Quang Lam Truong

African swine fever (ASF) is a highly contagious and often fatal disease of swine that causes substantial economic losses worldwide. Despite extensive efforts, the lack of safe and effective vaccines remains a major obstacle to ASF control. We previously developed a cell-adapted live-attenuated virus (LAV) vaccine candidate, VNUA-ASFV-LAV2, through serial passage of a highly virulent genotype II ASF virus (ASFV) in cell culture. VNUA-ASFV-LAV2 demonstrated favorable safety and protective efficacy against contemporary epidemic genotype II ASFV. In this study, we systematically evaluated antibody responses in pigs immunized with VNUA-ASFV-LAV2. Fourteen indirect ELISAs were developed using ASFV structural, nonstructural, and previously uncharacterized proteins associated with the viral outer envelope, capsid, inner envelope, and replication functions. Serum samples collected from vaccinated and challenged pigs were used to assess the performance of these assays. The results demonstrated that p17-, p22-, p30-, pE199L-, and pB602L-based ELISAs have strong potential for monitoring antibody responses in pigs vaccinated with VNUA-ASFV-LAV2. Among these assays, p22- and p30-based ELISAs enabled early detection of ASFV-specific antibodies in both vaccinated (as early as 7–14 days post vaccination) and wild-type ASFV-infected pigs (17 days post infection). Notably, the pF317L-based ELISA showed potential to differentiate wild-type ASFV-infected pigs from VNUA-ASFV-LAV2-vaccinated pigs. Further diagnostic validation using larger, independently characterized serum panels representing diverse ASFV strains, vaccination statuses, and epidemiological settings is needed to establish its sensitivity, specificity, reproducibility, and diagnostic accuracy. These findings provide the first comprehensive analysis of humoral immune responses elicited by VNUA-ASFV-LAV2 in pigs and identify potential serological markers for vaccine monitoring and DIVA surveillance, supporting future field applications and commercialization of this vaccine candidate.

Background and Aim: Avian pathogenic Escherichia coli (APEC), a major cause of colibacillosis in poultry, possesses diverse virulence-associated genes (VAGs) that contribute to extraintestinal pathogenicity. However, comprehensive information on VAG combinations and co-occurrence patterns among APEC isolates in Vietnam remains limited. This study aimed to characterize VAG prevalence, combination profiles, and co-occurrence patterns in APEC and non-pathogenic E. coli (NPEC) isolates from chickens in northern Vietnam. Materials and Methods: From August 2023 to August 2025, 515 spleen samples were collected from healthy and non-healthy chickens on 35 commercial poultry farms in Hanoi, Hai Phong, Phu Tho, Bac Ninh, and Thai Nguyen. A total of 200 E. coli isolates were recovered and screened by multiplex polymerase chain reaction for 19 VAGs: fimC, eaeA, papC, tsh, sfa_foc, iucD, iutA, irp2, fyuA, iucA, iroN, vat, hlyA, hlyF, astA, ompT, iss, cva/cvi, and colV. Isolates carrying ≥5 of nine selected APEC-associated VAGs were classified as APEC; the remainder were classified as NPEC. We compared gene prevalence, combination profiles, and pairwise co-occurrence using appropriate statistical tests and Jaccard similarity analysis. Results: Among 200 isolates, 121 (60.5%) were classified as APEC and 79 (39.5%) as NPEC. APEC isolates most frequently carried hlyF (100%), fimC and iutA (96.7% each), ompT and iucD (95.9% each), iss (90.1%), irp2 (79.3%), and iroN (65.3%). APEC isolates contained up to 19 VAGs, whereas NPEC isolates contained up to 14. Twenty-three distinct VAG combination profiles were identified among APEC isolates, and 103/121 (85.1%) harbored >8 VAGs. In contrast, NPEC isolates displayed 13 less complex profiles containing 3–6 VAGs. Most VAGs were significantly more prevalent in APEC than in NPEC isolates, while papC, fyuA, and eaeA occurred exclusively in APEC. Co-occurrence analyses demonstrated greater complexity and stronger VAG associations among APEC isolates. Conclusion: APEC isolates from northern Vietnam exhibited extensive VAG diversity and complex co-occurrence patterns distinct from those of NPEC isolates. These findings provide a molecular basis for improved APEC characterization, epidemiological surveillance, and targeted control of poultry colibacillosis. Keywords: avian pathogenic Escherichia coli, chickens, colibacillosis, gene co-occurrence, northern Vietnam, poultry, virulence-associated genes, virulence profiles.

