First Detection and Genetic Characterization of Swine Orthopneumovirus from Domestic Pig Farms in the Republic of Korea

Novel swine orthopneumovirus (SOV) infections have been identified in pigs in the USA and some European countries but not in Asian countries, including South Korea, to date. The current study reports the first SOV infections in four domestic pig farms located in four provinces across South Korea. The detection rate of SOV in oral fluid samples using qRT-PCR was 4.4% (14/389), indicating the presence of the virus in pigs at commercial farms in Korea. Two complete genome sequences and one glycoprotein (G) gene sequence were obtained from SOV-positive samples. The complete genome analysis of KSOV-2201 and KSOV-2202 strains showed 98.2 and 95.4% homologies with a previously reported SOV, and the phylogenetic tree exhibited a high correlation with a previously reported SOV strain from the US and a canine pneumovirus (CPnV) strain from China. Based on the genetic analysis of the viral G gene, the murine pneumonia virus (MPV)-like orthopneumoviruses (MLOVs) were divided into two genogroups (G1 and G2). Seventeen CPnVs and two feline pneumoviruses were grouped into G1, while the Korean SOV strains identified in this study were grouped into G2 along with one SOV and two CPnVs. These results will contribute to expanding our understanding of the geographical distribution and genetic characteristics of the novel SOV in the global pig population.

An Advanced Multiplex Real-Time Reverse Transcription Loop-Mediated Isothermal Amplification Assay for Rapid and Reliable Detection of Porcine Epidemic Diarrhea Virus and Porcine Internal Positive Control

For rapid and reliable detection of porcine epidemic diarrhea virus (PEDV) from pig clinical samples, a multiplex, real-time, reverse transcription loop-mediated isothermal amplification (mqRT-LAMP) was developed using two sets of primers and assimilating probes specific to the PEDV N gene and the Sus scrofa β-actin gene, which was used as an endogenous internal positive control (EIPC) to avoid false-negative results. The assay specifically amplified both target genes of PEDV and EIPC in a single reaction without any interference but did not amplify other porcine viral nucleic acids. The limit of detection was 10 copies/μL, 100-fold lower than that of a reverse transcription-polymerase chain reaction (RT-PCR) and equivalent to that of quantitative/real-time RT-PCR (qRT-PCR). This assay has high repeatability and reproducibility with coefficients of variation < 4.0%. The positive signal of the mqRT-LAMP assay was generated within 25 min, demonstrating advantages in rapid detection of PEDV over RT-PCR or qRT-PCR assay, which require at least 2 h turnaround times. In clinical evaluation, the detection rate of PEDV by mqRT-LAMP assay (77.3%) was higher than that of RT-PCR assay (69.7%), and comparable to qRT-PCR (76.8%) with almost 100% concordance (kappa value 0.98). The developed mqRT-LAMP assay can serve as an advanced alternative method for PEDV diagnosis because it has high sensitivity and specificity, rapidity, and reliability even in resource-limited laboratories.

Identification of the O/ME-SA/Ind-2001e Sublineage of Foot-and-Mouth Disease Virus in Cambodia

Foot-and-mouth (FMD) is endemic in Cambodia with numerous outbreaks in cattle, pigs and other susceptible animal species reported every year. Historically, these outbreaks were caused by the FMD virus (FMDV) of serotype O PanAsia and Mya-98 lineages and serotype A Sea-97 lineage. However, the trans-pool movement of FMDV between inter-pool regions or countries throughout FMD endemic regions has raised concerns regarding infection with the new genotype or serotype of FMDV in Cambodia. In this study, 19 sequences of VP1 coding region obtained from 33 clinical samples collected from FMDV-affected cattle farms in Cambodia during January to March 2019 were genetically characterized to identify the genotypes/lineages of FMDV. Phylogenetic analysis of VP1 coding sequences revealed that recent field viruses belonged to O/ME-SA/Ind-2001e (15.8%), O/ME-SA/PanAsia (52.7%), and A/ASIA/Sea-97 (31.5%). Besides, the field viruses of O/ME-SA/Ind-2001e in Cambodia showed 93.5-96.8% identity with the VP1 coding sequences of the same sublineage viruses from pool 1 and 2 surrounding Cambodia. This is the first report of O/ME-SA/Ind-2001e infection in Cambodia, suggesting that the trans-pool movement of the new genotype should be closely monitored for efficient control of FMD.

