Comparative Pharmacokinetics of Gentamicin C1, C1a and C2 in Healthy and Infected Piglets

Gentamicin, an aminoglycoside antibiotic, is a mixture of therapeutically active C1, C1a, C2 and other minor components. Despite its decades-long use in pigs and other species, its intramuscular (IM) pharmacokinetics/pharmacodynamics (PKs/PDs) are unknown in piglets. Furthermore, the PKs of many drugs differ between healthy and sick animals. Therefore, we investigated the PKs of gentamicin after a single IM dose (10 mg/kg) in healthy piglets and piglets that were intranasally co-infected with Actinobacillus pleuropneumoniae and Pasteurella multocida (PM). The plasma concentrations were measured using validated liquid chromatography/mass spectrometry. The gentamicin exposure was 36% lower based on the area under the plasma concentration-time curve and 16% lower based on the maximum plasma concentration (Cmax) in the infected piglets compared to the healthy piglets, while it was eliminated faster (shorter half-life and larger clearance) in the infected piglets compared to the healthy piglets. The clearance and volume of distribution were the highest for the C1 component. C1, C1a and C2 accounted for 22-25%, 33-37% and 40-42% of the total gentamicin exposure, respectively. The PK/PD target for the efficacy of aminoglycosides (Cmax/minimum inhibitory concentration (MIC) > 10) could be exceeded for PM, with a greater magnitude in the healthy piglets. We suggest integrating this PK information with antibiotic susceptibility data for other bacteria to make informed antibiotic and dosage regimen selections against piglet infections.

Molecular Identification and Prevalence of the Mite Carpoglyphus lactis (Acarina: Carpoglyphidae) in Apis mellifera in the Republic of Korea

Apis mellifera, especially weak ones, are highly vulnerable to Carpoglyphus lactis mites, which can rapidly infest and consume stored pollen, leading to weakened colonies and potential colony collapse. This study aimed to ascertain and investigate the prevalence of this mite in honeybee colonies across nine provinces in the Republic of Korea (ROK). A total of 615 honeybee colony samples were collected from 66 apiaries during the spring and 58 apiaries during the summer of 2023. A 1242 bp segment of the Cytochrome c oxidase subunit 1 (COI) gene was amplified using the polymerase chain reaction method. The detection levels of C. lactis in the honeybees were compared between winter and summer. Based on the COI sequence analysis, the nucleotide sequence similarity of C. lactis mites isolated in the ROK with those from China (NC048990.1) was found to be 99.5%, and with those from the United Kingdom (KY922482.1) was 99.3%. This study is the first report of C. lactis in Korean apiaries. The findings of this study demonstrate a significantly higher detection rate in winter, which is 4.1 times greater than that in summer (p < 0.001). Furthermore, the results underscore the usefulness of molecular diagnostic techniques for detecting C. lactis mites.

Identification and pathogen detection of a Neocypholaelaps species (Acari: Mesostigmata: Ameroseiidae) from beehives in the Republic of Korea

In this study, we identified a new strain of the genus Neocypholaelaps from the beehives of Apis mellifera colonies in the Republic of Korea (ROK). The Neocypholaelap sp. KOR23 mites were collected from the hives of honeybee apiaries in Wonju, Gangwon-do, in May 2023. Morphological and molecular analyses based on 18S and 28S rRNA gene regions conclusively identified that these mites belong to the genus Neocypholaelaps, closely resembling Neocypholaelaps sp. APGD-2010 that was first isolated from the United States. The presence of 9 of 25 honeybee pathogens in these mite samples suggests that Neocypholaelaps sp. KOR23 mite may act as an intermediate vector and carrier of honeybee diseases. The identification of various honeybee pathogens within this mite highlights their significance in disease transmission among honeybee colonies. This comprehensive study provides valuable insights into the taxonomy and implications of these mites for bee health management and pathogen dissemination.

Re-emergence of foot-and-mouth disease in the Republic of Korea caused by the O/ME-SA/Ind-2001e lineage

The O/ME-SA/Ind-2001e foot-and-mouth disease virus (FMDV) lineage is a pandemic strain that has recently become dominant within East and Southeast Asia. During May 2023, this viral lineage spread to the Republic of Korea, where 11 outbreaks were detected on cattle and goat farms located in Cheongju and Jeungpyeong. Infected animals displayed typical FMD signs including vesicular lesions with drooling and anorexia. Molecular diagnostic testing and genetic analysis (VP1 sequencing) showed that the causative FMDVs belonged to the O/ME-SA/Ind-2001e lineage and shared the closest nucleotide identity (97.95-99.21%) to viruses that have been collected from Mongolia and South-East Asian countries. Phylogenetic analyses showed that these sequences were distinct to those collected from the previous Korean O/ME-SA/Ind-2001e lineage outbreaks in 2019, demonstrating that these cases are due to a new incursion of the virus into the country. Prompt implementation of emergency vaccination using antigenically matched serotype O vaccines (r1 value: 0.74-0.93), together with intensive active surveillance on farms surrounding the infected premises has successfully prevented further spread of FMD. These recent FMD outbreaks reinforce the importance of research to understand the risks associated with transboundary pathways in the region, in order to reduce the possibility of a further reintroduction of FMD into the Republic of Korea.

Surveillance and Genetic Analysis of Low-Pathogenicity Avian Influenza Viruses Isolated from Feces of Wild Birds in Mongolia, 2021 to 2023

The introduction of novel highly pathogenic (HPAI) viruses into Korea has been attributed to recombination events occurring at breeding sites in the Northern Hemisphere. This has increased interest in monitoring and genetically analyzing avian influenza viruses (AIVs) in northern regions, such as Mongolia, which share migratory bird flyways with Korea. AIVs in Mongolia were monitored by analyzing 10,149 fecal samples freshly collected from wild birds from April to October in 2021 to 2023. The prevalence of AIVs in wild birds was 1.01%, with a total of 77 AIVs isolated during these 3 years. These 77 AIVs included hemagglutinin (HA) subtypes H1, H2, H3, H4, H6, H10 and H13 and neuraminidase (NA) subtypes N1, N2, N3, N6, N7 and N8. The most frequently detected subtype combinations were H3N8 (39.0%) and H4N6 (19.5%), although HPAI viruses were not detected. Genetic analysis indicated that theses AIVs isolated from Mongolian samples were closely related to AIVs in wild birds in Korea, including those of Eurasian lineage. These findings indicate the necessity of continuous AIV surveillance and monitoring, as HPAI viruses introduced into Korea may derive from strains in Mongolia.

Calcium Chloride as a Novel Stabilizer for Foot-and-Mouth Disease Virus and Its Application in the Vaccine Formulation

The thermal stability of the in-house-developed foot-and-mouth disease (FMD) type O and A viruses was evaluated, and the O Jincheon virus was found to exhibit the lowest thermal stability. To overcome this instability, we proposed a novel stabilizer, calcium chloride. The thermal stability of FMDVs increased up to a CaCl2 concentration of 10 mM, and it had a decreasing trend at >30 mM. The O Jincheon virus showed a significant decrease in the amount of antigen over time at 4 °C. In contrast, the samples treated with CaCl2 showed stable preservation of the virus without significant antigen loss. After the CaCl2-formulated vaccine was administered twice to pigs, the virus neutralization titer reached approximately 1:1000, suggesting that the vaccine could protect pigs against the FMDV challenge. In summary, the O Jincheon virus is difficult to utilize as a vaccine given its low stability during storage after antigen production. However, following its treatment with CaCl2, it can be easily utilized as a vaccine. This study evaluated CaCl2 as a novel stabilizer in FMD vaccines and may contribute to the development of stable vaccine formulations, especially for inherently unstable FMDV strains.