African swine fever (ASF) is a highly contagious and often fatal disease of swine that causes substantial economic losses worldwide. Despite extensive efforts, the lack of safe and effective vaccines remains a major obstacle to ASF control. We previously de-veloped a cell-adapted live-attenuated virus (LAV) vaccine candidate, VNUA-ASFV-LAV2, through serial passage of a highly virulent genotype II ASF virus (ASFV) in cell culture. VNUA-ASFV-LAV2 demonstrated favorable safety and protec-tive efficacy against contemporary pandemic genotype II ASFV. In this study, we sys-tematically evaluated antibody responses in pigs immunized with VNUA-ASFV-LAV2. Fourteen indirect ELISAs were developed using ASFV structural, nonstructural, and previously uncharacterized proteins associated with the viral outer envelope, capsid, inner envelope, and replication functions. Serum samples collected from vaccinated and challenged pigs were used to assess the performance of these assays. The results de-monetarized that p17-, p22-, p30-, pE199L-, and pB602L-based ELISAs have strong po-tential for monitoring antibody responses in pigs vaccinated with VNUA-ASFV-LAV2. Among these assays, p22- and p30-based ELISAs enabled early detection of ASFV-specific antibodies in both vaccinated (as early as 7-14 days post vaccination) and wild-type ASFV infected pigs (17 days post infection). Notably, the pF317L-based ELISA successfully differentiated wild-type ASFV-infected pigs from VNUA-ASFV-LAV2-vaccinated pigs, demonstrating its potential as a DIVA-compatible diagnostic assay. These findings provide the first comprehensive analysis of humoral immune responses elicited by VNUA-ASFV-LAV2 in pigs and identify promising se-rological targets for vaccine monitoring and DIVA-based surveillance, supporting the future field application and commercialization of this vaccine candidate.

African swine fever (ASF), a highly contagious and lethal viral disease, continues to devastate the global swine industry. The emergence of ASF virus (ASFV) variants with varying genomic deletions poses significant challenges for ASF control. This study presents a novel, sensitive, and reliable quadplex real-time PCR assay for detecting ASFV variants lacking key genes (I177L, EP402R, and MGF360-14L), either individually or in combination. The assay targets conserved regions within these genes, ensuring broad coverage of diverse ASFV genotypes. A porcine beta-actin (ACTB) internal control was incorporated to minimize false-negative results. Optimization and evaluation using spike-in tests demonstrated high sensitivity, with a limit of detection (LOD) ranging from 1 to 10 plasmid copies or 0.1 TCID₅₀ of ASFV isolates per reaction. No cross-reactivity was observed when testing serum samples from pigs infected with other common swine viruses. Further validation across a diverse panel of samples, including those from naturally ASFV-infected field pigs (n = 54), experimentally ASFV-infected pigs (n = 50), PBS-inoculated pigs (n = 50), ASFV-free field pigs (n = 100), and feral pigs (n = 6), confirmed 100% specificity. This robust assay provides a valuable tool for rapid and accurate ASF surveillance and control efforts, facilitating the timely detection and mitigation of outbreaks caused by emerging ASFV variants.

