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In July 2024, bluetongue virus serotype 3 (BTV-3) was first detected in southern Belgium, marking the onset of a major epidemic wave. This study documents, for the first time in Belgium, the ability of BTV-3 to cross the placental barrier in cattle, causing abortions and congenital central nervous system malformations. Abortion cases from January to December 2024 were monitored through the national abortion protocol, which mandates reporting and laboratory investigation (i.e., the year of emergence and the three previous years as the baseline data set). Among 5,751 reported abortions, 903 foetuses were tested by PCR, revealing widespread BTV-3 circulation. The first malformed PCR-positive foetus was recorded in mid-August, four weeks after a sharp increase in abortion rates. Lesions such as hydranencephaly were confirmed in PCR-positive foetuses, with a malformation rate of 32.24% in affected herds from weeks 36 to 52 (i.e., 22 times higher than in previous years). Gestational stage analysis indicated that congenital lesions were most frequent following infection between 70 and 130 days of gestation. Based on the observed gross lesions and the timing of abortion, it was deduced that the earliest maternal infections likely occurred in February–March 2024, implying low-level winter BTV-3 circulation before the official detection of the epidemic wave. These findings highlight the epidemiological value of systematic abortion monitoring as an early warning system tool and highlight the inadequacy of relying solely on clinical surveillance in adult ruminants. The abrupt emergence of BTV-3 across the territory without a gradual spatial spread underscores the need for anticipatory control strategies. Strategic, multivalent vaccination campaigns and enhanced abortion surveillance are critical to mitigate similar reproductive and economic losses in future bluetongue outbreaks.

To monitor the epidemiological situation of bluetongue virus (BTV) in Belgium, a national surveillance programme was conducted during the 2024–2025 winter season. The objective was to estimate the apparent seroprevalence of BTV-3 following the 2023–2024 epidemic and to prove the absence of active circulation of other BTV serotypes in mixed herds (cattle and sheep). A total of 2551 cattle and 1458 sheep were sampled across Belgium. Serological analyses were performed using ELISA, and molecular detection of BTV-3, BTV-8, and BTV-12 was conducted by RT-qPCR. The majority of cattle and sheep herds showed evidence of exposure to BTV-3, with a very high herd-level apparent seroprevalence (100%; 95% CI: 96.2–100% in cattle and 98.9%; 95% CI: 93.8–99.8% in sheep). Apparent within-herd seroprevalence was also high in cattle (94.6%; 95% CI: 91.8–96.5%) and sheep (85.5%; 95% CI: 80.4–89.5%). No evidence of active circulation of BTV-8 or BTV-12 was detected. A moderate significant positive correlation between Ct values and sampling date was observed both for bovine and ovine samples, consistent with a progressive decline in detectable BTV RNA during winter in the absence of vector activity.

Between 2006 and 2010, northwestern Europe experienced its first significant bluetongue virus (BTV) outbreak, driven by the spread of BTV-8, which had major repercussions on the European livestock sector. While BTV-3 was first identified in Europe in Italy in 2017, a new introduction of the virus was reported in 2023, in the Netherlands, and subsequently spread rapidly across the continent. A limited number of BTV-3 outbreaks were notified in Belgium in 2023, leading to the loss of its BTV-free status. In the following year, 2024, the virus spread throughout the country in a short time period. This study describes the impact of BTV-3 circulation in Belgium in 2024, detailing both its geographic spread and the associated increase in mortality, reduced births recorded, and decline in milk production among ruminants. Furthermore, preliminary results on the effectiveness of field vaccination and maternal immunity transfer are presented, as well as critical gaps that hinder the development of a robust, evidence-based management strategy. As the epidemiological situation is expected to become more complex in the future, due to the co-circulation of multiple BTV serotypes and other Culicoides-borne diseases, such as EHDV, effective collaboration and communication among stakeholders and international authorities will be crucial for implementing measures to mitigate the spread of these diseases.

