Dong-Wan Kim

Foot-and-mouth disease virus serotype O remains a global threat, particularly the O/CATHAY topotype in East and Southeast Asia. Because timely access to emerging field isolates can be limited, reverse genetics provides a flexible approach for generating viruses representing selected circulating strains for vaccine matching and efficacy evaluation. Here, we generated O/CATH/APQA-V18 and evaluated its suitability for vaccine assessment in pigs. A contemporary Vietnamese O/CATHAY strain was selected based on viral protein-1 phylogenetic analysis, and its P1 capsid-coding region was incorporated into an O1 Manisa backbone using reverse genetics. The recombinant virus was characterized by real-time reverse transcription polymerase chain reaction, transmission electron microscopy, and sequence analysis. Two-dimensional virus neutralization tests using sera against O/PanAsia-2 and O/Primorsky yielded antigenic relationship values of 0.04 and 0.11, respectively, indicating poor antigenic matching. In vivo, O/CATH/APQA-V18 induced clinical signs in unvaccinated pigs, confirming its infectivity and pathogenicity. Vaccinated pigs had low neutralizing antibody titers against O/CATH/APQA-V18 before challenge, and only 25% were protected. These findings support O/CATH/APQA-V18 as a genetically defined and reproducible experimental virus for vaccine matching and protective efficacy evaluation against contemporary O/CATHAY viruses.

Foot-and-mouth disease (FMD) is a highly contagious viral disease that seriously threatens livestock health. Protective immunity induced by vaccination is primarily associated with the generation of neutralizing antibodies; however, conventional virus neutralization tests are time-consuming and require the handling of live virus, limiting their suitability for rapid and repeated evaluation in routine settings. In this study, we established a surrogate neutralization assay for the functional evaluation of neutralizing antibody activity against FMD virus (FMDV) serotype O. The assay measures changes in luciferase-based luminescent signals generated following exposure of LgBiT-expressing cells to HiBiT-tagged virus-like particle (VLP) preparations. FMDV serotype O-derived VLPs exhibited stable capsid protein expression, assembly characteristics, and morphological integrity similar to those of virus particles, as confirmed by sucrose gradient fractionation and electron microscopy. In the presence of neutralizing antibodies, a reduction in luminescent signals was observed, enabling functional discrimination of antibody activity. The surrogate assay results showed a strong correlation with those of the conventional virus neutralization test for FMDV serotype O (R² = 0.9068). This study demonstrates the feasibility of the surrogate neutralization assay for assessing the functional activity of neutralizing antibodies and its potential applicability to vaccine immunogenicity assessment and functional antibody analysis.

Background: Foot-and-mouth disease (FMD) is a highly contagious viral disease causing substantial economic losses in livestock. Conventional intramuscular (IM) vaccination is widely used for FMD control but may be associated with transient reductions in milk production. This study evaluated whether intradermal (ID) vaccination could induce comparable immune responses and protection while minimizing potential impacts on productivity. Methods: In cattle, the immunogenicity of an experimental bivalent ID vaccine was compared with that of a commercially available IM vaccine by measuring antibody responses for up to 140 days post-vaccination (dpv). Milk production was monitored for 7 dpv in a separate cohort of lactating cattle. Protective efficacy was evaluated in goats following ID vaccination and challenge with a 2025 Republic of Korea serotype O field isolate (O/ME-SA/Ind-2001). Results: ID vaccination induced humoral immune responses comparable to those elicited by IM vaccination throughout the 140-day observation period. Although no statistically significant difference in milk production was observed, the ID group showed a smaller numerical reduction in milk yield. Following viral challenge, ID-vaccinated goats developed rapid neutralizing antibody responses, exhibited no clinical signs, and showed lower viral RNA levels than unvaccinated controls. Conclusions: Intradermal vaccination induced long-lasting immune responses comparable to conventional IM vaccination, was associated with a smaller numerical reduction in milk yield, and protected goats against challenge with a contemporary FMDV field isolate. These findings provide preliminary evidence supporting the potential of ID vaccination as an alternative strategy for FMD control in ruminants and warrant further comparative studies with conventional IM vaccination.