An Amplicon-Based Application for the Whole-Genome Sequencing of GI-19 Lineage Infectious Bronchitis Virus Directly from Clinical Samples

Infectious bronchitis virus (IBV) causes a highly contagious respiratory disease in chickens, leading to significant economic losses in the poultry industry worldwide. IBV exhibits a high mutation rate, resulting in the continuous emergence of new variants and strains. A complete genome analysis of IBV is crucial for understanding its characteristics. However, it is challenging to obtain whole-genome sequences from IBV-infected clinical samples due to the low abundance of IBV relative to the host genome. Here, we present a novel approach employing next-generation sequencing (NGS) to directly sequence the complete genome of IBV. Through in silico analysis, six primer pairs were designed to match various genotypes, including the GI-19 lineage of IBV. The primer sets successfully amplified six overlapping fragments by long-range PCR and the size of the amplicons ranged from 3.7 to 6.4 kb, resulting in full coverage of the IBV genome. Furthermore, utilizing Illumina sequencing, we obtained the complete genome sequences of two strains belonging to the GI-19 lineage (QX genotype) from clinical samples, with 100% coverage rates, over 1000 × mean depth coverage, and a high percentage of mapped reads to the reference genomes (96.63% and 97.66%). The reported method significantly improves the whole-genome sequencing of IBVs from clinical samples; thus, it can improve understanding of the epidemiology and evolution of IBVs.

Prevalence and genome features of lake sinai virus isolated from Apis mellifera in the Republic of Korea

Lake Sinai Virus (LSV) is an emerging pathogen known to affect the honeybee (Apis mellifera). However, its prevalence and genomic characteristics in the Republic of Korea (ROK) remain unexplored. This study aimed to assess the prevalence of and analyze the LSVs by examining 266 honeybee samples from the ROK. Our findings revealed that LSV exhibited the highest infection rate among the pathogens observed in Korean apiaries, particularly during the reported period of severe winter loss (SWL) in A. mellifera apiaries in 2022. Three LSV genotypes- 2, 3, and 4 -were identified using RNA-dependent RNA polymerase gene analysis. Importantly, the infection rates of LSV2 (65.2%) and LSV3 (73.3%) were significantly higher in colonies experiencing SWL than in those experiencing normal winter loss (NWL) (p < 0.03). Furthermore, this study provides the first near-complete genome sequences of the Korean LSV2, LSV3, and LSV4 strains, comprising 5,759, 6,040, and 5,985 nt, respectively. Phylogenetic analysis based on these near-complete genome sequences demonstrated a close relationship between LSVs in the ROK and China. The high LSV infection rate in colonies experiencing a heightened mortality rate during winter suggests that this pathogen might contribute to SWL in ROK. Moreover, the genomic characteristic information on LSVs in this study holds immense potential for epidemiological information and the selection of specific genes suitable for preventing and treating LSV, including the promising utilization of RNA interference medicine in the future.

Evaluation of Foot-and-Mouth Disease (FMD) Virus Asia1 Genotype-V as an FMD Vaccine Candidate: Study on Vaccine Antigen Production Yield and Inactivation Kinetics

South Korea has experienced outbreaks of foot-and-mouth disease (FMD) of serotypes O and A, leading to nationwide vaccination with a bivalent vaccine. Since the FMD virus (FMDV) Asia1 group-V genotype occurred in North Korea in 2007, an Asia1/MOG/05 vaccine strain belonging to the Asia1 group-V genotype was developed using a genetic recombination method (Asia1/MOG/05-R). This study aimed to evaluate the antigen productivity and viral inactivation kinetics of Asia1/MOG/05-R to assess its commercial viability. The antigen yield of Asia1/MOG/05-R produced in flasks and bioreactors was approximately 4.0 μg/mL. Binary ethylenimine (BEI) inactivation kinetics of Asia1/MOG/05-R showed that 2 mM and 1.0 mM BEI treatment at 26 °C and 37 °C, respectively, resulted in a virus titer <10-7 TCID50/mL within 24 h, meeting the inactivation kinetics criteria. During incubation at 26 °C and 37 °C, 10% antigen loss occurred, but not due to BEI treatment. When pigs were inoculated twice with the Asia1/MOG/05-R antigen, the virus neutralization titer increased to approximately 1:1000; therefore, it can sufficiently protect against Asia1/MOG/05-R and Asia1 Shamir viruses. The Asia1/MOG/05-R will be useful as a vaccine strain for domestic antigen banks.

Characterization and Spike Gene Analysis of a Candidate Attenuated Live Bovine Coronavirus Vaccine

The bovine coronavirus (BCoV) KBR-1 strain, obtained from calf diarrhea samples collected in 2017, belongs to group GIIa. To attenuate this strain, it was subcultured continuously (up to 79 times) in HRT-18 cells, followed by 80-120 passages in MDBK cells. The KBR-1-p120 strain harvested from MDBK cells at passage 120 harbored 13 amino acid mutations in the spike gene. Additionally, the KBR-1-p120 strain showed a high viral titer and cytopathogenic effects in MDBK cells. Seven-day-old calves (negative for BCoV antigen and antibodies) that did not consume colostrum were orally inoculated with the attenuated candidate strain (KBR-1-p120), or with KBR-1 passaged 10 times (KBR-1-p10) in HRT-18 cells. Calves inoculated with KBR-1-p10 had a low diarrhea score, and BCoV RNA was detected at 3-7 days post-inoculation (DPI). The virus was also present in the duodenum, jejunum, and ileum at autopsy; however, calves inoculated with KBR-1-p120 had low levels of BCoV RNA in feces at 4-6 DPI, and no diarrhea. In addition, an extremely small amount of BCoV RNA was present in the jejunum and ileum at autopsy. The small intestines of calves inoculated with KBR-1-p120 were emulsified and used to infect calves two more times, but pathogenicity was not recovered. Therefore, the KBR-1-p120 strain has potential as a live vaccine candidate.

The First Report on the Complete Sequence Characterization of Bluetongue Virus Serotype 3 in the Republic of Korea

The bluetongue virus (BTV) is a significant animal pathogen with economic implications in the ruminant industry. Despite global reports on BTV detection and epidemiologic investigations, limited studies have focused on the virus in the ROK. In this study, BTV epidemiological research was conducted on blood samples from cattle and goat farms across nine regions during 2013-2014. The results showed that 3.33% of bovine blood samples (194/5824) and 0.19% of goat blood samples (2/1075) tested positive for BTV antibodies using ELISA. In Jeju-do, BTV RNA amplification occurred in 51 of 422 samples (12.1%) using real-time reverse transcription (RT-qPCR). The isolation of one sample revealed it as serotype 3, as indicated by the sequence of segments 2 (Seg-2) and 6 (Seg-6), associated with the eastern BTV topotype. However, based on Seg-1, -3, -4, -5, -7, -8, -9, and -10 analyses, the BTV-3/JJBB35 strain is more closely related to distinct BTV strains. These findings imply BTV circulation and that the Korean-isolated BTV might originate from Asian BTV strains due to multiple reassortment events. This study provides foundational data for ongoing BTV monitoring and disease-control policies in the ROK.

Evaluation of a Vaccine Candidate Designed for Broad-Spectrum Protection against Type A Foot-and-Mouth Disease in Asia

Foot-and-mouth disease (FMD) vaccines are currently the most powerful protective and preventive measures used to control FMD. In this study, the chimeric vaccine strain containing antigenic epitopes from the FMD virus serotype A, which belongs to the ASIA topotype, was produced and evaluated. The chimeric vaccine strains contain sea-97/G1 (VP4, VP2, VP3) and A22 Iraq (VP1) or G-VII (VP1) for use in FMD vaccines in Asia. The 50% protective dose was determined in mice. Vaccinated mice were challenged with three different type A viruses (Sea-97/G1, Sea-97/G2, G-VII clade) seven days post-vaccination (dpv), and mice that received the vaccine candidates were protected against the three viruses. The protective capability of one of the vaccine candidates was evaluated in pigs. Vaccinated pigs were challenged with three different type A viruses (Sea-97/G1, Sea-97/G2, G-VII clade) at 28 dpv, and pigs that received the vaccine candidate were protected against the three viruses. The results showed that this vaccine candidate, which was designed to provide protection against FMD in Asia, efficiently protected pigs against virus challenge and thus has potential as a broad-spectrum vaccine for various epidemic FMD viruses.