From 2017 to 2019, several vaccine-like recombinant strains of lumpy skin disease virus (LSDV) were discovered in Kazakhstan and neighbouring regions of Russia and China. Shortly before their emergence, the authorities in Kazakhstan launched a mass vaccination campaign with the Neethling-based Lumpivax vaccine. Since none of the other countries in the affected region had used a homologous LSDV vaccine, it was soon suspected that the Lumpivax vaccine was the cause of these unusual LSDV strains. In this study, we performed a genome-wide molecular analysis to investigate the composition of two Lumpivax vaccine batches and to establish a possible link between the vaccine and the recent outbreaks. Although labelled as a pure Neethling-based LSDV vaccine, the Lumpivax vaccine appears to be a complex mixture of multiple CaPVs. Using an iterative enrichment/assembly strategy, we obtained the complete genomes of a Neethling-like LSDV vaccine strain, a KSGP-like LSDV vaccine strain and a Sudan-like GTPV strain. The same analysis also revealed the presence of several recombinant LSDV strains that were (almost) identical to the recently described vaccine-like LSDV strains. Based on their InDel/SNP signatures, the vaccine-like recombinant strains can be divided into four groups. Each group has a distinct breakpoint pattern resulting from multiple recombination events, with the number of genetic exchanges ranging from 126 to 146. The enormous divergence of the recombinant strains suggests that they arose during seed production. The recent emergence of vaccine-like LSDV strains in large parts of Asia is, therefore, most likely the result of a spillover from animals vaccinated with the Lumpivax vaccine.

The current epidemic in Asia, driven by LSDV recombinants, poses difficulties to existing DIVA PCR tests, as these do not differentiate between homologous vaccine strains and the recombinant strains. We, therefore, developed and validated a new duplex real-time PCR capable of differentiating Neethling-based vaccine strains from classical and recombinant wild-type strains that are currently circulating in Asia. The DIVA potential of this new assay, seen in the in silico evaluation, was confirmed on samples from LSDV infected and vaccinated animals and on isolates of LSDV recombinants (n = 12), vaccine (n = 5), and classic wild-type strains (n = 6). No cross-reactivity or a-specificity with other capripox viruses was observed under field conditions in non-capripox viral stocks and negative animals. The high analytical sensitivity is translated into a high diagnostic specificity as more than 70 samples were all correctly detected with Ct values very similar to those of a published first-line pan capripox real-time PCR. Finally, the low inter- and intra-run variability observed shows that the new DIVA PCR is very robust which facilitates its implementation in the lab. All validation parameters that are mentioned above indicate the potential of the newly developed test as a promising diagnostic tool which could help to control the current LSDV epidemic in Asia.

Epizootic haemorrhagic disease virus serotype 8 (EHDV-8) is an emerging Culicoides -borne virus that was first detected in Europe in autumn 2022 in Italy and subsequently spread to Spain, Portugal and France. Despite its economic impact, little is known about its tissue distribution, persistence, and induction of immune responses in cattle. Therefore, we conducted an experimental infection study in groups of 3 cattle inoculated intradermally (ID; 10 6.2 or 10 5.2 TCID 50 /animal) or subcutaneously (SC, 10 6.2 TCID 50 /animal) with a Spanish EHDV-8 isolate. Viremia appeared at 3 days post-inoculation (dpi), peaked at 7–10 dpi, and persisted until the end of the study (21 dpi). Fever spiked at 8–9 dpi with a longer duration in the high-dose groups. No other clinical symptoms were noted, except in one animal from the SC high-dose group. This animal exhibited apathy, conjunctivitis, and swollen lymph nodes from 10 dpi onwards. At necropsy, lymph nodes and spleen contained higher viral loads than muscles, brain, and skin. The clinical animal displayed petechiae on the kidney with high viral loads (Ct value = 20), which was an outlier compared with all other organs tested. The virological data thus confirmed that blood, spleen and lymph nodes are the most suitable diagnostic samples. A strong humoral response (100% seroconversion) was observed in all the groups at 10 dpi. All the animals, except the one showing clinical signs, also exhibited a strong cellular immune response, with IFN-γ levels peaking at 5–7 dpi. In conclusion, this study demonstrated that the inoculation route and dose only minimally impacted viremia, viral spread and induced immune responses.

