF3 live vaccine and boosted intramuscularly twice with a commercial killed vaccine at 2-week intervals prior to parturition. This sow vaccination regimen completely protected nursing piglets against virulent G2b challenge, as evidenced by the increase in survival rate from 0% to 100% and the significant reduction in diarrhea intensity, including the amount and duration of PEDV fecal shedding. In addition, despite a 2–3 day period of weight loss in piglets from vaccinated sows after challenge, their daily weight gain was recovered at 7 days post-challenge and became similar to that of unchallenged pigs from unvaccinated sows over the course of the experiment. Furthermore, strong antibody responses to PEDV were verified in the sera and colostrum of immunized sows with the prime-boost treatment and their offspring. Altogether, our data demonstrated that the attenuated S DEL5/ORF3 strain guarantees the safety to host animals with no reversion to virulence and is suitable as an effective primary live vaccine providing durable maternal lactogenic immunity for passive piglet protection.

Porcine epidemic diarrhea (PED) is a devastating disease that causes considerable economic damage to the global pig industry. Although the causative agent, the porcine epidemic diarrhea virus (PEDV), was identified about a half century ago, there is still much debate on the preventive measures against the disease, especially regarding the PED vaccine. Recent reports on PEDV variants make the vaccination for PEDV more confusing. Therefore, we systematically reviewed published articles on PED and vaccines against the disease and performed a meta-analysis of vaccine efficacy based on the clinical signs, fecal score and survival rates. A total of 299 articles on the efficacy of PED vaccines were found online, and 21 articles were selected that fulfilled all the criteria. A meta-analysis was performed on the 21 articles based on the fecal scores and survival rates. This analysis showed the efficacy of PED vaccines, and no significant differences in the efficacy depending on vaccine type (killed vs. live) or administration route (intramuscular vs. oral) were found. The results from our study suggest that any vaccination against PED is a useful strategy to control the disease regardless of the type of vaccine and administration route.

The recent emergence and re-emergence of porcine epidemic diarrhea virus (PEDV) underscore the urgent need for the development of novel, safe, and effective vaccines against the prevailing strain. In this study, we generated a cold-adapted live attenuated vaccine candidate (Aram-P29-CA) by short-term passage of a virulent PEDV isolate at successively lower temperatures in Vero cells. Whole genome sequencing identified 12 amino acid changes in the cold-adapted strain with no insertions and deletions throughout the genome. Animal inoculation experiments confirmed the attenuated phenotype of Aram-P29-CA virus in the natural host. Pregnant sows were orally administered P29-CA live vaccines two doses at 2-week intervals prior to parturition, and the newborn piglets were challenged with the parental virus. The oral homologous prime-boost vaccination of P29-CA significantly improved the survival rate of the piglets and notably mitigated the severity of diarrhea and PEDV fecal shedding after the challenge. Furthermore, strong antibody responses to PEDV were detected in the sera and colostrum of immunized sows and in the sera of their offspring. These results demonstrated that the cold-adapted attenuated virus can be used as a live vaccine in maternal vaccination strategies to provide durable lactogenic immunity and confer passive protection to litters against PEDV.

Haemophilus parasuis causes contagious porcine Glässer's disease leading to severe losses in the swine industry. In this study, we established an efficient Escherichia colibased system for the expression of H. parasuis major outer-membrane protein (MOMP) that has been known as a good vaccine candidate against Glässer's disease. Use of an E. coli-derived pelB leader sequence made it possible to produce recombinant MOMP (rMOMP) as the soluble forms without an additional refolding process. Using two different animal models, it was evaluated that the rMOMP was capable of inducing a significant immune response and providing protection against H. parasuis infection.

In Korea, the addition of antibiotics to feed was banned in July 2011; since then, reports of outbreaks of porcine pleuropneumonia have increased. Therefore, knowledge of the characteristics of clinical isolates emerging in recent years is needed. This study analysed the serotype and antimicrobial susceptibility of 102 Actinobacillus pleuropneumoniae isolates from pigs with pleuropneumonia in Korea from 2006 to 2010. Serotype 5 was the most frequently isolated but the incidence of serotype 1 significantly increased in 2010. The susceptibility to florfenicol decreased considerably from 2006 to 2010, as did that of a minor percentage of isolates to ampicillin and amoxicillin. Of 11 tetracycline resistance genes, tet (B) was predominant (62 per cent), followed by tet (H) and tet (O). The florfenicol resistance ( flo R) gene (34 per cent) and β-lactam antibiotic resistance ( bla ROB-1) gene (15 per cent) were also detected. The expression levels of the tetracycline repressor gene and resistance gene were not significantly correlated with the minimum inhibitory concentration values of tetracycline-resistant strains. Interspecies transferability of the resistance genes ( flo R, tet (B)/ bla ROB-1) was observed with frequencies of 5.7×10−3 and 3.5×10−2, respectively. In analysing DNA patterns using pulsed field gel electrophoresis, there was a slight positive correlation with serotypes but not with isolated location and year. This study acknowledges the emergence of new serotype and antimicrobial resistance of A pleuropneumoniae based on the current situation in Korea. This knowledge may be useful in controlling the disease caused by A pleuropneumoniae . Actinobacillus pleuropneumoniae is a causative agent of porcine pleuropneumonia, a respiratory disease in pigs of all ages that may result in sudden death often detected in the postmortem inspection at slaughter, or in severe symptoms characterised by fibrinous pleuritis and haemorrhagic and fibrinous pneumonia with necrotic lung lesions (Bosse and others 2002 …

This study was focusing on evaluating the protection of polyphosphate kinase (ppk) deleted and/or temperature-sensitive (ts) Salmonella Enteritidis (SE) as an attenuated vaccine in chickens. We constructed SEppk, SEts and SEppk::ts mutants and screened those mutants by growth capability in vitro, protection study in mice model and antibody response in chickens. Among the mutants, SEppk::ts-3 was selected because it showed higher growth capability, good protection against highly virulent SE in mice model, and good antibody response in chickens. SEppk::ts-3 also showed good protection against highly virulent SE isolate because it decreased colonization of virulent SE challenge strain in spleen, liver and cecum compared with the non-vaccinated control. The SEppk::ts-3 mutant showed cross- protection against S. Gallinarum (SG) challenge although the its cross-protection rate was a little lower than that of SG9R, a commercial vaccine against SG infection. To use for live attenuated vaccine in chickens, it should further be characterized.