Ethyl Formate Fumigation against Pineapple Mealybug, Dysmicoccus brevipes, a Quarantine Insect Pest of Pineapples

Pineapple mealybug, Dysmicoccus brevipes (Hemiptera: Pseudococcidae), is a significant pest in pineapple production and a key trade barrier. We explored the potential use of ethyl formate (EF) as a methyl bromide alternative for the postharvest fumigation of D. brevipes in imported pineapples. When treated at 8 °C for 4 h, EF fumigation was effective against D. brevipes with LCt99, the lethal concentration × time product of EF necessary to achieve 99% mortality of D. brevipes nymphs and adults at 64.2 and 134.8 g h/m3, respectively. Sorption trials conducted with 70 g/m3 EF for 4 h at 8 °C using 7.5, 15 and 30% pineapple loading ratios (w/v) indicated that loading ratio lower than 30% is necessary to achieve the LCt99 values required to control D. brevipes. In a scaled up trial using 1 m3 chamber, EF fumigation with 70 g/m3 for 4 h at 8 °C with 20% pineapple loading ratio (w/v) resulted in a complete control of D. brevipes treated. There were no significant differences in hue values, sugar contents, firmness, and weight loss between EF-treated and untreated pineapples. Our results suggest that EF is a promising alternative to methyl bromide fumigation for the postharvest phytosanitary disinfection of D. brevipes in pineapples.

Insights on reproduction-related genes in the striped fruit fly, Zeugodacus scutellata (Hendel) (Diptera: Tephritidae)

The striped fruit fly, Zeugodacus scutellata is a significant pest in East and Southeast Asia by damaging Cucurbitaceae blossoms and fruits. To control this pest, a novel strategy to suppress the gene(s) associated with sexually dimorphic phenotypes has been devised and implemented in a laboratory scale. However, comprehensive transcriptomic analysis related to this sex differentiation of Z. scutellata was necessary to determine effective target genes for the genetic control. We performed de novo assembly of the transcript obtained by paired-end sequencing using an Illumina HiSeq platform and let to 217,967 unigenes (i.e., unique genes) with a minimum length of 200 bp. The female produced 31, 604, 442 reads with 97.93% of Q20, 94.76% of Q30, and the male produced 130, 592, 828 reads with 97.93% of Q20 and 94.76 of Q30%. The differentially expressed genes were used to predict genetic factors associated with sex differentiation, which included Rho1, extra-macrochaetae (emc), hopscotch (hop), doublesex (dsx), sex-lethal (sxl), transformer-2 (tra-2), testis-specific serine/threonine-protein kinase (tssk1), tektin1 (tkt1) and 2 (tkt2), odorant binding proteins (OBPs), fruitless (fru), vitellogenin receptor, and hormone receptors in Z. scutellata. In addition, this transcriptome analysis provides the additional gene associated with sex determination and mating behaviors, which would be applied to develop a novel sterile insect technique against Z. scutellata.

Antimicrobial Resistance in Escherichia coli Isolated from Healthy Dogs and Cats in South Korea, 2020-2022

The occurrence of antimicrobial-resistant bacteria in companion animals poses public health hazards globally. This study aimed to evaluate the antimicrobial resistance profiles and patterns of commensal E. coli strains obtained from fecal samples of healthy dogs and cats in South Korea between 2020 and 2022. In total, 843 E. coli isolates (dogs, n = 637, and cats, n = 206) were assessed for susceptibility to 20 antimicrobials. The resistance rates of the most tested antimicrobials were significantly higher in dog than in cat isolates. Cefalexin (68.9%) demonstrated the highest resistance rates, followed by ampicillin (38.3%), tetracycline (23.1%), and cefazolin (18.7%). However, no or very low resistance (0-0.6%) to amikacin, imipenem, piperacillin, and colistin was found in both dog and cat isolates. Overall, 42.3% of the isolates exhibited multidrug resistance (MDR). MDR in isolates from dogs (34.9%) was significantly higher than in those from cats (20.9%). The main components of the resistance patterns were cefalexin and ampicillin in both dog and cat isolates. Additionally, MDR patterns in isolates from dogs (29.2%) and cats (16%) were shown to encompass five or more antimicrobials. Multidrug-resistant commensal E. coli could potentially be spread to humans or other animals through clonal or zoonotic transmission. Therefore, the incidence of antimicrobial resistance in companion animals highlights the urgent need to restrict antimicrobial resistance and ensure the prudent use of antimicrobials in Korea.

Complete Genomic Characterization of Lumpy Skin Disease Virus Isolates from Beef Cattle in Lopburi Province, Central Thailand, during 2021-2022

Lumpy skin disease (LSD) is a viral infection that impacts the cattle industry. The most efficient approach to prevent disease involves the utilization of live-attenuated LSD vaccines (LAVs), which stands out as the most successful method. However, LAVs might be subjected to changes to their genomes during replication that increase viral infectivity or virulence. The objective of this study was to monitor alterations in the genetic characteristics of the lumpy skin disease virus (LSDV) in beef cattle following the administration of LAVs in Lopburi Province of Central Thailand. A total of four skin samples from LSD cases were collected from non-vaccinated animals that exhibited LSD clinical symptoms from two distinct districts, spanning three subdistricts within the region. The samples of cattle were analyzed using real-time PCR targeting the LSDV074 p32 gene, the virus was isolated, and the entire genome sequences were evaluated through a single nucleotide polymorphisms (SNPs) analysis, and phylogenetic trees were assembled. The investigations revealed that LSDVs from two isolates from Chai Badan district exhibited significant mutations in the open reading frame (ORF) 023 putative protein, while another two isolates from Lam Sonthi district had a change in the untranslated region (UTR). For a result, the most proficient disease diagnosis and control should be evaluated on viral genetics on a regular basis.

An Alternative Serological Measure for Assessing Foot-and-Mouth Disease Vaccine Efficacy against Homologous and Heterologous Viral Challenges in Pigs

To analyze the relationship between homologous and heterologous serological titers of immunized pigs and their protection statuses against FMD virus challenges, in the present study, the correlation between the virus neutralization titers at 21 and 28 dpv and the protection statuses at 28 dpv against challenge with FMD virus was analyzed using data sets comprising five different combinations of homologous or heterologous challenge experiments in pigs vaccinated with type O (n = 96), A (n = 69), and Asia 1 (n = 74). As a result, the experiments were divided into three groups (21D-1, 21D-2, and 21D-3) in the 21-dpv model and two groups (28D-1 and 28D-2) in the 28-dpv model. Each response curve of groups 21D-1 and 21D-2 in the 21-dpv model was very similar to each curve of groups 28D-1 and 28D-2 in the 28-dpv model, respectively, even though there was an exceptional extra group (21D-3) in the 21-dpv model. The average titers estimating 0.75 probability of protection ranged from 1.06 to 1.62 log10 in the 21-dpv model and from 1.26 to 1.64 log10 in the 28-dpv model. In summary, we demonstrated that the serological method is useful for predicting the homologous and heterologous protection statuses of vaccinated pigs.

Comparative Pharmacokinetics and Bioequivalence of Pour-On Ivermectin Formulations in Korean Hanwoo Cattle

This study aimed to conduct a bioequivalence study of applying three pour-on ivermectin formulations at a dose of 1 mg/kg on the back of Korean native beef cattle (Hanwoo). To conduct bioequivalence testing, the pharmacokinetics of three groups (control Innovator, test Generic A, and test Generic B) of five clinically healthy Korean Hanwoo cattle (average weight 500 kg) were studied. After topical application to the skin, blood samples were drawn at the indicated times. These blood samples were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The time required to reach the maximum concentration (Tmax), the maximum concentration (Cmax), and the area under the curve (AUClast) of each pharmacokinetic parameter were compared for bioequivalence. The results showed that the control had a Tmax of 41 ± 1.24 h, a Cmax of 0.11 ± 0.01 μg/mL, and an AUClast of 9.33 ± 0 h*μg/mL). The comparator Generic A had a Tmax of 40 ± 1.14 h, a Cmax of 0.10 ± 0.01 (μg/mL, and an AUClast of 9.41 ± 0.57 h*μg/mL, while Generic B had a Tmax of 40 ± 2.21 h, a Cmax of 0.10 ± 0.01 μg/mL, and an AUClast of 9 h*μg/mL. The values of the bioequivalence indicators Cmax, Tmax, and AUC were all within the range of 80% to 120%, confirming that all three tested formulations were bioequivalent. In conclusion, the study showed that the two generic products were bioequivalent to the original product in Hanwoo cattle.

