A simple colorimetric detection of porcine epidemic diarrhea virus by reverse transcription loop-mediated isothermal amplification assay using hydroxynaphthol blue metal indicator.

A simple reverse transcription loop-mediated isothermal amplification combined with visual detection method (vRT-LAMP) assay was developed for rapid and specific detection of porcine epidemic diarrhea virus (PEDV) in this study, which overcomes the shortcomings of previously described RT-LAMP assays that require additional detection steps or pose a risk of cross-contamination. The assay results can be directly detected by the naked eye using hydroxynaphthol blue after incubating for 40 min at 62 °C. The assay specifically amplified PEDV RNA and no other viral nucleic acids.

Probe-based real-time reverse transcription loop-mediated isothermal amplification (RRT-LAMP) assay for rapid and specific detection of foot-and-mouth disease virus.

Rapid and specific detection of foot-and-mouth disease virus (FMDV) is a key factor for promoting prompt control of FMD outbreaks. In this study, a real-time reverse transcription loop-mediated isothermal amplification (RRT-LAMP) assay with high sensitivity, rapidity and reliability was developed using a targeted gene-specific assimilating probe for real-time detection of seven FMDV serotypes. Positive assay signals were generated within 15 min for the lowest concentration of a standard RNA sample at 62°C; this was substantially faster than that achieved by the OIE (World Organisation for Animal Health)-recommended real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) assay.

Genomic characterization of classical swine fever virus LOM variants with 3'-UTR INDELs from pigs on Jeju Island, South Korea.

Classical swine fever virus (CSFV) reemerged in naïve pig herds on Jeju Island, South Korea, due to the accidental introduction of the LOM vaccine strain in 2014. Since this reemergence, the previously CSFV-free region has experienced numerous outbreaks, causing the virus to become endemic in provincial herds. In this study, we determined the complete genome sequences and investigated the molecular characteristics of LOM-derived field CSFV strains with unique insertion-deletion (INDEL) mutations in the 3'-untranslated region (UTR) that were responsible for ongoing sporadic outbreaks on Jeju Island in 2019.

Genomic characteristics and pathogenicity of natural recombinant porcine reproductive and respiratory syndrome virus 2 harboring genes of a Korean field strain and VR-2332-like strain.

Porcine reproductive and respiratory syndrome (PRRS), an economically-important disease caused by PRRS virus (PRRSV), has become endemic to most pig-producing countries. Point mutation and recombination are responsible for genetic heterogeneity, resulting in circulation of genetically-diverse strains. However, no natural recombinant PRRSV has yet been identified in Korea.

Endemic outbreaks due to the re-emergence of classical swine fever after accidental introduction of modified live LOM vaccine on Jeju Island, South Korea.

After the unintentional vaccination of the LOM vaccine strain in 2014, classical swine fever virus (CSFV) reemerged in naïve pig herds on Jeju Island, South Korea, which had been a CSF-free region with a non-vaccination policy for a decade. Since the re-emergence, endemic outbreaks of CSFV have occurred in the island, causing enormous damage to provincial pig farms. The present study reports the complete genome sequences and molecular characterization of the LOM-derived field CSFV strains responsible for the current outbreaks on Jeju Island.

Differential evolution of antigenic regions of porcine reproductive and respiratory syndrome virus 1 before and after vaccine introduction.

Porcine reproductive and respiratory syndrome virus (PRRSV) is a widespread viral pathogen that has caused tremendous economic losses throughout most pig-producing countries. Nowadays, both PRRSV-1 and PRRSV-2 co-circulate in Korean pig populations, and commercial modified live vaccine (MLV) is predominantly used to control PRRS. Specifically, control strategy using only PRRSV-2 MLV that was used since 1995 cannot prevent the spread of PRRSV-1 and damage from its infection, which led to the first introduction of two additional PRRSV-1 vaccines in 2014.

Independent evolution of porcine reproductive and respiratory syndrome virus 2 with genetic heterogeneity in antigenic regions of structural proteins in Korea.

Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically important pathogen that affects the global swine industry. The continuous evolution of this virus has made control and prevention difficult, which emphasizes the importance of monitoring currently circulating PRRSV strains. In this study, we investigated the genetic characteristics of whole structural genes of 35 PRRSV-2 isolates that circulated between 2012 and 2017 in Korea.

Synergistic effect of ribavirin and vaccine for protection during early infection stage of foot-and-mouth disease.

In many countries, vaccines are used for the prevention of foot-and-mouth disease (FMD). However, because there is no protection against FMD immediately after vaccination, research and development on antiviral agents is being conducted to induce protection until immunological competence is produced. This study tested whether well-known chemicals used as RNA virus treatment agents had inhibitory effects on FMD viruses (FMDVs) and demonstrated that ribavirin showed antiviral effects against FMDV .

Genetic identification and serological evaluation of commercial inactivated foot-and-mouth disease virus vaccine in pigs.

Vaccination is considered a frequently used tool to prevent and control foot-and-mouth disease (FMD). However, the effectiveness of conventional FMD virus (FMDV) vaccines in pigs has been controversial because the massive prophylactic vaccination could not elicit proper immune response nor prevent the broad spread of FMD outbreak, mainly in pig farms, in South Korea during outbreaks of 2014. In addition, there has been little information on the efficacy of inactivated, high potency, multivalent, oil-based FMDV vaccine in pigs, because an evaluation of FMDV vaccines had been mainly carried out using cattle.