African swine fever (ASF), a highly contagious and lethal viral disease, continues to devastate the global swine industry. The emergence of ASF virus (ASFV) variants with varying genomic deletions poses significant challenges to ASF control. This study presents a novel, sensitive, and reliable quadplex real-time PCR assay for detecting ASFV variants lacking key genes (I177L, EP402R, and MGF360-14L), either individually or in combination. The assay targets conserved regions within these genes, ensuring broad coverage of diverse ASFV genotypes. A porcine beta-actin (ACTB) internal control was incorporated to minimize false-negative results. Optimization and evaluation using spike-in tests demonstrated high sensitivity with a limit of detection (LOD) ranging from 1-10 plasmid copies or 0.1 TCID₅₀ of ASFV isolates per reaction. No cross-reactivity was observed when testing serum samples from pigs infected with other common swine viruses. Further validation across a diverse panel of samples, comprising those from naturally ASFV-infected field pigs (n=54), experimentally ASFV-infected pigs (n=50), PBS-inoculated pigs (n=50), ASFV-free field pigs (n=100), and feral pigs (n=6), confirmed 100% specificity. This robust assay provides a valuable tool for rapid and accurate ASF surveillance and control efforts, facilitating the timely detection and mitigation of outbreaks caused by emerging ASFV variants.

African swine fever (ASF) is a highly contagious and severe hemorrhagic transboundary swine viral disease with up to a 100% mortality rate, which leads to a tremendous socio-economic loss worldwide. The lack of safe and efficacious ASF vaccines is the greatest challenge in the prevention and control of ASF. In this study, we generated a safe and effective live-attenuated virus (LAV) vaccine candidate VNUA-ASFV-LAVL3 by serially passaging a virulent genotype II strain (VNUA-ASFV-L2) in an immortalized porcine alveolar macrophage cell line (3D4/21, 50 passages). VNUA-ASFV-LAVL3 lost its hemadsorption ability but maintained comparable growth kinetics in 3D4/21 cells to that of the parental strain. Notably, it exhibited significant attenuation of virulence in pigs across different doses (10³, 10⁴, and 10⁵ TCID₅₀). All vaccinated pigs remained healthy with no clinical signs of African swine fever virus (ASFV) infection throughout the 28-day observation period of immunization. VNUA-ASFV-LAVL3 was efficiently cleared from the blood at 14–17 days post-infection, even at the highest dose (10⁵ TCID₅₀). Importantly, the attenuation observed in vivo did not compromise the ability of VNUA-ASFV-LAVL3 to induce protective immunity. Vaccination with VNUA-ASFV-LAVL3 elicited robust humoral and cellular immune responses in pigs, achieving 100% protection against a lethal wild-type ASFV (genotype II) challenge at all tested doses (10³, 10⁴, and 10⁵ TCID₅₀). Furthermore, a single vaccination (10⁴ TCID₅₀) provided protection for up to 2 months. These findings suggest that VNUA-ASFV-LAVL3 can be utilized as a promising safe and efficacious LAV candidate against the contemporary pandemic genotype II ASFV.

The 2023 International African Swine Fever Workshop (IASFW) took place in Beijing, China, on 18–20 September 2023. It was jointly organized by the U.S.-China Center for Animal Health (USCCAH) at Kansas State University (KSU) and the Chinese Veterinary Drug Association (CVDA) and sponsored by the United States Department of Agriculture Foreign Agricultural Service (USDA-FAS), Harbin Veterinary Research Institute, and Zoetis Inc. The objective of this workshop was to provide a platform for ASF researchers around the world to unite and share their knowledge and expertise on ASF control and prevention. A total of 24 outstanding ASF research scientists and experts from 10 countries attended this meeting. The workshop included presentations on current ASF research, opportunities for scientific collaboration, and discussions of lessons and experiences learned from China/Asia, Africa, and Europe. This article summarizes the meeting highlights and presents some critical issues that need to be addressed for ASF control and prevention in the future.