Antimicrobial Resistance Profiles of Enterococcus faecium and Enterococcus faecalis Isolated from Healthy Dogs and Cats in South Korea

Enterococcus spp. are typically found in the gastrointestinal tracts of humans and animals. However, they have the potential to produce opportunistic infections that can be transmitted to humans or other animals, along with acquired antibiotic resistance. In this study, we aimed to investigate the antimicrobial resistance profiles of Enterococcus faecium and Enterococcus faecalis isolates obtained from companion animal dogs and cats in Korea during 2020-2022. The resistance rates in E. faecalis towards most of the tested antimicrobials were relatively higher than those in E. faecium isolated from dogs and cats. We found relatively higher resistance rates to tetracycline (65.2% vs. 75.2%) and erythromycin (39.5% vs. 49.6%) in E. faecalis isolated from cats compared to those from dogs. However, in E. faecium, the resistance rates towards tetracycline (35.6% vs. 31.5%) and erythromycin (40.3% vs. 35.2%) were comparatively higher for dog isolates than cats. No or very few E. faecium and E. faecalis isolates were found to be resistant to daptomycin, florfenicol, tigecycline, and quinupristin/dalfopristin. Multidrug resistance (MDR) was higher in E. faecalis recovered from cats (44%) and dogs (33.9%) than in E. faecium isolated from cats (24.1%) and dogs (20.5%). Moreover, MDR patterns in E. faecalis isolates from dogs (27.2%) and cats (35.2%) were shown to encompass five or more antimicrobials. However, E. faecium isolates from dogs (at 13.4%) and cats (at 14.8%) were resistant to five or more antimicrobials. Taken together, the prevalence of antimicrobial-resistant enterococci in companion animals presents a potential public health concern.

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.

Tracking the contamination sources of microbial population and characterizing Listeria monocytogenes in a chicken slaughterhouse by using culture-dependent and -independent methods

Listeria monocytogenes is the etiologic agent of listeriosis, a foodborne disease that poses a threat to public health globally. Chicken meat exhibits heightened susceptibility to L. monocytogenes contamination during butchery. The persistence of this pathogen in the slaughterhouse environment enables recurring contamination of meat products. This study aimed at identifying the sources and transmission routes of L. monocytogenes contamination within an abattoir where it was consistently detected for three consecutive years (2019-2021). Furthermore, the environmental factors aiding contamination along chicken processing lines were determined by surveying the microbiome within the facility. Samples collected in 2019 to 2021 were subjected to culture-dependent analysis to assess the prevalence, serotypes, and multi-locus sequence typing (MLST) of L. monocytogenes. Additionally, the specimens collected in 2021 underwent culture-independent analysis via real-time quantitative polymerase chain reaction (qPCR) and 16S rRNA gene amplicon sequencing to identify the contamination sources and characterize the entire microbial community within the slaughterhouse. L. monocytogenes was isolated only from the clean zone, where the final slaughtering stage occurs. Most strains isolated from the final carcasses showed the same genetic cluster as the isolate in the chilling water and were assigned to MLST profile ST3. Culture-independent qPCR confirmed L. monocytogenes contamination in all samples, excluding post-scalding carcasses, prewashed post-evisceration carcasses, and the bleeding areas. Consequently, qPCR enabled more comprehensive identification of L. monocytogenes contamination points than culture-dependent approaches. Moreover, 16S rRNA gene amplicon sequencing demonstrated that psychro-tolerant and spoilage-related bacteria with L. monocytogenes-like attributes exhibited enhanced viability in the clean zone and immersion-chilling water. Metagenomics-based source tracking analysis further revealed that the shackles and chilling waters represent predominant sources of cross-contamination between different slaughterhouse zones, whereas the grading and packaging workstations and chilling water in the clean zone were deemed crucial sources affecting final carcass contamination. Collectively, these findings demonstrate through culture-dependent and -independent methods that L. monocytogenes spreads along the slaughter line, contaminating the slaughterhouse. Moreover, by investigating changes in microbial community and bacterial flow along the slaughter line within the facility, the sources influencing carcass contamination can be effectively traced.

Evaluation of Biological Equivalence for Generic Tulathromycin Injections in Cattle

The recent expiration of patents for the antibiotic tulathromycin has led to a significant increase in the number of generic tulathromycin products (GTPs) available. This study aims to evaluate the bioequivalence of four GTPs, which experienced a rapid increase in market share. The bioequivalence was evaluated by performing pharmacokinetic assessments. The four selected GTPs (Tulaject, Tulagen, Toulashot, and T-raxxin) were compared with the reference product, Draxxin. A dose of 2.5 mg/kg.bw/day was administered via subcutaneous injection, and blood samples were collected 460 times from 20 Holstein cattle. Plasma concentrations of tulathromycin were measured over time using LC-MS/MS analysis. Bioequivalence was evaluated using a statistical program for pharmacokinetic parameters, including the area under the concentration time curve (AUC) and the maximum plasma concentration (Cmax). The bioequivalence was considered proven if the difference between the test and reference products was within 20% for both AUC and Cmax. The results showed that the confidence interval (CI, 90%) for both AUC and Cmax values was within the 80~120% range, demonstrating the bioequivalence of the four GTPs compared to Draxxin. This study provides evidence for the bioequivalence of the selected GTPs, contributing to their validation for use as effective antibiotics.

Intrahepatic Cholangiocarcinoma Identified in a Zoo-Housed Sandhill Crane (Grus canadensis): An Anatomopathological and Metagenomic Study

Tumors in birds can be caused by a variety of factors such as species, age, sex, virus, chemicals, and environment. In particular, tumors are a major cause of death in long-lived birds such as parrots and zoo birds. A male sandhill crane that was bred for 8 years in a zoo was diagnosed with intrahepatic cholangiocarcinoma (ICC). At necropsy, the liver revealed a multinodular mass of variable colors, and severe cirrhosis and hemorrhages were present. Histologically, ICC was characterized by the presence of both types of ICC: small-duct type and large-duct type. Large-duct-type ICC was distinguished by the presence of multifocal biliary neoplasia, characterized by the diffuse papillary proliferation of columnar cells resembling large cholangiocytes. Small-duct-type ICC was characterized by the presence of non-mucin-producing cuboidal cells such as bile duct cells. In this case, no viral cause was identified from the metagenomic analysis and PCR of ICC; however, a contributing role of Cutibacterium sp. and E. coli identified from the metagenomics could not be excluded. This study is the first to describe the anatomopathological characteristics of ICC in the studied sandhill crane and attempts to determine its potential infectious etiology using metagenomics.

Bestatin, A Pluripotent Immunomodulatory Small Molecule, Drives Robust and Long-Lasting Immune Responses as an Adjuvant in Viral Vaccines

An inactivated whole-virus vaccine is currently used to prevent foot-and-mouth disease (FMD). Although this vaccine is effective, it offers short-term immunity that requires regular booster immunizations and has several side effects, including local reactions at the vaccination site. To address these limitations, herein, we evaluated the efficacy of bestatin as a novel small molecule adjuvant for inactivated FMD vaccines. Our findings showed that the FMD vaccine formulated with bestatin enhanced early, intermediate-, and particularly long-term immunity in experimental animals (mice) and target animals (pigs). Furthermore, cytokines (interferon (IFN)α, IFNβ, IFNγ, and interleukin (IL)-29), retinoic acid-inducible gene (RIG)-I, and T-cell and B-cell core receptors (cluster of differentiation (CD)28, CD19, CD21, and CD81) markedly increased in the group that received the FMD vaccine adjuvanted with bestatin in pigs compared with the control. These results indicate the significant potential of bestatin to improve the efficacy of inactivated FMD vaccines in terms of immunomodulatory function for the simultaneous induction of potent cellular and humoral immune response and a long-lasting memory response.

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.

