Objective: The coronavirus disease 2019 (COVID-19) pandemic continues to present a major challenge to public health. Vaccine development requires an understanding of the kinetics of neutralizing antibody (NAb) responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Methods: In total, 605 serum samples from 125 COVID-19 patients (from January 1 to March 14, 2020) varying in age, sex, severity of symptoms, and presence of underlying diseases were collected, and antibody titers were measured using a micro-neutralization assay with wild-type SARS-CoV-2. Results: NAbs were detectable approximately 10 days post-onset (dpo) of symptoms and peaked at approximately 20 dpo. The NAb levels were slightly higher in young males and severe cases, while no significant difference was observed for the other classifications. In follow-up cases, the NAb titer had increased or stabilized in 18 cases, whereas it had decreased in 26 cases, and in one case NAbs were undetectable at the end of our observation. Although a decreasing trend in NAb titer was observed in many cases, the NAb level was generally still protective. Conclusion We demonstrated that NAb levels vary among all categories of COVID-19 patients. Long-term studies are needed to determine the longevity and protective efficiency of NAbs induced by SARS-CoV-2.
Adult ; Aged ; Aged, 80 and over ; Antibodies, Neutralizing/immunology* ; Antibodies, Viral/immunology* ; COVID-19/immunology* ; Female ; Humans ; Kinetics ; Male ; Middle Aged ; Neutralization Tests ; SARS-CoV-2

PURPOSE: Foot-and-mouth disease (FMD) and anthrax are important diseases in sheep. Vaccination is a favorable strategy against both infections. Simultaneous administration of vaccines does generally not impede the immune responses of each other, although there are some exceptions, and it may help reduce the labor and costs of vaccination as well as distress on animals. Although oil adjuvant FMD vaccine has been tried with live anthrax vaccine in cattle, there are no reports on the simultaneous use of both vaccines in sheep. MATERIALS AND METHODS: In this study, FMD seronegative sheep were used to investigate the impact of the simultaneous vaccination of FMD and anthrax on FMD antibody titers of sheep. Virus neutralization test and liquid phase blocking enzyme-linked immunosorbent assay were used to determine the antibody response to the FMD vaccine. RESULTS: The results demonstrated that both vaccines can be used simultaneously without any interference with the FMD response. Moreover, the simultaneous administration with anthrax vaccine had a stimulating effect on the early (day 7 post-vaccination) virus neutralization antibody response to the FMD vaccine. CONCLUSION: The simultaneous use of the FMD and anthrax vaccines did not hinder the response to the FMD vaccine in sheep.
Animals ; Anthrax Vaccines ; Anthrax ; Antibody Formation ; Cattle ; Enzyme-Linked Immunosorbent Assay ; Foot-and-Mouth Disease ; Neutralization Tests ; Sheep ; Vaccination ; Vaccines

PURPOSE: The first aim of this study was to develop a novel inactivated porcine epidemic diarrhea virus (PEDV) vaccine using the recently isolated Korean PEDV QIAP1401 strain and to evaluate its protective efficacy in growing pigs. The second was to determine the optimum adjuvant formulation of the inactivated PEDV vaccine that induces protection against viral challenge. MATERIALS AND METHODS: To generate high titers of infectious PEDV, the QIAP1401 isolate was passaged in Vero cells. The experimental vaccines were prepared from a binary ethyleneimine-inactivated QIAP1401 strain passaged sequentially 70 times (QIAP1401-p70), formulated with four commercial adjuvants, and administered twice intramuscularly to growing pigs. Challenge studies using a virulent homologous strain of PEDV QIAP1401-p11, which was passaged 11 times after isolation, were performed to assess protection against disease progression and viral shedding during the 15-day observation period. The vaccine-induced antibody responses were measured in serum samples collected at predetermined time points by indirect enzyme-linked immunosorbent assay and virus neutralization test. RESULTS: The QIAP1401-p70 strain had 42 amino acid (aa) mutations, including a 25 aa deletion, and was selected as the inactivated PEDV vaccine candidate. Although none of the pigs that received the experimental vaccines were completely protected against subsequent viral challenge, they exhibited a significantly higher immune response than did non-vaccinated control pigs. Among the vaccine groups, the highest antibody responses were observed in the pigs that received an oil-based multiphasic water/oil/water (W/O/W) emulsion adjuvanted vaccine, which delayed the onset of clinical symptoms and viral shedding. CONCLUSION: A novel inactivated PEDV vaccine formulated with a W/O/W emulsion adjuvant was both immunogenic and protective against viral challenge.
Antibody Formation ; Disease Progression ; Enzyme-Linked Immunosorbent Assay ; Neutralization Tests ; Porcine epidemic diarrhea virus ; Swine ; Vaccines ; Vero Cells ; Virus Shedding