Phage Display Screening of Bovine Antibodies to Foot-and-Mouth Disease Virus and Their Application in a Competitive ELISA for Serodiagnosis

For serodiagnosis of foot-and-mouth disease virus (FMDV), monoclonal antibody (MAb)-based competitive ELISA (cELISA) is commonly used since it allows simple and reproducible detection of antibody response to FMDV. However, the use of mouse-origin MAb as a detection reagent is questionable, as antibody responses to FMDV in mice may differ in epitope structure and preference from those in natural hosts such as cattle and pigs. To take advantage of natural host-derived antibodies, a phage-displayed scFv library was constructed from FMDV-immune cattle and subjected to two separate pannings against inactivated FMDV type O and A. Subsequent ELISA screening revealed high-affinity scFv antibodies specific to a serotype (O or A) as well as those with pan-serotype specificity. When BvO17, an scFv antibody specific to FMDV type O, was tested as a detection reagent in cELISA, it successfully detected FMDV type O antibodies for both serum samples from vaccinated cattle and virus-challenged pigs with even higher sensitivity than a mouse MAb-based commercial FMDV type O antibody detection kit. These results demonstrate the feasibility of using natural host-derived antibodies such as bovine scFv instead of mouse MAb in cELISA for serological detection of antibody response to FMDV in the susceptible animals.

Development of Monoclonal Antibody Specific to Foot-and-Mouth Disease Virus Type A for Serodiagnosis

Foot-and-mouth disease (FMD) is a highly contagious and economically devastating disease affecting cloven-hoofed livestock worldwide. FMD virus (FMDV) type A is one of the most common causes of FMD outbreaks among the seven FMDV serotypes, and its serological diagnosis is therefore important to confirm FMDV type A infection and to determine FMD vaccine efficacy. Here, we generated monoclonal antibodies (mAbs) specific to FMDV type A via hybridoma systems using an inactivated FMDV type A (A22/Iraq/1964) and found 4 monoclones (#29, #106, #108, and #109) with high binding reactivity to FMDV type A among 594 primary clones. In particular, the #106 mAb had a higher binding reactivity to the inactivated FMDV type A than the other mAbs and a commercial mAb. Moreover, the #106 mAb showed no cross-reactivity to inactivated FMDV type South African territories 1, 2, and 3, and low reactivity to inactivated FMDV type O (O₁ Manisa). Importantly, the solid-phase competitive ELISA (SPCE) using horseradish peroxidase (HRP)-conjugated #106 mAb detected FMDV type A-specific Abs in sera from FMD type A-vaccinated cattle more effectively than a commercial SPCE. These results suggest that the newly developed FMDV type A-specific mAb might be useful for diagnostic approaches for detecting Abs against FMDV type A.

Investigation of bovine tuberculosis outbreaks by using a trace-back system and molecular typing in Korean Hanwoo beef cattle

Bovine tuberculosis is a chronic contagious disease responsible for major agricultural economic losses. Abattoir monitoring and trace-back systems are an appropriate method to control bovine tuberculosis, particularly in beef cattle. In the present study, a trace-back system was applied to bovine tuberculosis cases in Korean native Hanwoo beef cattle. Bovine tuberculosis was detected in three index beef cattle during abattoir monitoring in Jeonbuk Province, Korea, and the original herds were traced back from each index cow. All cattle in each original herd were subjected to tuberculin skin test. The positive rates in the tuberculin skin test were 64.6% (62 of 96), 4.8% (2 of 42), and 8.1% (3 of 37) at farms A, B, and C, respectively. On post-mortem examination of 56 tuberculin-positive cattle, 62% had granulomatous lesions, and Mycobacterium bovis was cultured from 40 (71.4%) of the cattle. Molecular typing by spoligotyping and the mycobacterial interspersed repetitive unit-variable-number tandem repeat assay revealed the genotype of the M. bovis strains from the index cattle were same as the M. bovis genotype in each original herd. The results suggest that tracing back from index cattle to the original herd is an effective method to control bovine tuberculosis in beef cattle.

Mycobacterium bovis infection in a wild sow (Sus scrofa): first case in Korea

Mycobacterium (M.) bovis causes tuberculosis and has a broad host range, including humans, livestock, and wild animals. M. bovis infection of wild boar has been reported in several European countries. We report here the first case of M. bovis infection in a domesticated wild sow in Korea. Granulomatous and necrotizing lesions with small numbers of acid-fast bacilli were observed in nodules of the lung of wild sow. Furthermore, the M. bovis isolate from the wild sow had spoligotype SB0140 and a novel MIRU-VNTR allelic profile, which is not found in cattle and deer in Korea.