Spike Gene Analysis and Prevalence of Porcine Epidemic Diarrhea Virus from Pigs in South Korea: 2013-2022

From late 2013-2022, 1131 cases of porcine epidemic diarrhea (PED) were reported to the Korean Animal Health Integrated System (KAHIS). There were four major outbreaks from winter to spring (2013-2014, 2017-2018, 2018-2019, and 2021-2022), with the main outbreaks occurring in Chungnam (CN), Jeonbuk (JB), and Jeju (JJ). Analysis of the complete spike (S) gene of 140/1131 KAHIS PEDV cases nationwide confirmed that 139 belonged to the G2b genotype and 1 to the G2a genotype. Among them, two strains (K17GG1 and K17GB3) were similar to an S INDEL isolated in the United States (strain OH851), and 12 strains had deletions (nucleotides (nt) 3-99) or insertions (12 nt) within the S gene. PEDVs in JJ formed a regionally independent cluster. The substitution rates (substitutions/site/year) were as follows: 1.5952 × 10-3 in CN, 1.8065 × 10-3 in JB, and 1.5113 × 10-3 in JJ. A Bayesian skyline plot showed that the effective population size of PEDs in JJ fell from 2013-2022, whereas in CN and JB it was maintained. Genotyping of 340 Korean PEDV strains, including the 140 PEDVs in this study and 200 Korean reference strains from GenBank, revealed that only the highly pathogenic non-INDEL type (G2b) was dominant from 2020 onwards. Therefore, it is predicted that the incidence of PED will be maintained by the G2b (non-INDEL) genotype.

Safety and Immunogenicity of Chimeric Pestivirus KD26_E2LOM in Piglets and Calves

A chimeric pestivirus (KD26_E2LOM) was prepared by inserting the E2 gene of the classical swine fever virus (CSFV) LOM strain into the backbone of the bovine viral diarrhea virus (BVDV) KD26 strain. KD26_E2LOM was obtained by transfecting the cDNA pACKD26_E2LOM into PK-15 cells. KD26_E2LOM chimeric pestivirus proliferated to titers of 106.5 TCID50/mL and 108.0 TCID50/mL at 96 h post-inoculation into PK-15 cells or MDBK cells, respectively. It also reacted with antibodies specific for CSFV E2 and BVDV Erns, but not with an anti-BVDV E2 antibody. Piglets (55-60 days old) inoculated with a high dose (107.0 TCID50/mL) of KD26_E2LOM produced high levels of CSFV E2 antibodies. In addition, no co-habiting pigs were infected with KD26_E2LOM; however, some inoculated pigs excreted the virus, and the virus was detected in some organs. When pregnant sows were inoculated during the first trimester (55-60 days) with a high dose (107.0 TCID50/mL) of KD26_E2LOM, anti-CSFV E2 antibodies were produced at high levels; chimeric pestivirus was detected in one fetus and in the ileum of one sow. When 5-day-old calves that did not consume colostrum received a high dose (107.0 TCID50/mL) of KD26_E2LOM, one calf secreted the virus in both feces and nasal fluid on Day 2. A high dose of KD26_E2LOM does not induce specific clinical signs in most animals, does not spread from animal to animal, and generates CSFV E2 antibodies with DVIA functions. Therefore, chimeric pestivirus KD26_E2LOM is a potential CSFV live marker vaccine.

Development of a Novel Korean H9-Specific rRT-PCR Assay and Its Application for Avian Influenza Virus Surveillance in Korea

Since the 2000s, the Y439 lineage of H9N2 avian influenza virus (AIV) has been the predominant strain circulating in poultry in Korea; however, in 2020, the Y280 lineage emerged and spread rapidly nationwide, causing large economic losses. To prevent further spread and circulation of such viruses, rapid detection and diagnosis through active surveillance programs are crucial. Here, we developed a novel H9 rRT-PCR assay that can detect a broad range of H9Nx viruses in situations in which multiple lineages of H9 AIVs are co-circulating. We then evaluated its efficacy using a large number of clinical samples. The assay, named the Uni Kor-H9 assay, showed high sensitivity for Y280 lineage viruses, as well as for the Y439 lineage originating in Korean poultry and wild birds. In addition, the assay showed no cross-reactivity with other subtypes of AIV or other avian pathogens. Furthermore, the Uni Kor-H9 assay was more sensitive, and had higher detection rates, than reference H9 rRT-PCR methods when tested against a panel of domestically isolated H9 AIVs. In conclusion, the novel Uni Kor-H9 assay enables more rapid and efficient diagnosis than the "traditional" method of virus isolation followed by subtyping RT-PCR. Application of the new H9 rRT-PCR assay to AI active surveillance programs will help to control and manage Korean H9 AIVs more efficiently.

Epidemiological and Molecular Approaches for a Fatal Feline Panleukopenia Virus Infection of Captive Siberian Tigers (Panthera tigris altaica) in the Republic of Korea

Feline panleukopenia virus (FPV), a member of the species Protoparvovirus carnivoran1, is one of the most fatal pathogens of domestic and wild carnivores. The virus endemically infects domestic carnivores worldwide and its cross-species transmission threatens endangered wild carnivores, including Siberian tigers. In this study, a fatal FPV infection in endangered Siberian tigers was investigated to trace the origin of the virus and elucidate the reason behind FPV's infection of the vaccinated tigers. Our genetic characterization and phylogenetic analysis revealed that the virus detected in the infected tigers, designated as the KTPV-2305 strain, was closely related to FPV strains circulating in Korean cats, suggesting that it might have been transmitted from stray cats wandering around the zoo. Compared with the prototype FPV reference strains, the KTPV-2305 strain carried three distinct amino acid (aa) mutations in the VP2 protein sequence (I101T, I232V, and L562V) in this study. These three mutations are commonly found in most global FPV strains, including Korean strains, indicating that these mutations are common evolutionary characteristics of currently circulating global FPVs. The reason why the vaccinated tigers were infected with FPV was most likely the insufficient protective immunity of the affected tigress or vaccine failure triggered by the interference of maternal-derived antibodies in the affected tiger cubs. These findings suggest that improved vaccination guidelines are urgently needed to save the lives of wild carnivores from this fatal virus.

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.

Serological Conversion through a Second Exposure to Inactivated Foot-and-Mouth Disease Virus Expressing the JC Epitope on the Viral Surface

Foot-and-mouth disease (FMD) is a fatal contagious viral disease that affects cloven-hoofed animals and causes severe economic damage at the national level. There are seven serotypes of the causative foot-and-mouth disease virus (FMDV), and type O is responsible for serious outbreaks and shows a high incidence. Recently, the Cathay, Southeast Asia (SEA), and ME-SA (Middle East-South Asia) topotypes of type O have been found to frequently occur in Asia. Thus, it is necessary to develop candidate vaccines that afford protection against these three different topotypes. In this study, an experimental FMD vaccine was produced using a recombinant virus (TWN-JC) with the JC epitope (VP1 140-160 sequence of the O/SKR/Jincheon/2014) between amino acid 152 and 153 of VP1 in TWN-R. Immunization with this novel vaccine candidate was found to effectively protect mice against challenge with the three different topotype viruses. Neutralizing antibody titers were considerably higher after a second vaccination. The serological differences between the topotype strains were identified in guinea pigs and swine. In conclusion, a significant serological difference was observed at 56 days post-vaccination between animals that received the TWN-JC vaccine candidate and those that received the positive control virus (TWN-R). The TWN-JC vaccine candidate induced IFNγ and IL-12B.

Pathogenicity and Pathological Characteristics of African Swine Fever Virus Strains from Pig Farms in South Korea from 2022 to January 2023

Since the first African swine fever (ASF) outbreak occurred at a pig farm in South Korea in September 2019, as of 31 January 2023, 31 ASF cases have occurred at pig farms, while 2799 ASF virus (ASFV)-infected wild boars have been identified. The circulation of ASFV in wild boar populations poses a high risk of spillover to pig farms in the country. However, information on the changes in the pathogenicity of Korean ASFV strains from wild boars is not available. Investigating the pathogenicity of ASFV strains from pig farms is the only way to predict their alterations. In a previous study, no changes in the pathogenicity of ASFV strains circulating during 2019-2021 were identified through animal experiments. In this study, we chose two ASFV strains with potentially reduced pathogenicity among ten viruses obtained from pig premises from 2022 to January 2023 and estimated their pathogenicities and pathological characteristics. All the inoculated pigs died 8-10 days post-inoculation after showing pyrexia, depression, anorexia, and recumbency together with the common pathological lesions of enlarged hemorrhagic lymph nodes and splenomegaly with infarction. These results support that the pathogenicity among ASFV isolates in South Korea still remained unchanged during the study period.