African swine fever virus (ASFV) is circulating in many swine-producing countries, causing significant economic losses. It is observed that pigs experimentally vaccinated with a live-attenuated virus (LAV) but not a killed virus (KV) vaccine develop solid homologous protective immunity. The objective of this study was to comparatively analyze antibody profiles between pigs vaccinated with an LAV vaccine and those vaccinated with a KV vaccine to identify potential markers of vaccine-induced protection. Thirty ASFV seronegative pigs were divided into three groups: Group 1 received a single dose of an experimental LAV, Group 2 received two doses of an experimental KV vaccine, and Group 3 was kept as a non-vaccinated (NV) control. At 42 days post-vaccination, all pigs were challenged with the parental virulent ASFV strain and monitored for 21 days. All pigs vaccinated with the LAV vaccine survived the challenge. In contrast, eight pigs from the KV group and seven pigs from the NV group died within 14 days post-challenge. Serum samples collected on 41 days post-vaccination were analyzed for their reactivity against a panel of 29 viral structural proteins. The sera of pigs from the LAV group exhibited a strong antibody reactivity against various viral structural proteins, while the sera of pigs in the KV group only displayed weak antibody reactivity against the inner envelope (p32, p54, p12). There was a negative correlation between the intensity of antibody reactivity against five ASFV antigens, namely p12, p14, p15, p32, and pD205R, and the viral DNA titers in the blood of animals after the challenge infection. Thus, antibody reactivities against these five antigens warrant further evaluation as potential indicators of vaccine-induced protection.

African swine fever (ASF) is a lethal and highly contagious transboundary animal disease with the potential for rapid international spread. Currently, there is no ASF vaccine commercially available. All infected animals must be isolated and culled immediately upon the confirmation of the presence of the virus. Studies leading to the rational development of protective ASF vaccines are urgently needed. Here, we generated a safe and efficacious live-attenuated vaccine (LAV) VNUA-ASFV-LAVL2 by serially passaging a field isolate (VNUA-ASFV-05L1, genotype II) in porcine alveolar macrophages (PAMs, 65 passages) and an immortalized porcine alveolar macrophage cell line (3D4/21, 55 passages). VNUA-ASFV-LAVL2 can efficiently replicate in both PAMs and 3D4/21 cells. It provides 100% protection, even with the low dose of 10² HAD₅₀, to the vaccinated pigs against the challenge of contemporary pandemic ASFV field isolate. Pigs vaccinated with this LAV in a dose range of 10² to 10⁵ HAD₅₀ remained clinically healthy during both the 28-day observation period of immunization and the 28-day observation period of challenge. VNUA-ASFV-LAVL2 was eliminated from blood by 28 days post-inoculation (DPI), and from feces or oral fluids by 17 DPI. Although the vaccine strain in serum remained a safe and attenuated phenotype after five passages in swine, a reversion-to-virulence study using blood or tissue homogenates at peak viremia will be conducted in the future. ASFV-specific IgG antibodies and significant cellular immunity were detected in vaccinated pigs before the ASFV challenge. These results indicate that the VNUA-ASFV-LAVL2 strain is a safe and efficacious LAV against the genotype II ASFV strain responsible for current ASF outbreaks in Asia.

African swine fever (ASF) is a lethal and highly contagious transboundary animal disease with the potential for rapid international spread. Currently, there is no ASF vaccine commercially available. All infected animals must be isolated and culled immediately upon confirmation of the presence of the virus. Works leading to the rational development of protective ASF vaccines are urgently needed. Here, we generated a safe and efficacious live-attenuated vaccine (LAV) VNUA-ASFV-LAVL2 by serial passaging of a field isolate (VNUA-ASFV-05L1, genotype II) in porcine alveolar macrophage (PAMs, 65 passages) and an immortalized porcine alveolar macrophage cell line (3D4/21, 55 passages). VNUA-ASFV-LAVL2 can efficiently replicate in both PAMs and 3D4/21 cells. It provides 100% protection, even with the low dose of 10^2 HAD50, for the vaccinated pigs against the challenge of contemporary pandemic ASFV field isolate. Pigs vaccinated with this LAV at a dose range of 10^2 to 10^5 HAD50 remained clinically healthy during both the 28-day observation period of immunization and the 28-day observation period of challenge. VNUA-ASFV-LAVL2 was completely eliminated from blood by 28 days post inoculation (DPI), and from feces or oral fluids by 17 DPI. It remained a safe, stable, and attenuated phenotype after five passages in pigs. Consistently high levels of ASFV-specific IgG antibodies and significant cellular immunity were detected in vaccinated pigs before the ASFV challenge. These results indicate that the VNUA-ASFV-LAVL2 strain is a safe and efficacious LAV against the genotype II ASFV strain responsible for current ASF outbreaks in Asia.