We developed a Rapid Diagnostic Test (RDT) kit for detecting IgG/IgM antibodies against Zika virus (ZIKV) using monoclonal antibodies to the envelope (E) and non-structural protein 1 (NS1) of ZIKV. These proteins were produced using baculovirus expression vector with Sf9 cells. Monoclonal antibodies J2G7 to NS1 and J5E1 to E protein were selected and conjugated with colloidal gold to produce the Zika IgG/IgM RDT kit (Zika RDT). Comparisons with ELISA, plaque reduction neutralization test (PRNT), and PCR were done to investigate the analytical sensitivity of Zika RDT, which resulted in 100% identical results. Sensitivity and specificity of Zika RDT in a field test was determined using positive and negative samples from Brazil and Korea. The diagnostic accuracy of Zika RDT was fairly high; sensitivity and specificity for IgG was 99.0 and 99.3%, respectively, while for IgM it was 96.7 and 98.7%, respectively. Cross reaction with dengue virus was evaluated using anti-Dengue Mixed Titer Performance Panel (PVD201), in which the Zika RDT showed cross-reactions with DENV in 16.7% and 5.6% in IgG and IgM, respectively. Cross reactions were not observed with West Nile, yellow fever, and hepatitis C virus infected sera. Zika RDT kit is very simple to use, rapid to assay, and very sensitive, and highly specific. Therefore, it would serve as a choice of method for point-of-care diagnosis and large scale surveys of ZIKV infection under clinical or field conditions worldwide in endemic areas.
Antibodies ; Antibodies, Monoclonal ; Baculoviridae ; Brazil ; Cross Reactions ; Dengue Virus ; Diagnosis ; Diagnostic Tests, Routine ; Enzyme-Linked Immunosorbent Assay ; Flavivirus ; Gold Colloid ; Hepacivirus ; Immunoglobulin G ; Immunoglobulin M ; Korea ; Methods ; Neutralization Tests ; Point-of-Care Systems ; Polymerase Chain Reaction ; Reagent Kits, Diagnostic ; Sensitivity and Specificity ; Sf9 Cells ; Yellow Fever ; Zika Virus

Arthropod-borne viruses (Arboviruses) are transmitted by arthropods such as Culicoides biting midges and cause abortion, stillbirth, and congenital malformation in ruminants, apparently leading to economic losses to farmers. To monitor the distribution of Culicoides and to determine their relationship with different environmental conditions (temperature, humidity, wind speed, and altitude of the farms) on 5 cattle farms, Culicoides were collected during summer season (May-September) in 2016 and 2017, and analyzed for identification of species and detection of arboviruses. About 35% of the Culicoides were collected in July and the collection rate increased with increase in temperature and humidity. The higher altitude where the farms were located, the more Culicoides were collected on inside than outside. In antigen test of Culicoides against 5 arboviruses, only Chuzan virus (CHUV) (2.63%) was detected in 2016. The Akabane virus (AKAV), CHUV, Ibaraki virus and Bovine ephemeral fever virus (BEFV) had a positive rate of less than 1.8% in 2017. In antigen test of bovine whole blood, AKAV (12.96%) and BEFV (0.96%) were positive in only one of the farms. As a result of serum neutralization test, antibodies against AKAV were generally measured in all the farms. These results suggest that vaccination before the season in which the Culicoides are active is probably best to prevent arbovirus infections.
Agriculture ; Altitude ; Animals ; Antibodies ; Arbovirus Infections ; Arboviruses ; Arthropods ; Cattle ; Ceratopogonidae ; Ephemeral Fever Virus, Bovine ; Farmers ; Humidity ; Jeollabuk-do ; Korea ; Neutralization Tests ; Palyam Virus ; Ruminants ; Seasons ; Stillbirth ; Vaccination ; Wind