Background: In South Korea, foot-and-mouth disease (FMD), a highly contagious viral infection that affects cloven-hoofed animals, has led to the implementation of a bivalent FMD vaccination program. The current FMD vaccination strategy involves intramuscular (IM) administration to the shoulder region of the swine. However, this method is associated with adverse reactions at injection sites. Our previous studies have demonstrated that intradermal (ID) vaccination eliminates these side effects while maintaining immunogenicity comparable to that of IM vaccination. This study aimed to assess the early immune response induced by ID vaccination and compare its protective ability against FMDV serotype O with that of a commercial IM vaccine recently used in South Korea. Methods: An ID FMD vaccine was evaluated using two adjuvants, ISA 207 (50%) and EMULSIGEN-D (15%). Virus neutralization (VN) titers and structural protein levels were measured to compare efficacy across groups. To assess the early protective efficacy of ID vaccination, viral challenge experiments were conducted at 7 and 14 days post-vaccination (dpv). Results: Swine vaccinated via the ID route exhibited no clinical symptoms at 14 dpv, indicating effective early protection against FMD (O/AS/SKR/2019). In addition, no side effects of FMD ID vaccination were observed. Conclusions: These results suggest that ID vaccination could serve as a viable alternative to conventional IM vaccination, which is frequently associated with adverse effects. Importantly, this study demonstrates that ID vaccination can provide effective early protection within 7–14 days post-vaccination, highlighting its potential utility for emergency outbreak control.

The world is divided into seven regional pools based on the serotype distribution and geographical spread of the foot-and-mouth disease (FMD) virus. The Republic of Korea (ROK) belongs to Pool 1, where serotypes O, A, and Asia1 are endemic. Recently, the risk of incursions by the O/CATHAY topotype has increased in Pool 1, raising concerns about its potential introduction into the ROK. To assess the protective effectiveness of three commercial FMD vaccine strains—O1/Manisa + O/3039, O/Primorsky, and O1/Campos—currently used in the ROK against this topotype, an animal challenge experiment was conducted. Three treatment groups (n = 4 in each) of pigs received a single 2 mL injection of one of the vaccines at 8–10 weeks of age, and the other group (n = 2) served as the control. All pigs were challenged with the O/HKN/5/2019 virus (O/CATHAY topotype) at 21 days post-vaccination. All vaccines conferred protective effects, with O1/Campos demonstrating the highest efficacy by inducing fewest clinical signs and significantly reducing virus shedding in the treated groups compared with those in the control group. These findings suggest O1/Campos may serve as an emergency measure; nevertheless, the development of a vaccine specifically targeting the O/CATHAY topotype is warranted.

Background/Objectives: Foot-and-mouth disease (FMD) is a highly contagious class 1 animal disease that affects cloven-hoofed animals, such as cattle, pigs, and goats. Diagnosis and research on live FMD virus (FMDV) typically require biosafety level 3 facilities, which are challenging to maintain due to strict protocols and high costs. The development of NanoBiT-based assays has accelerated in response to the coronavirus disease pandemic, providing safer alternatives for viral research, and is now applicable for general laboratories. This study aimed to develop a NanoBiT-based virus-like particle (VLP) assay for the rapid and safe screening of neutralizing antibodies against FMDV Asia1 Shamir (AS). Methods: We developed an AS VLP with an inserted HiBiT tag that enabled the detection of entry into LgBiT cells through luminescence signals. Results: HiBiT-tagged AS VLPs mixed with anti-serum and introduced into LgBiT-expressing cells led to a reduction in luciferase activity. Therefore, we established a NanoBiT-based viral neutralizing antibody test (VNT) that demonstrated a high correlation (R² = 0.881) with the traditional gold standard VNT. Conclusions: The assay demonstrated high sensitivity and could be performed in BL-2 facilities, offering a safer and more efficient alternative to traditional assays while reducing the need to handle live viruses in high-containment facilities. This method provides a valuable tool for rapid screening of neutralizing antibodies and can be adapted for broader applications in FMDV research.