The Development of Novel Reverse Transcription Loop-Mediated Isothermal Amplification Assays for the Detection and Differentiation of Virulent Newcastle Disease Virus

Newcastle disease (ND) is a highly pathogenic viral infection of poultry with significant economic impacts worldwide. Despite the widespread use of vaccines, ND outbreaks continue to occur even within vaccinated poultry farms. Furthermore, novel Newcastle disease virus (NDV) genotypes are emerging in poultry, increasing the need for the development of rapid, accurate, and simple diagnostic methods. We therefore developed two novel sets of visual reverse transcription loop-mediated isothermal amplification (RT-LAMP) assays based on highly conserved regions of the HN and F genes. The limits of detection of the NDV-Common-LAMP assay, for all the NDV strains, were 103.0 EID50/0.1 mL for Kr005 and 102.0 EID50/0.1 mL for Lasota within 35 min. The sensitivity of the NDV-Patho-LAMP assay, used for the strain differentiation of virulent NDV, was 102.0 EID50/0.1 mL for Kr005. No amplification was detected for the non-NDV templates. Next, we probed 95 clinical strains and 7 reference strains with the RT-LAMP assays to assess the feasibility of their use in diagnostics. We observed no cross-reactivity across the 102 strains. Furthermore, there was 100% congruence between the RT-LAMP assays and full-length sequencing of the target genes, indicating the potential for visual RT-LAMP in the identification and differentiation of NDV. These novel RT-LAMP assays are ideally suited for the field or resource-limited environments to facilitate the faster detection and differentiation of NDV, which can reduce or avoid further spread.

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.

Development of a Concurrent Treatment Technique of Ethyl Formate and Mixtures (Nitrogen, Phosphine) to Control Citrus Mealybug (Planococcus citri)

Currently, the fumigant ethyl formate (EF) is stored as a liquified gas in metal cylinders mixed with carbon dioxide (CO2), but this product type is expensive to manufacture, transport, and maintain in cylinders. To address these problems, we developed a new EF fumigation technique with a nitrogen (N2) carrier. In this report, the susceptibility of citrus mealybugs, one of the most resistant mealybugs to fumigants, to EF was assessed; the phytotoxicity of an EF + N2 concurrent treatment applied to banana fruit was examined to evaluate the efficacy compared to the current EF + CO2 product; and the increased efficacy with a phosphine (PH3) addition to EF + N2 was also assessed. Concurrent treatment of EF and N2 was performed at an LC50 concentration of EF. N2 was applied in seven doses from concentrations of 79% to 95%. The phytotoxicity of EF to bananas was assessed by applying EF at 35 mg/L with N2 at 79%, and the color, sugar content, and weight loss of bananas were measured for 14 days after treatment. The EF with N2 treatment resulted in more than 50% mortality at all growth stages of the mealybug, and there was no significant difference between the untreated and treated banana fruits. EF mixed with PH3 showed a higher efficacy than treatment with EF alone, but only a slight increase in efficacy was observed when the PH3 concentration increased. These results indicate that concurrent treatment with EF and N2 can be used to control mealybugs on banana fruits, and combined treatment with EF and PH3 can also enhance the efficacy against mealybugs.

Pectobacterium jejuense sp. nov. Isolated from Cucumber Stem Tissue

A single Pectobacterium-like strain named 13-115T was isolated from a specimen of diseased cucumber stem tissue collected on Jeju Island, South Korea. The strain presented a rod-like shape and was negative for Gram staining. When grown on R2A medium at 25 °C, strain 13-115T formed round, convex and white colonies. This strain showed growth at temperatures ranging from 10 to 30 °C and tolerated a pH range of 6-9. The strain could also tolerate NaCl concentrations up to 5%. Analysis of the 16S rRNA gene sequence revealed that strain 13-115T exhibited similarity of over 99% with Pectobacterium brasiliense, P. carotovorum, P. polaris, and P. parvum. By conducting multilocus sequence analyses using dnaX, leuS, and recA genes, a separate phylogenetic lineage was discovered between strain 13-115T and other members of the genus Pectobacterium. Moreover, the strain showed relatively low in silico DNA-DNA hybridization (<60.6%) and average nucleotide identity (ANI) (<94.9%) values with recognized Pectobacterium species. The isolate has a genome size of 5,069,478 bp and a genomic G + C content of 52.04 mol%. Major fatty acids identified in the strain included C16:0 (28.99%), summed feature 3 (C16:1 ω7c and/or C16:1 ω6c; 28.85%), and C18:1 ω7c (19.01%). Pathogenicity assay confirmed that the novel strain induced soft rot symptoms in cucumber plants and Koch's postulates were fulfilled. Molecular analysis and phenotypic data indicated that strain 13-115T could be classified as a new species within the Pectobacterium genus, which has been named Pectobacterium jejuense. The type strain is 13-115T (= KCTC 92800T = JCM 35940T).

Rescue of a Live-Attenuated Porcine Epidemic Diarrhea Virus HSGP Strain Using a Virulent Strain and a Partially Attenuated Strain

In South Korea in 2013, the G1-based vaccine failed to prevent an outbreak of G2b-type porcine epidemic diarrhea virus (PEDV), which is more pathogenic than the traditional G1-type strain, thereby allowing the virus to spread. In 2017 and 2018, field samples were cultured sequentially on Vero cells to isolate HS (virulent) and SGP-M1 (partially attenuated) strains, respectively, of the G2b type. The HS strain harbors a single amino acid (aa) change and two aa deletions in the N-terminal domain of S1 (⁵⁵I⁵⁶G⁵⁷E→⁵⁵K⁵⁶Δ⁵⁷Δ). The SGP-M1 strain harbors a seven aa deletion in the C-terminal domain of S2 (^1380~1386ΔFEKVHVQ). By co-infecting various animal cells with these two strains (HS and SGP-M1), we succeeded in cloning strain HSGP, which harbors the mutations present in the two original viruses. The CPE pattern of the HSGP strain was different from that of the HS and SGP-M1 strains, with higher viral titers. Studies in piglets showed attenuated pathogenicity of the HSGP strain, with no clinical symptoms or viral shedding, and histopathologic lesions similar to those in negative controls. These findings confirm that deletion of specific sequences from the S gene attenuates the pathogenicity of PEDV. In addition, HSGP strains created by combining two different strains have the potential for use as novel attenuated live vaccine candidates.

Genetic Profile of African Swine Fever Viruses Circulating at Pig Farms in South Korea during the Outbreaks between 2022 and April 2023

Fifteen pig farms were affected by African swine fever (ASF) in South Korea during the outbreaks between 2022 and April 2023. The ASF virus (ASFV) genome was directly extracted from the blood and tissue samples of 15 ASFV-positive pig farms to analyze the genetic characteristics. Phylogenetic analysis revealed that the 15 strains belonged to p72 genotype II and CD2v serogroup 8, which were the central variable region (CVR) I variants of the B602L gene. Fourteen strains were intergenic region (IGR) II variants, containing an additional tandem repeat sequence (TRS), between I73L and I329R, with the exception of one strain from an ASFV-infected pig farm reported on 22 January 2023, which was an IGR I variant. In addition, a single-nucleotide polymorphism (SNP) was detected at position 107 from the start of the IGR between A179L and A137R in six isolates. The findings of this study suggest that the sources of the virus at the pig farms from which these variants originated differed from those of other pig farms.

Phylogenetic Analysis of G and P Genotypes of Bovine Group A Rotavirus Strains Isolated from Diarrheic Vietnam Cows in 2017 and 2018

This study aimed to investigate the genetic diversity of G- and P-type bovine RVAs (BoRVAs) prevalent in Vietnam. Between 2017 and 2018, the prevalence of BoRVAs detected in diarrhea samples from 8 regions was as low as 1.9% (11/582). The prevalence of the G-type was 45.5% for G6 and 18.2% for G10; however, 36.3% remain unidentified. Interestingly, all BoRVAs were investigated as P[11], and there was no diversity within this P-type. Geographically, the G6 and G10 types were not identified in any specific area; rather, they occurred in both Northern and Southern Vietnam. G6P[11] and G10P[11], which are combined G- and P-types, were identified in 71.4% and 28.6% of BoRVA-positive samples, respectively. Phylogenetic tree analysis revealed that the G6-type detected in Vietnamese cows is similar to strains derived from China, Japan, and Korea, whereas the G10 type is closely related to the Chinese strain. In addition, the P11 strain detected in Vietnamese cows is similar to the Spanish and Chinese strains. The BoRVA-positive rate was higher in cows aged less than 2 months (3.2%, 3/94) than in those aged 2 months or more (1.6%, 8/488). In summary, we detected the presence of G6P11 and G10P11 BoVRAs on Vietnamese cow farms, and found that they were more predominant in young calves than in older cows.

