African swine fever is a hemorrhagic viral disease with a mortality rate of nearly 100% in pigs. Hence, it is classified as a notifiable disease by the World Organization for Animal Health. Because no field-available vaccine exists, African swine fever virus (ASFV) control and eradication solely depend on good farm biosecurity management and rapid and accurate diagnosis. In this study, we developed a new indirect serological enzyme-linked immunosorbent assay (ELISA) using recombinant p11.5 protein from ASFV as a solid-phase target antigen. The cutoffs were determined by receiver operating curve analysis performed with serum samples obtained from naïve and infected pigs. Based on the results of a commercially available serological ELISA, the relative sensitivity and specificity of our assay were 93.4% and 94.4% (N = 166; area under the curve = 0.991; 95% confidence interval = 0.982–0.999), respectively. Furthermore, to compare the performance of the serological ELISAs, we conducted the assays on a panel of sera collected from pigs and boars experimentally infected with different ASFV isolates. The results indicated the greater sensitivity of the newly developed assay and its ability to detect anti-ASFV antibodies earlier after virus inoculation.

ランピースキン病（Lumpy Skin Disease, LSD）は，ランピースキン病ウイルス（LSD virus, LSDV）によって引き起こされる牛および水牛のウイルス感染症である．LSDを発症した動物では，全身，時には局所の皮膚に多数の結節が形成されるとともに，発熱，乳量の低下，流産などの臨床症状が認められる．皮膚の結節病変や，壊死して脱落した組織（sit-fast）には極めて大量のウイルスが含まれること，また環境中でのウイルスの安定性が高いことから，これらは水平伝播の重要な感染源となる．ただし，LSDVの感染は，主にヌカカ，サシバエ，ダニなどの吸血性の節足動物（ベクター）の咬刺によるため，本病の農場への侵入防止にはこれらのベクター防除対策が重要になる．予防には弱毒生ワクチンが有効であり，広く使用されているが，多くの発生国では本病を制圧するまでには至っていない．アジアでは，2019年に中国でLSDが発生して以降，東南アジアおよび東アジア諸国で発生が継続しており，我が国でも2024年11月に国内初発例が福岡県で確認された．本年1月以降（６月20日現在まで），国内での新たな発生は報告されていないが，周辺国では依然として流行が継続していることから，再侵入のリスクは引き続き高いと言える．

Background: Highly potent vaccines are essential for the effective control of classical swine fever (CSF). Since CSF re-emerged in 2018 in Japan, the live CSF virus (CSFV) vaccine—a guinea pig exaltation of Newcastle disease virus-negative strain vaccine (GPE⁻, genotype 1.1)—has been applied to domestic pigs, contributing to a reduction in outbreaks. Meanwhile, the persistence and continued expansion of CSFV in wild boar populations have raised concerns regarding potential antigenic divergence. Methods: We systematically evaluated the neutralizing reactivity of sera from GPE⁻-vaccinated pigs against CSFV strains (genotype 2.1) recently circulating in Japan against identified a representative strain that showed markedly reduced neutralization. We directly assessed the protective efficacy of the GPE⁻ vaccine against this strain in a controlled challenge experiment. At 4 weeks post-vaccination, both vaccinated and unvaccinated pigs were orally challenged with the representative Japanese strain and monitored for 3 weeks thereafter. Results: Among the Japanese CSFV strains, the JPN/SM/WB/2022 isolate exhibited markedly reduced neutralizing reactivity—over 32-fold lower than that against the vaccine strain—when tested with GPE⁻ vaccine-induced antisera. In the experimental infection in pigs, unvaccinated pigs exhibited typical clinical signs of CSF and viremia, and two pigs reached the humane endpoint. In contrast, none of the vaccinated pigs showed any clinical signs of infection. Robust humoral and cellular immune responses were induced in vaccinated pigs, which may correlate with the observed complete protection. Conclusions: The GPE^– live vaccine provides protective immunity against an antigenically distinct strain, prevents disease, and limits viral spread in domestic pigs.

African swine fever (ASF) is a highly fatal, febrile infectious disease of domestic pigs and wild boars caused by the African swine fever virus (ASFV). Recently, highly virulent recombinant ASFVs with chimeric genomes derived from p72 genotype I and II viruses have emerged in China, Vietnam, and Russia. These genotype I/II recombinants can evade immunity induced by genotype II–based vaccines, thereby complicating disease control efforts. To address this challenge, a novel duplex quantitative PCR (qPCR) assay was developed to simultaneously detect and differentiate genotypes I, II, and I/II recombinants in a single reaction. The assay exhibited high sensitivity and specificity, with a reliable detection limit of 10 copies/reaction for genotype I and II ASFV DNA. Validation using clinical samples collected in northern Vietnam in 2025 confirmed a robust performance in accurately distinguishing circulating genotype II viruses from recombinant genotype I/II viruses, including the detection of potential co-infection. Whole-genome sequencing of selected positive samples further corroborated these findings. Overall, this qPCR assay provides a precise and efficient tool for identifying currently circulating ASFV genotypes, thereby facilitating improved disease surveillance and supporting a comprehensive understanding of the evolving epidemiological landscape of ASF in regions with increasing viral genetic diversity.