Homologous vaccination has proven to be an effective tool to control and eradicate lumpy skin disease. However, their use has been met with some trepidation for diverse reasons, in some regions, and has resulted in the use of heterologous vaccines (sheeppox or goatpox-based). However, conflicting data (field and experimental) raises questions about their effectiveness. As comparative data under standardized conditions are lacking, this study aimed to evaluate four sheeppox-based and one goatpox-based vaccine using a standard vaccination/challenge protocol previously used to evaluate homologous LSDV vaccines. Although some minor differences were observed between the different sheeppox-based vaccines, none of them were able to completely protect the animals against a virulent LSDV challenge, as witnessed by the development of nodules, viremia and the detection of viral genomes in the different organs and tissues. In contrast, the goatpox-based vaccine provided complete protection (no nodules nor viremia) and induced an immunological profile (seroconversion and IFNγ response) similar to the homologous vaccines. Based upon the obtained data it can be concluded that none of the tested sheeppox-based vaccines are suitable for vaccination to prevent LSDV infection, at the dose used, while the goatpox-based vaccine, Caprivac, is. It should, however, be emphasized that this cannot be extrapolated to other goatpox-based vaccines without extensive validation.

Lumpy skin disease virus (LSDV) is a vector-transmitted capripox virus that causes disease in cattle. Stomoxys calcitrans flies are considered to be important vectors as they are able to transmit viruses from cattle with the typical LSDV skin nodules to naive cattle. No conclusive data are, however, available concerning the role of subclinically or preclinically infected cattle in virus transmission. Therefore, an in vivo transmission study with 13 donors, experimentally inoculated with LSDV, and 13 naïve acceptor bulls was performed whereby S. calcitrans flies were fed on either subclinical- or preclinical-infected donor animals. Transmission of LSDV from subclinical donors showing proof of productive virus replication but without formation of skin nodules was demonstrated in two out of five acceptor animals, while no transmission was seen from preclinical donors that developed nodules after Stomoxys calcitrans flies had fed. Interestingly, one of the acceptor animals which became infected developed a subclinical form of the disease. Our results show that subclinical animals can contribute to virus transmission. Therefore, stamping out only clinically diseased LSDV-infected cattle could be insufficient to completely halt the spread and control of the disease.

Vaccines form the cornerstone of any control, eradication and preventative strategy and this is no different for lumpy skin disease. However, the usefulness of a vaccine is determined by a multiplicity of factors which include stability, efficiency, safety and ease of use, to name a few. Although the vaccination campaign in the Balkans against lumpy skin disease virus (LSDV) was successful and has been implemented with success in the past in other countries, data of vaccine failure have also been reported. It was therefore the purpose of this study to compare five homologous live attenuated LSDV vaccines (LSDV LAV) in a standardized setting. All five LSDV LAVs studied were able to protect against a challenge with virulent LSDV. Aside from small differences in serological responses, important differences were seen in side effects such as a local reaction and a Neethling response upon vaccination between the analyzed vaccines. These observations can have important implications in the applicability in the field for some of these LSDV LAVs.

Vaccination is an effective approach to prevent, control and eradicate diseases, including lumpy skin disease (LSD). One of the measures to address farmer hesitation to vaccinate is guaranteeing the quality of vaccine batches. The purpose of this study was to demonstrate the importance of a quality procedure via the evaluation of the LSD vaccine, Lumpivax (Kevevapi). The initial PCR screening revealed the presence of wild type LSD virus (LSDV) and goatpox virus (GTPV), in addition to vaccine LSDV. New phylogenetic PCRs were developed to characterize in detail the genomic content and a vaccination/challenge trial was conducted to evaluate the impact on efficacy and diagnostics. The characterization confirmed the presence of LSDV wild-, vaccine- and GTPV-like sequences in the vaccine vial and also in samples taken from the vaccinated animals. The analysis was also suggestive for the presence of GTPV-LSDV (vaccine/wild) recombinants. In addition, the LSDV status of some of the animal samples was greatly influenced by the differentiating real-PCR used and could result in misinterpretation. Although the vaccine was clinically protective, the viral genomic content of the vaccine (being it multiple Capripox viruses and/or recombinants) and the impact on the diagnostics casts serious doubts of its use in the field.