Immunomodulatory effects of canine mesenchymal stem cells in an experimental atopic dermatitis model

Mesenchymal stem cells (MSCs) have the potential to differentiate into multi-lineage cells, suggesting their future applicability in regenerative medicine and biotechnology. The immunomodulatory properties of MSCs make them a promising replacement therapy in various fields of animal research including in canine atopic dermatitis (AD), a skin disease with 10-15% prevalence. We investigated the immunomodulatory effects of MSCs in an experimental canine AD model induced by Dermatophagoides farinae extract ointment. Canine adipose tissue-derived MSCs (cAT-MSCs) were differentiated into mesodermal cell lineages at the third passage. Alterations in immunomodulatory factors in control, AD, and MSC-treated AD groups were evaluated using flow cytometric analysis, enzyme-linked immunosorbent assay, and quantitative reverse transcription PCR. In the MSC-treated AD group, the number of eosinophils decreased, and the number of regulatory T cells (Tregs) increased compared to those in the AD group. In addition, the immunoglobulin E (IgE) and prostaglandin E₂ levels were reduced in the MSC-treated AD group compared to those in the AD group. Furthermore, the filaggrin, vascular endothelial growth factor, and interleukin-5 gene expression levels were relatively higher in the MSC-treated AD group than in the AD group, however, not significantly. cAT-MSCs exerted immunomodulatory effects in an AD canine model via a rebalancing of type-1 and -2 T helper cells that correlated with increased levels of Tregs, IgE, and various cytokines.

Simple and Rapid Colorimetric Detection of Canine Parainfluenza Virus 5 (Orthorubulavirus mammalis) Using a Reverse-Transcription Loop-Mediated Isothermal Amplification Assay

Despite its many advantages, a reverse-transcription loop-mediated isothermal amplification (RT-LAMP) assay has yet to be developed for canine parainfluenza virus 5 (CPIV5). In this study, a visual RT-LAMP (vRT-LAMP) assay was developed for the rapid detection of CPIV5 in clinical samples. At a constant reaction temperature of 62 °C, the assay was completed within 40 min, and the results could be directly detected with the naked eye using a hydroxynaphthol blue (HNB) metal indicator without any additional detection apparatuses. The assay specifically amplified CPIV5 RNA with a limit of detection of 10 RNA copies/reaction, which was 10-fold more sensitive than the previously reported conventional reverse-transcription polymerase chain reaction (cRT-PCR) assay and was comparable to the previously reported real-time RT-PCR (qRT-PCR) assay. In a clinical evaluation using 267 nasopharyngeal swab samples collected from hospitalized dogs with respiratory symptoms, the CPIV5 detection rate using the vRT-LAMP assay was 5.24% (14/267), which was higher than that of the cRT-PCR assay (4.49%, 12/267) and consistent with that of the qRT-PCR assay, demonstrating 100% concordance with a kappa coefficient value (95% confidence interval) of 1 (1.00-1.00). The discrepancies in the results of the assays were confirmed to be attributed to the low sensitivity of the cRT-PCR assay. Owing to the advantages of a high specificity, rapidity, and simplicity, the developed vRT-LAMP assay using an HNB metal indicator will be a valuable diagnostic tool for the detection of CPIV5 in canine clinical samples, even in resource-limited laboratories.

First Detection of Influenza D Virus Infection in Cattle and Pigs in the Republic of Korea

Influenza D virus (IDV) belongs to the Orthomyxoviridae family, which also include the influenza A, B and C virus genera. IDV was first detected and isolated in 2011 in the United States from pigs with respiratory illness. IDV circulates in mammals, including pigs, cattle, camelids, horses and small ruminants. Despite the broad host range, cattle are thought to be the natural reservoir of IDV. This virus plays a role as a causative agent of the bovine respiratory disease complex (BRDC). IDV has been identified in North America, Europe, Asia and Africa. However, there has been no information on the presence of IDV in the Republic of Korea (ROK). In this study, we investigated the presence of viral RNA and seroprevalence to IDV among cattle and pigs in the ROK in 2022. Viral RNA was surveyed by the collection and testing of 999 cattle and 2391 pig nasal swabs and lung tissues using a real-time RT-PCR assay. IDV seroprevalence was investigated by testing 742 cattle and 1627 pig sera using a hemagglutination inhibition (HI) assay. The viral RNA positive rate was 1.4% in cattle, but no viral RNA was detected in pigs. Phylogenetic analysis of the hemagglutinin-esterase-fusion (HEF) gene was further conducted for a selection of samples. All sequences belonged to the D/Yamagata/2019 lineage. The seropositivity rates were 54.7% in cattle and 1.4% in pigs. The geometric mean of the antibody titer (GMT) was 68.3 in cattle and 48.5 in pigs. This is the first report on the detection of viral RNA and antibodies to IDV in the ROK.

Control efficacy of azadirachtin on the fall armyworm, Spodoptera frugiperda (J. E. Smith) by soil drenching

The fall armyworm (FAW), Spodoptera frugiperda, is an important agricultural pest species native to the Western Hemisphere and has recently invaded to Africa and Asia. Owing to the development of pesticide resistance and environmental contamination, ecofriendly pesticides are desirable for FAW control. Azadirachtin is a plant-derived natural pesticide with low toxicity to humans and the natural environment. Azadirachtin is primarily applied by foliar spraying; however, this approach lowers the efficacy of controlling target insects owing to photodegradation and might give a harmful effect on nontarget beneficial insects. Thus, we investigated whether applying azadirachtin to soil improves FAW control and its toxicity to corn plants. Soil drainage of azadirachtin exhibited no phytotoxic effects on corn plants but significantly reduced the larval body weight and delayed the developmental period of each larval instar of FAW. Applying 10, 15, and 20 ppm azadirachtin to soil inhibited larval growth by 68%, 76%, and 91%, respectively. Furthermore, the survival rate of FAW gradually decreased when larvae were fed azadirachtin-treated corn leaves. Collectively, this is the first study suggesting the systemic efficacy of azadirachtin by soil drenching against FAW.

Development of antisense peptide-peptide nucleic acids against fluoroquinolone-resistant Escherichia coli

BACKGROUND

Fluoroquinolones (FQs) are potent and broad-spectrum antibiotics commonly used to treat MDR bacterial infections, but bacterial resistance to FQs has emerged and spread rapidly around the world. The mechanisms for FQ resistance have been revealed, including one or more mutations in FQ target genes such as DNA gyrase (gyrA) and topoisomerase IV (parC). Because therapeutic treatments for FQ-resistant bacterial infections are limited, it is necessary to develop novel antibiotic alternatives to minimize or inhibit FQ-resistant bacteria.

OBJECTIVES

To examine the bactericidal effect of antisense peptide-peptide nucleic acids (P-PNAs) that can block the expression of DNA gyrase or topoisomerase IV in FQ-resistant Escherichia coli (FRE).

METHODS

A set of antisense P-PNA conjugates with a bacterial penetration peptide were designed to inhibit the expression of gyrA and parC and were evaluated for their antibacterial activities.

RESULTS

Antisense P-PNAs, ASP-gyrA1 and ASP-parC1, targeting the translational initiation sites of their respective target genes significantly inhibited the growth of the FRE isolates. In addition, ASP-gyrA3 and ASP-parC2, which bind to the FRE-specific coding sequence within the gyrA and parC structural genes, respectively, showed selective bactericidal effects against FRE isolates.

CONCLUSIONS

Our results demonstrate the potential of targeted antisense P-PNAs as antibiotic alternatives against FQ-resistance bacteria.