Canine adenovirus type 2 (CAV-2) is the cause of a major respiratory illness in dogs. In this study, we analyzed adenovirus infections in dogs using 2000–2017 data from the Animal and Plant Quarantine Agency (APQA) and conducted a serological survey of CAV-2 infection in six animal species in Korea. In total, 38 of the 3,179 dog samples were confirmed as canine adenovirus infections. In serological survey, 1,028 dog sera, 160 raccoon dog sera, 100 cattle sera, 257 sow sera, 206 horse sera, and 106 cat sera, collected from January 2016 to July 2018, were screened for the presence of anti-CAV-2 antibodies by virus neutralization test. The seropositivity rates for dogs, raccoon dogs, cattle, sows, horses, and cats were 88.5% (910/1,028), 51.3% (82/160), 85.0% (85/100), 48.6% (125/257), 35.0% (72/206), and 2.8% (3/106), respectively. Among dogs and raccoon dogs, 1.9% (20/1,028) and 8.8% (14/160), respectively, had a virus-neutralizing antibody (VNA) titer of over 1:256. A high CAV-2 VNA titer indicates a repeated vaccination or natural infection in Korean dogs and circulation of CAV-2 in raccoon dog populations.
Adenoviridae Infections ; Adenoviruses, Canine* ; Animals* ; Antibodies ; Cats ; Cattle ; Dogs ; Horses ; Incidence* ; Korea ; Neutralization Tests ; Plants ; Quarantine ; Raccoon Dogs ; Vaccination

Swine vesicular disease (SVD) is a highly contagious viral disease that causes vesicular disease in pigs. The importance of the disease is due to its indistinguishable clinical signs from those of foot-and-mouth disease, which prevents international trade of swine and related products. SVD-specific antibody detection via an enzyme-linked immunosorbent assay (ELISA) is the most versatile and commonly used method for SVD surveillance and export certification. Inactivated SVD virus is the commonly used antigen in SVD-related ELISA. A recombinant SVD virus-like particle (VLP) was generated by using a Bac-to-Bac baculovirus expression system. Results of SVD-VLP analyses from electron microscopy, western blotting, immunofluorescent assay, and mass spectrometry showed that the recombinant SVD-VLP morphologically resemble authentic SVD viruses. The SVD-VLP was evaluated as a replacement for inactivated whole SVD virus in competitive and isotype-specific ELISAs for the detection of antibodies against SVD virus. The recombinant SVD-VLP assay produced results similar to those from inactivated whole virus antigen ELISA. The VLP-based ELISA results were comparable to those from the virus neutralization test for antibody detection in pigs experimentally inoculated with SVD virus. Use of the recombinant SVD-VLP is a safe and valuable alternative to using SVD virus antigen in diagnostic assays.
Animals ; Antibodies ; Baculoviridae ; Blotting, Western ; Certification ; Enterovirus B, Human ; Enzyme-Linked Immunosorbent Assay ; Foot-and-Mouth Disease ; Mass Spectrometry ; Methods ; Microscopy, Electron ; Neutralization Tests ; Serologic Tests* ; Swine Vesicular Disease* ; Swine* ; Virus Diseases