Detection and genetic characterization of porcine circovirus 3 from aborted fetuses and pigs with respiratory disease in Korea.

A novel porcine circovirus 3 (PCV3) was first detected in pigs showing porcine dermatitis and nephropathy syndrome, reproductive failure, and multisystemic inflammation in the USA. Herein, we report on PCV3 as a potential etiological agent of clinical signs, reproductive failure and respiratory distress on Korean pig farms, based on hybridization, pathological, and molecular findings. Confirmation of the presence of PCV3 may increase co-infection with other causative agents of disease in Korean pig herds, indicating the need for further systemic investigation of pathogenicity and of multiple infections with PCV2 genotypes and bacteria, and the development of an effective PCV3 vaccine.

Classical Swine Fever Outbreak after Modified Live LOM Strain Vaccination in Naive Pigs, South Korea.

We report classical swine fever outbreaks occurring in naive pig herds on Jeju Island, South Korea, after the introduction of the LOM vaccine strain. Two isolates from sick pigs had >99% identity with the vaccine stain. LOM strain does not appear safe; its use in the vaccine should be reconsidered.

Complete Genomic Characterization of Korean Porcine Epidemic Diarrhea Virus Strain KUPE21.

Nationwide porcine epidemic diarrhea virus (PEDV) outbreaks occurred in late 2013 in the Republic of Korea, resulting in an expansion of genomic data for Korean PEDVs. However, the data available for Korean PEDVs before 2013 are insufficient. Therefore, we sequenced and analyzed the complete genome of a Korean PEDV strain, KUPE21, which was isolated in the early 2000s.

Challenges of influenza A viruses in humans and animals and current animal vaccines as an effective control measure.

Influenza A viruses (IAVs) are genetically diverse and variable pathogens that share various hosts including human, swine, and domestic poultry. Interspecies and intercontinental viral spreads make the ecology of IAV more complex. Beside endemic IAV infections, human has been exposed to pandemic and zoonotic threats from avian and swine influenza viruses.

Loop-mediated isothermal amplification assay for the rapid and visual detection of novel porcine circovirus 3.

A loop-mediated isothermal amplification (LAMP) assay using hydroxynaphthol blue was developed for the rapid and visual detection of the capsid gene of porcine circovirus 3 (PCV3). The amplification could be completed in 40 min at 62°C, and the results could be visually detected by the naked eye. The assay specifically amplified PCV3 DNA and not other porcine viral nucleic acids.

Multiplex real-time polymerase chain reaction for the differential detection of porcine circovirus 2 and 3.

A multiplex quantitative real-time polymerase chain reaction (mqPCR) assay was developed for the rapid and differential detection of porcine circovirus 2 (PCV2) and PCV3. Each of the capsid genes of PCV2 and PCV3 were amplified using specific primers and probe sets, while no other porcine pathogen genes were detected. Limit of detection of the assay was below 50 copies of the target genes of PCV2 and PCV3, and was comparable to that of previously described methods The assay showed high repeatability and reproducibility, with coefficients of intra-assay and inter-assay variation of less than 4.

Prevalence of novel porcine circovirus 3 in Korean pig populations.

Porcine circovirus 3 (PCV3) is a novel porcine circovirus that was identified in pigs with porcine dermatitis and nephropathy syndrome, reproductive failure, and multi-systemic inflammation. However, the distribution and genetic characteristics of emerging PCV3 in Korea remains unclear. In this study, we determined the nationwide prevalence and genetic characteristics of PCV3 using pen-based oral fluid samples.

Genetic diversity of ORF 4-6 of type 1 porcine reproductive and respiratory syndrome virus in naturally infected pigs.

Genotype 1 porcine reproductive and respiratory syndrome virus (PRRSV) has been highly prevalent throughout Korea since the virus was first detected in 2005. However, genetic analyses of genotype 1 PRRSV in Korea have been limited to ORF5 and/or ORF7. In the present study, we determined 10 representative sequence covering ORF4 to ORF6 and each individual ORFs of genotype 1 PRRSV in Korea, and performed molecular analyses.

Challenges of Generating and Maintaining Protective Vaccine-Induced Immune Responses for Foot-and-Mouth Disease Virus in Pigs.

Vaccination can play a central role in the control of outbreaks of foot-and-mouth disease (FMD) by reducing both the impact of clinical disease and the extent of virus transmission between susceptible animals. Recent incursions of exotic FMD virus lineages into several East Asian countries have highlighted the difficulties of generating and maintaining an adequate immune response in vaccinated pigs. Factors that impact vaccine performance include (i) the potency, antigenic payload, and formulation of a vaccine; (ii) the antigenic match between the vaccine and the heterologous circulating field strain; and (iii) the regime (timing, frequency, and herd-level coverage) used to administer the vaccine.

Genotypic diversity of porcine circovirus type 2 (PCV2) and genotype shift to PCV2d in Korean pig population.

Porcine circovirus type 2 (PCV2) is a causative agent of PCV2-associated disease (PCVAD), which leads to enormous economic losses in the swine industry worldwide. A high nucleotide substitution rate allows for the continuous evolution of PCV2 and the emergence of novel PCV2 strains. However, the distribution of emerging PCV2 genotypes and the co-existence of multiple genotypes in Korea have not been elucidated.