Canine parvovirus-2 (CPV-2) has been reported worldwide as a major pathogen associated with acute hemorrhagic enteritis. The disease is a major infectious cause of death, particularly in young dogs. The earliest type of CPV-2 was replaced with three main subspecies, CPV-2a, CPV-2b, and CPV-2c, within a few years. Vaccination is carried out regularly, but the emergence of antigenic variants and the influence of maternal antibodies have limited the efficacy of commercial vaccines. New vaccines, such as the subunit vaccine, have been developed for alternative, safe, and effective vaccination. The baculovirus expression vector system (BEVS) is an excellent eukaryotic expression system with a high-level expression of foreign proteins and the ability of post-translational modification. Therefore, it is used widely to produce recombinant protein and subunit vaccines. In this study, the VP2 protein of CPV-2b cloned in the gateway vector system was generated using a baculovirus expression system in Spodoptera frugiperda (SF9) insect cells. Hemagglutination assay (HA) titers (24) were obtained, and the expression was detected in 6-His tagged VP2 and monoclonal antibody (mAb) against CPV-2 by western blotting. The VP2 protein of CPV-2b expressed in this study may provide a basis for a clinical diagnosis and vaccination applications for CPV-2.

Influenza A viruses (IAVs) are members of the family Orthomyxoviridae and genus Orthomyxovirus. Avian and mammalian species are the host of IAVs, which includes humans and dogs. Canine influenza virus (CIV) is an emerging pathogen that causes severe and acute respiratory diseases in dogs. This study monitored the antigen and antibody against CIV in dogs in the Republic of Korea (ROK) from 2016 to 2021. One thousand and seventy-two nasal swabs and 1,545 blood samples were collected from animal hospitals and animal shelters. Five nasal swabs in 2017 and seven in 2018 from stray dogs were positive for CIV according to RT-PCR. The prevalence of H3N2 CIV ranged from 9.5% to 24.8%, according to the hemagglutination inhibition (HI) assay. On the other hand, none of the serum samples from 2018 to 2021 showed seropositivity against the avian H5, H7, and H9 viruses. The HI titers for H3N2 ranged from 16 to 512. The distribution of HI titer 16–32 was 57.6% in seropositive samples. The pet dogs were vaccinated against CIV, but the stray and military dogs were unvaccinated. In 2017 and 2018, the seroprevalence of CIV in stray dogs was higher than in the other years, and viral RNA was detected in nasal swabs. It may mean previous exposure of stray dogs to CIV. With the increasing number of pet dogs and the close contact between humans and dogs, canines could serve as an intermediate host for transmitting IAVs to humans. Therefore, continuous surveillance of CIV is needed for public health and the potential emergence of novel zoonotic viruses.

The canine parvovirus (CPV) causes clinical signs, such as severe enteritis, dehydration, diarrhea, vomiting, leukopenia, and hair loss, which may lead to death. Vaccination is still the most important approach, as no specific treatment exists to prevent CPV. Monoclonal antibodies are valuable tools to study the pathogenic mechanisms of CPV and develop effective diagnostic reagents and pharmaceuticals. In this study, two monoclonal antibodies (MAbs) against CPV-2a were obtained through hybridoma technology by fusing myeloma cells and B cells from the spleens of mice immunized with CPV type 2a (CPV-2a). Two MAbs (CPV-330 and CPV-620) were studied on the reactivity of vaccine (CPV-2a) and field strains (CPV-new 2a, -2b, and -2c) by indirect immunofluorescence (IFA), hemagglutination inhibition test (HI), virus neutralization test (VN), and inhibition of virus growth test. Two MAbs showed similar antibody titers for HI and VN. On the other hand, CPV-330 inhibited the viral replication in Crandell-Rees Feline Kidney (CRFK) cells better than CPV-620. These CPV MAbs may provide valuable biological reagents to study the CPV pathogenic mechanisms and work as therapeutic antibodies.

In this study, the near-complete genome sequence of the novel reassortant H1N2 influenza A virus strain A/swine/Korea/KS60/2016 is reported. Sequences of the hemagglutinin (HA), neuraminidase (NA), and polymerase basic 2 (PB2) genes were analyzed, revealing that the isolates contain segments from previous Korean swine H1N2 strains. Additionally, the remaining genes of this strain originated from human H1N1 strains in 2009.

Canine parvovirus (CPV) remains a leading infectious cause of death in canines, especially in young puppies. Though vaccination is being carried out regularly, immunization failures occur, and puppies may be exposed to infection. Virus-like particles (VLPs) act like a subunit vaccine, mimicking the structure of authentic viruses. Therefore, VLPs have the potential to be used as vaccine candidates. Since Viral Protein 2 (VP2), a major structural protein of CPV, is the crucial antigen for CPV, the purpose of this study was to produce a recombinant VP2 of new canine parvovirus-2a using the baculovirus expression system in SF9 insect cells. The results revealed that recombinant VP2 assembles to form VLPs with antigenic properties similar to those of natural CPV, the recombinant VLP can produce a hemagglutination assay (HA) titer (1:210) in SF9 cells. Expression of the recombinant 6-His-tagged VP2 in SF9 cells was confirmed by western blotting. These findings suggest that the recombinant VP2 expressed in this study could be used as an efficient subunit vaccine against CPV infection.