Foot-and-mouth disease is one of the most important viral diseases of cloven-hoofed animals. Mass vaccination is an effective method to control the disease and is frequently utilized in endemic regions. Sufficient protection of young animals is important in mass vaccination campaigns. Maternal antibodies negatively affect the success of vaccination. Hence, determination of the optimal vaccination age is crucial for the uninterrupted protection of young animals. This study was performed to identify the effect of vaccine potency and booster administration on serum neutralizing antibody titers of calves with different levels of maternal antibodies. Calves (n = 111) on a state farm were used in this study. Oil adjuvant foot-and-mouth disease vaccines with 3 PD₅₀ and 6 PD₅₀ potencies were used with or without booster administration. Serum samples were collected each month up to day 120 postvaccination. Virus neutralization tests were used to measure the serum neutralizing antibody titers and estimate the protection period by using pre-determined cut-off values for protection. The results revealed that a vaccination with a 6 PD₅₀ potency vaccine, preferably followed by a booster dose, should be used to overcome maternal immunity for incessant protection.
Agriculture ; Animals ; Antibodies* ; Antibodies, Neutralizing ; Antibody Formation* ; Foot-and-Mouth Disease* ; Mass Vaccination ; Methods ; Neutralization Tests ; Vaccination ; Vaccine Potency* ; Vaccines* ; Virus Diseases

Japanese encephalitis (JE) is an important zoonosis caused by the mosquito-transmitted JE virus (JEV), which is a causative agent of reproductive failure in pregnant sows. Detection of JEV antibodies in swine is performed by hemagglutination inhibition (HI), virus neutralization (VN), and the plaque reduction neutralization test (PRNT). The most stringent PRNT is the 90% endpoint PRNT (PRNT₉₀). These conventional assays are difficult to carry out in diagnostic laboratories with insufficient instruments or cell culture systems. An alternative assay that is easily conducted and time efficient is required. In this study, we improved the indirect enzyme-linked immunosorbent assay (I-ELISA) with clarified antigen for the detection of JEV antibodies. The I-ELISA results obtained from 175 swine serum samples were compared with HI, VN, and PRNT₉₀ results. The sensitivity of I-ELISA was 91.8%, 95.0%, and 94.7% compared with HI, VN, and PRNT₉₀ results, respectively. The specificity of I-ELISA was 92.2%, 94.7%, and 94.7% compared with HI, VN, and PRNT₉₀ results, respectively. Moreover, the I-ELISA results were significantly correlated with the HI (r = 0.93), VN (r = 0.95), and PRNT₉₀ (r = 0.92) results. These results suggest that the improved I-ELISA is useful for serosurveillance of JEV in swine.
Antibodies ; Asian Continental Ancestry Group* ; Cell Culture Techniques ; Encephalitis Virus, Japanese* ; Encephalitis, Japanese* ; Enzyme-Linked Immunosorbent Assay* ; Hemagglutination ; Humans ; Neutralization Tests ; Sensitivity and Specificity ; Swine*

Severe fever with thrombocytopenia syndrome (SFTS) is caused by the SFTS virus (SFTSV). The SFTSV appears to have a wide host range, as SFTSV-positive ticks have been isolated from both farm animals and wild rodents. Therefore, it is important to monitor SFTSV-positive animals to prevent the transmission of SFTSV from animals to humans. Previously, we developed a competitive enzyme-linked immunosorbent assay (cELISA) to detect SFTSV-specific antibodies from field animals and compared the cELISA results to those from an indirect immunofluorescence assay (IFA). In this study, cELISA results were compared to and evaluated against the results from both an IFA and a virus neutralization (VN) test of 193 bovine serum samples (including two bovine positive control sera) and 70 horse serum samples. The consistency (98.9%) between cELISA and VN results was higher than that (97.4%) between cELISA and IFA for the bovine serum samples. Similarly, for the horse serum samples, the consistency (88.6%) between cELISA and VN results was higher than that (84.3%) between the cELISA and IFA. These findings indicate that our newly developed cELISA can be used for surveillance or epidemiological studies of SFTSV in animals.
Animals ; Animals, Domestic ; Antibodies ; Enzyme-Linked Immunosorbent Assay* ; Epidemiologic Studies ; Fever* ; Fluorescent Antibody Technique, Indirect ; Horses ; Host Specificity ; Humans ; Neutralization Tests* ; Rodentia ; Thrombocytopenia* ; Ticks