Extent of Mycobacterium bovis transmission among animals of dairy and beef cattle and deer farms in South Korea determined by variable-number tandem repeats typing

Identifying sources of Mycobacterium bovis transmission would be essential for establishing effective control programs of bovine tuberculosis (TB), a major zoonosis threatening human health worldwide. As an effort to determine the extent of M. bovis transmission among dairy and beef cattle and deer populations, a mycobacterial interspersed repetitive units (MIRU)-variable-number tandem repeats (VNTR) typing method was employed for analysis of 131 M. bovis isolates from 59 Holstein dairy cattle, 39 Korean beef cattle, and 33 deer. Of 31 MIRU-VNTR markers, 15 showed allelic diversity. The most discriminatory locus for M. bovis isolates was VNTR 3336 (h=0.59) followed by QUB 26, MIRU 31, VNTR 2401, and VNTR 3171 which showed high discriminatory power (h=0.43). The combined VNTR loci had an allelic diversity of 0.83. On the basis of the VNTR profiles of 30 VNTR loci, 24 genotypes were identified, and two genotypes were highly prevalent among all M. bovis isolates (33.6% and 19.1%, respectively), thus indicating that more than 50% of the isolates shared common molecular characteristics. Six additional genotypes were common in 2 of the 3 animal species, suggesting a wide interspecies transmission of M. bovis. This study thus demonstrates that MIRU-VNTR typing is useful in differentiation of M. bovis isolates and that M. bovis transmission occurs frequently among farmed animal species, highlighting the importance of bovine TB control programs in different animal species which are often raised in the same villages.

Performance of the SD Bioline TB Ag MPT64 Rapid test for quick confirmation of Mycobacterium bovis isolates from animals

Mycobacterium (M.) bovis, a bacterium in the M. tuberculosis complex, is a causative agent of bovine tuberculosis, a contagious disease of animals. Mycobacterial culture is the gold standard for diagnosing bovine tuberculosis, but this technique is laborious and time-consuming. In the present study, performance of the SD Bioline TB Ag MPT4 Rapid test, an immunochromatographic assay, was evaluated using reference bacterial strains and M. bovis field isolates collected from animals. The SD MPT64 Rapid test produced positive results for 95.5% (63/66) of the M. bovis isolates from cattle and 97.9% (46/47) of the isolates from deer. Additionally, the test had a sensitivity of 96.5% (95% CI, 91.2-99.0), specificity of 100% (95% CI, 96.7-100.0), positive predictive value of 100% (95% CI, 96.7-100.0), and negative predictive value of 92.9% (95% CI, 82.7-98.0) for M. bovis isolates. In conclusion, the SD MPT64 Rapid test is simple to use and may be useful for quickly confirming the presence of M. bovis in animals.

Genetic characterization and antimicrobial susceptibility of Campylobacter spp. isolated from domestic and imported chicken meats and humans in Korea

This study was conducted to examine the in vitro activity of antimicrobials against Campylobacter spp. isolates from chicken and human sources and the genetic interrelation among them. During 2004-2008, a total of 173 Campylobacter spp. isolated from chicken meats (60 domestic and 62 imported chicken meats) and humans (n = 51) were tested for susceptibility to nine antimicrobials. Of 173 isolates, 140 (80.9%) showed multidrug resistance (MDR) against three to eight antimicrobials. The most frequent pattern type was MDR to four antimicrobials: ciprofloxacin, nalidixic acid, ampicillin, and tetracycline. Over 52.6% (91/173) of the isolates tested were resistant to these four antibiotics simultaneously. Especially, two and five isolates originated from Korea and Brazil showed resistance against all antibiotics tested, except for florfenicol. Further, 95% (57/60) of the isolates originated from domestic chicken showed resistance to ciprofloxacin, the antimicrobial agent of choice for treatment of human campylobacteriosis. Genotypic characterization of all Campylobacter isolates performed by pulsed-field gel electrophoresis yielded 74 types among the 173 isolates. Isolates sharing the same or similar genetic clusters were detected in different countries at different times. The pulsed-field gel electrophoresis patterns of chicken-related isolates were closely related to those of isolates from humans with gastroenteritidis. The results of this study suggest that MDR Campylobacter spp. are widespread and that Campylobacter with similar genotypes are circulating both in humans and in chicken meat in Korea.

African swine fever virus

African swine fever virus (ASFV) is a large, intracytoplasmically-replicating DNA arbovirus and the sole member of the family Asfarviridae. It is the etiologic agent of a highly lethal hemorrhagic disease of domestic swine and therefore extensively studied to elucidate the structures, genes, and mechanisms affecting viral replication in the host, virus-host interactions, and viral virulence. Increasingly apparent is the complexity with which ASFV replicates and interacts with the host cell during infection. ASFV encodes novel genes involved in host immune response modulation, viral virulence for domestic swine, and in the ability of ASFV to replicate and spread in its tick vector. The unique nature of ASFV has contributed to a broader understanding of DNA virus/host interactions.