Influenza A virus (IAV) causes respiratory disease in birds and mammals, including pigs and humans. Infection by IAV in pigs increases not only economic losses in the swine industry but also the emergence of novel IAV variants via gene reassortment, which is important due to the susceptibility of both birds and humans to IAV. This study provides serological data obtained during a study to detect IAV infections in pigs in the Republic of Korea during 2018 and 2019. A total of 1,559 samples were collected from 74 domestic pig farms. Hemagglutination inhibition (HI) assays were performed using the A/Swine/Korea/25-13(H1N1), A/Swine/Korea/E102 (H1N2), and A/Swine/Korea/Cy10/2007 (H3N2) viruses as antigens. The HI assay results showed that 266 of the 1,559 samples were seropositive (17.0%). Among these, H1N1, H1N2, and H3N2 comprised 7.3% (114), 6.0% (93), and 8.8% (137) of the 1,559 samples, respectively. Co-infections of H1N1/H1N2, H1N1/H3N2, H1N2/H3N2 and H1N1/H1N2/H3N2 were observed in 2.1% (31), 1.5% (23), 1.5% (24), and 0.8% (13) of the 1,559 samples, respectively. Interestingly, IAV infections were detected in all nine provinces of the country.

In this study, antibody responses after vaccination against equine influenza were investigated among 1,591 horses in the Republic of Korea using the hemagglutination inhibition (HI) test. Equine influenza has not occurred since 2011 and a commercial vaccine against H3N8 has been used. The equine influenza virus, A/equine/South Africa/4/03 (H3N8), was used as the antigen in the HI assay. The mean seropositive rate was 90.5% in 2019. Except for stallion whose seropositive rate was 78.5%, all seropositive rates of other horse types were over 90%. Regionally, except for Gangwon-do and Jeju-do whose seropositive rates were 89.0% and 87.1%, all seropositive rates in other provinces were over 90%. In the future, more through vaccination against equine influenza needs to be done based on this investigation result.

Viral protein 2 (VP2), which is the structural protein of parvovirus, can produce virus-like particles (VLPs) by a self-assembly process in vitro, making VLPs attractive vaccine candidates. VP2 of canine parvovirus (CPV) is responsible for neutralizing antibodies in immunized animals. In this study, VP2 protein of canine parvovirus-2c was expressed using a baculovirus expression system and assembled into parvovirus-like particles in insect cells. The results show that VP2 proteins assembled into virus-like particles (VLPs) with antigenic properties similar to those of natural CPV and a high hemagglutination (HA) titer (1:27). The recombinant 6-His-tagged VP2 protein with a molecular mass of about 65 kDa was detected by anti-His antibody and anti-PPV serum. This study provides a foundation for the application of VP2 protein in the clinical diagnosis of CPV and in the vaccination against CPV.

Viral protein 2 (VP2) of porcine parvovirus (PPV) is responsible for inducing neutralizing antibodies in immunized animals. It is the major viral structural protein. In this study, novel subunit vaccines against PPV based on virus-like particles (VLPs) formed from VP2 proteins (PPV 13-7 Korean strain) were expressed in an insect baculovirus cell system and purified using Ni-NTA affinity column chromatography. These VP2 proteins assembled into virus-like particles (VLPs). They showed antigenic properties similar to those of natural PPV. In addition, they showed high hemagglutination (HA) titers (211 for PPV 13-7 Korean strain). This study provides a foundation for the application of the difference immunization of recombinant protein in the diversity of PPV VP2 genes and in vaccination against PPV in the future.

Canine parvovirus type-2 (CPV-2) has been reported worldwide as the main agent associated with acute hemorrhagic enteritis, resulting in high morbidity, especially in young dogs. CPV-2 has three genetic variants, 2a, 2b, and 2c. Here, we report three cases of canine parvovirus enteritis associated with CPV-2a (2 samples) and -2c (1 sample) infections that occurred in three young dogs suffering from enteritis. Isolates from dog diarrheic fecal samples were sequenced by polymerase chain reaction (PCR) and identified as two types of CPV-2a and one type of CPV-2c. This work constitutes the first isolation and genetic characterization of CPV-2c in the Republic of Korea.

Ruminant pestiviruses of bovine viral diarrhea virus (BVDV) and border disease virus (BDV) are closely related to classical swine fever virus (CSFV) and all belong to the genus of Pestiviruses. BVDV is one of the most important viral pathogen of cattle and has been recorded in most countries where cattle are raised. Natural host for BVDV is cattle, but BVDV is able to infect pigs as well. The purpose of this study was to investigate the prevalence for antibodies against BVDV in domestic pig farms in South Korea from 2009 to 2011. In this study, 2,755 pigs in 239 farms in South Korea's inland and 5,293 pigs in 613 farms in Jeju province (CSF free region) were investigated for antibodies against two pestiviruses, BVDV and CSFV by a virus neutralization test (VNT). The seroprevalences on the individual level and on herd level against BVDV were 5.3 % and 21.2 % in South Korea's inland, 5.2 % and 6.5 % in Jeju province, respectively. Based on the ratio of respective antibody titers by the comparative VNT, 273 pigs in Jeju province with BVDV infection were detected and they were distinctly negative to CSF. It is recognized that porcine infections with BVDV naturally occurred in Jeju province. Whereas, antibody titers against BVDV of South Korea's inland were cross-reactivity with CSFV.