Probiotics and Postbiotics as an Alternative to Antibiotics: An Emphasis on Pigs

Probiotics are being used as feed/food supplements as an alternative to antibiotics. It has been demonstrated that probiotics provide several health benefits, including preventing diarrhea, irritable bowel syndrome, and immunomodulation. Alongside probiotic bacteria-fermented foods, the different structural components, such as lipoteichoic acids, teichoic acids, peptidoglycans, and surface-layer proteins, offer several advantages. Probiotics can produce different antimicrobial components, enzymes, peptides, vitamins, and exopolysaccharides. Besides live probiotics, there has been growing interest in consuming inactivated probiotics in farm animals, including pigs. Several reports have shown that live and killed probiotics can boost immunity, modulate intestinal microbiota, improve feed efficiency and growth performance, and decrease the incidence of diarrhea, positioning them as an interesting strategy as a potential feed supplement for pigs. Therefore, effective selection and approach to the use of probiotics might provide essential features of using probiotics as an important functional feed for pigs. This review aimed to systematically investigate the potential effects of lactic acid bacteria in their live and inactivated forms on pigs.

Production of Foot-and-Mouth Disease Type O and A Vaccine Antigens on a Pilot Scale and Determination of Optimal Amount of Antigen for Monovalent Vaccines

Foot-and-mouth disease (FMD) is a highly infectious disease affecting cloven-hoofed animals and causes significant economic losses to the livestock industry. The Type O PanAsia-2 (O PA-2) vaccine strain is protective against a wide range of serotype O FMD virus (FMDV) strains in East Asia, and A22 Iraq/24/64 (A22 IRQ) is the most widely used vaccine strain in FMD vaccine antigen banks. The aim of this study was to produce antigens from O PA-2 and A22 IRQ viruses using a 100 L bioreactor and evaluate the protective efficacy of varying antigen concentrations in pigs. More than 2 μg/mL of the antigen was recovered from the O PA-2 and A22 IRQ virus-infected supernatants. Further, inactivation of O PA-2 and A22 IRQ by binary ethyleneimine revealed that the viral titers decreased below 10^-7 TCID₅₀/mL within 13 h and 9 h, respectively. The O PA-2 and A22 IRQ vaccines, containing 10 μg and 5 μg of antigen, respectively, provided protection against homologous viruses in pigs. This is the first report demonstrating that the antigens obtained from the pilot-scale production of O PA-2 and A22 IRQ are viable candidate vaccines. These results will pave the way for industrial-scale FMD vaccine production in South Korea.

A Novel Ethyl Formate Fumigation Strategy for Managing Yellow Tea Thrips (Scirtothrips dorsalis) in Greenhouse Cultivated Mangoes and Post-Harvest Fruits

The effects of climate change and shifting consumer preferences for tropical/subtropical mango fruits have accelerated their greenhouse cultivation in South Korea, which has consequently exacerbated the risk of unexpected or exotic insect pest outbreaks. This study used the pest risk analysis (PRA) of greenhouse-cultivated mangoes provided by the Animal & Plant Quarantine Agency in Korea to evaluate the potential of ethyl formate (EF) fumigation as a new pest management strategy against the yellow tea thrips (Scirtothrips dorsalis), which is considered a surrogate pest in the thrips group according to the PRA. The efficacy and phytotoxicity of EF were evaluated in greenhouse-cultivated mango tree (Irwin variety) and post-harvest mango fruit scenarios. EF efficacy ranged from 6.25 to 6.89 g∙h/m³ for lethal concentration time (LCt)₅₀ and from 17.10 to 18.18 g∙h/m³ for LCt₉₉, indicating similar efficacy across both scenarios. Application of 10 g/m³ EF for 4 h at 23 °C could effectively control S. dorsalis (100% mortality) without causing phytotoxic damage to the greenhouse-cultivated mango trees, while post-harvest mango fruit fumigation with 15 g/m³ EF for 4 h at 10 °C showed potential for complete disinfestation of S. dorsalis without compromising fruit quality.

First identification of Tyrophagus curvipenis (Acari: Acaridae) and pathogen detection in Apis mellifera colonies in the Republic of Korea

Mites of the genus Tyrophagus (Acari: Acaridae) are among the most widely distributed mites. The species in this genus cause damage to stored products and crops, and pose a threat to human health. However, the influence of Tyrophagus spp. in apiculture remains unknown. In 2022, a study focusing on the identification of Tyrophagus species within five apiaries was conducted in Chungcheongnam Province, Republic of Korea. Its specific objective was to investigate the presence of Tyrophagus mites in response to the reported high mortality of honey bee colonies in this area. Morphological identification and phylogenetic analysis using the mitochondrial gene cytochrome-c oxidase subunit 1 (CO1) confirmed for the first time the presence of the mite species Tyrophagus curvipenis in a honey bee colony in the Republic of Korea. Two honey bee pathogens were detected in the mite, a viral pathogen (deformed wing virus, DWV) and a protozoal pathogen (Trypanosoma spp.). The presence of the two honey bee pathogens in the mite suggests that this mite could contribute to the spread of related honey bee diseases. However, the direct influence of the mite T. curvipenis on honey bee health remains unknown and should be further investigated.

Assessment of Plasma Tylosin Concentrations: A Comparative Study of Immunoassay, Microbiological Assay, and Liquid Chromatography/Mass Spectrometry

Employing affordable and uncomplicated sample preparation techniques to recommend the most efficient antibacterial therapy could help reduce antibiotic-resistant bacteria. This study evaluated the suitability of immunoassays and microbiological assays as alternatives for liquid chromatography/mass spectrometry (LC/MS) in determining plasma tylosin concentrations after intramuscular administration at a dose of 20 mg/kg to both healthy and diseased pigs in clinical veterinary practice. The diseased pigs were confirmed using the target genes Actinobacillus pleuropneumoniae (apxIVA) and Pasteurella multocida (kmt1). The methods showed good linearity, precision, and accuracy. In both healthy and diseased pigs, a significant correlation was observed between LC/MS and the microbiological assay (Pearson correlation coefficient: 0.930, p < 0.001 vs. Pearson correlation coefficient: 0.950, p < 0.001) and between LC/MS and the enzyme-linked immunosorbent assay (ELISA) (Pearson correlation coefficient: 0.933; p < 0.001 vs. Pearson correlation coefficient: 0.976, p < 0.001). A strong correlation was observed between the microbiological assay and the ELISA in both healthy and diseased pigs (Pearson correlation coefficient: 0.911; p < 0.001 vs. Pearson correlation coefficient: 0.908, p < 0.001). A Bland-Altman analysis revealed good agreement between the methods, i.e., 95% of the differences were within the limits of agreement. Therefore, the microbiological assay and the ELISA, which demonstrated sufficient precision and accuracy, can be viable alternatives to LC/MS when it is unavailable.

Construction of an Agroinfectious Clone of a Korean Isolate of Sweet Potato Symptomless Virus 1 and Comparison of Its Infectivity According to Agrobacterium tumefaciens Strains in Nicotiana benthamiana

Sweet potato symptomless virus 1 (SPSMV-1) is a single-stranded circular DNA virus, belonging to the genus Mastrevirus (family Geminiviridae) that was first identified on sweet potato plants in South Korea in 2012. Although SPSMV-1 does not induce distinct symptoms in sweet potato plants, its co-infection with different sweet potato viruses is highly prevalent, and thus threatens sweet potato production in South Korea. In this study, the complete genome sequence of a Korean isolate of SPSMV-1 was obtained by Sanger sequencing of polymerase chain reaction (PCR) amplicons from sweet potato plants collected in the field (Suwon). An infectious clone of SPSMV-1 (1.1-mer) was constructed, cloned into the plant expression vector pCAMBIA1303, and agro-inoculated into Nicotiana benthamiana using three Agrobacterium tumefaciens strains (GV3101, LBA4404, and EHA105). Although no visual differences were observed between the mock and infected groups, SPSMV-1 accumulation was detected in the roots, stems, and newly produced leaves through PCR. The A. tumefaciens strain LBA4404 was the most effective at transferring the SPSMV-1 genome to N. benthamiana. We confirmed the viral replication in N. benthamiana samples through strand-specific amplification using virion-sense- and complementary-sense-specific primer sets.