In South Korea, a mandatory nation-wide foot-and-mouth disease (FMD) vaccination policy is in place. However, a major side effect of the current method of intramuscular (IM) administration of oil-adjuvanted FMD vaccines is the formation of granulomas in the muscles of pigs. To address this issue, we assessed the possible application of intradermal (ID) vaccination. Initially, we compared the serological immune response in specific pathogen-free pigs inoculated with FMD vaccines formulated with eight different adjuvants, administered twice at the neck site using a syringe with a needle via the ID route. Among the formulations (water-in-oil-in-water (W/O/W), oil-in-water (O/W), and polymer nanomaterials), ISA 207 of W/O/W was the most effective in inducing immunogenicity followed by ISA 201 of W/O/W. ISA 207 was further tested in formulations of different antigen doses (12 or 1.2 μg) delivered via both IM and ID routes. All four treatments successfully protected the pigs against FMD virus challenges. To assess the feasibility of the field application of the vaccines with ISA 207, we conducted ID vaccination of conventional pigs using a needle-free device, resulting in the detection of significant levels of neutralizing antibodies. ISA 207 was shown to be superior to ISA 201 in inducing immunogenicity via the ID route. In conclusion, ISA 207 could be a suitable adjuvant for ID vaccination in terms of vaccine efficacy for FMD, allowing for alternate use of ID vaccination and subsequent reduction in the incidences of granuloma formation in the field.

Foot-and-mouth disease virus (FMDV) is a highly contagious virus that affects cloven-hoofed animals and causes severe economic losses in the livestock industry. Given that this high-risk pathogen has to be handled in a biosafety level (BSL)-3 facility for safety reasons and the limited availability of BSL-3 laboratories, experiments on FMDV call for more attention. Therefore, we aimed to develop an FMDV experimental model that can be handled in BSL-2 laboratories. The NanoBiT luciferase (Nano-luc) assay is a well-known assay for studying protein–protein interactions. To apply the NanoBiT split luciferase assay to the diagnosis and evaluation of FMD, we developed an inactivated HiBiT-tagged Asia1 Shamir FMDV (AS-HiBiT), a recombinant Asia1 shamir FMDV with HiBiT attached to the VP1 region of Asia1 shamir FMDV. In addition, we established LgBiT-expressing LF-BK cell lines, termed LgBit-LF-BK cells. It was confirmed that inactivated AS-HiBiT infected LgBiT-LF-BK cells and produced a luminescence signal by binding to the intracellular LgBiT of LgBiT-LF-BK cells. In addition, the luminescence signal became stronger as the number of LgBiT-LF-BK cells increased or the concentration of inactivated AS-HiBiT increased. Moreover, we confirmed that inactivated AS-HiBiT can detect seroconversion in sera positive for FMDV-neutralizing antibodies. This NanoBiT split luciferase assay system can be used for the diagnosis and evaluation of FMD and expanded to FMD-like virus models to facilitate the evaluation of FMDV vaccines and antibodies.

Following the worst outbreak of foot-and-mouth disease (FMD), a highly contagious disease in cloven-hoofed animals caused by the FMD virus, from November 2010–April 2011, the Korean government enforced a mandatory vaccination policy. A bivalent (FMD type O and A; O + A) vaccine has been recently implemented. Although the FMD outbreak was suppressed by vaccination, the intramuscular (IM) injection presents side effects. Therefore, improving FMD vaccine quality is necessary. Here, we investigated the side effects and immune efficacy of the O + A bivalent vaccine using two different routes of administration: intradermal (ID) and IM. To compare the immune efficacy of the two inoculation routes, virus neutralization titers and structural protein (antigen) levels were measured. The protective efficacy of ID vaccines was confirmed using two viruses (FMDV O/AS/SKR/2019 and A/GP/SKR/2018) isolated in the Republic of Korea. Serological analysis revealed that both animals administered by ID and IM injections exhibited equal immune efficacy. A virus challenge test in the target animal (swine) revealed no (or extremely low) clinical symptoms. Swine in the ID injected group exhibited no side effects. In conclusion, we suggest that the ID route of vaccination is an effective alternative to the existing IM route, which is associated with more frequent side effects.