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In October 2023, bluetongue virus serotype 3 (BTV-3) emerged in Germany, where Schmallenberg virus is enzootic. We detected BTV-3 in 1 pool of Culicoides biting midges collected at the time ruminant infections were reported. Schmallenberg virus was found in many vector pools. Vector trapping and analysis could elucidate viral spread.

A devastating bluetongue (BT) epidemic caused by bluetongue virus serotype 3 (BTV-3) has spread throughout most of the Netherlands within two months since the first infection was officially confirmed in the beginning of September 2023. The epidemic comes with unusually strong suffering of infected cattle through severe lameness, often resulting in mortality or euthanisation for welfare reasons. In total, tens of thousands of sheep have died or had to be euthanised. By October 2023, more than 2200 locations with ruminant livestock were officially identified to be infected with BTV-3, and additionally, ruminants from 1300 locations were showing BTV-associated clinical symptoms (but not laboratory-confirmed BT). Here, we report on the spatial spread and dynamics of this BT epidemic. More specifically, we characterized the distance-dependent intensity of the between-holding transmission by estimating the spatial transmission kernel and by comparing it to transmission kernels estimated earlier for BTV-8 transmission in Northwestern Europe in 2006 and 2007. The 2023 BTV-3 kernel parameters are in line with those of the transmission kernel estimated previously for the between-holding spread of BTV-8 in Europe in 2007. The 2023 BTV-3 transmission kernel has a long-distance spatial range (across tens of kilometres), evidencing that in addition to short-distance dispersal of infected midges, other transmission routes such as livestock transports probably played an important role.

In September 2024, bluetongue virus serotype 3 (BTV-3) was first identified in Portugal, specifically in the Alentejo region (Évora District), using molecular diagnostic methods. The initial case involved a sheep exhibiting severe clinical symptoms, including head oedema, prostration, nasal discharge, and significant respiratory distress. A subsequent case was documented in another sheep from a different farm within the same district, which presented with high fever (41.5 °C), nasal discharge, and arthritis, ultimately resulting in mortality. Within one month of these initial detections, additional cases in both sheep and cattle were reported in neighbouring districts, indicating the virus rapid spread within the region. In response to this emerging threat, extensive monitoring efforts are being undertaken to delineate the distribution of BTV-3, and vaccination campaigns targeting this serotype have been initiated. These measures aim to mitigate the impact of the virus on livestock health and prevent further transmission.

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.

The first official case of bluetongue virus serotype 3 (BTV-3) in Portugal was confirmed in sheep from the district of Évora in September 2024. Notably, mortality was observed in pregnant sheepdogs within the affected sheep flocks. This study presents four cases of pregnant dogs infected with BTV-3 in mid-September 2024, all of which aborted prior to death. BTV-3 was identified by RT-qPCR following initial positive results from pan-BTV RT-qPCR. The virus was subsequently isolated from the blood of one of the dogs in BHK-21 cells, and a partial sequence of the vp2 gene was obtained. This sequence showed 100% similarity to sheep BTV3/3234/PT2024, identified in Portugal in September 2024, as well as to BTV-3/NET2023, first reported in the Netherlands in 2023. These findings suggest that the viruses may be related or share a common origin. Co-infection with common canine viruses and pathogenic bacteria was ruled out, confirming that the fatalities were due to BTV-3 infection, probably by ingestion of sheep placenta after lambing. Our results confirm the potential for the transmission of BTV-3 to non-ruminant species, particularly carnivores, and, therefore, the wider ecological implications of this virus. In addition, the identification of transplacental transmission of BTV-3 in one of the dogs provides new evidence highlighting the complexity of the virus’ transmission mechanisms.

Background Bluetongue virus (BTV) is the etiologic agent of a major infectious disease of livestock and is transmitted between its ruminant hosts by Culicoides biting midges. The first outbreak ever recorded in central Europe was caused by serotype BTV-8 and led to a major epidemic. In 2023, serotype BTV-3 emerged in the Netherlands and spread rapidly to neighbouring countries. Compared with the BTV-8 outbreak in 2006, the course of the BTV-3 epizootic is more severe, in regards to clinical signs and faster spread of the virus. Methods To explore possible causes of the different epidemiologies, we performed laboratory infection experiments and compared the replication properties of BTV-8 and BTV-3 in Culicoides sonorensis biting midges. Results Oral infection with BTV-3 resulted in a significantly higher viral load in the infected midges with demonstrated replication than BTV-8 infection. Conclusions The higher viral load observed in midges with BTV-3 replication than in midges with BTV-8 replication may be a factor contributing to the observed faster outbreak progression of the current BTV-3 outbreak in comparison to the BTV-8 outbreak in 2006/2007. Graphical Abstract

Bluetongue virus serotype 3 (BTV-3) emerged in northwestern Europe in 2023–2024, raising concerns about its potential reproductive impact on rams, similar to previous outbreaks with BTV-8. This study assessed the effect of natural BTV-3 infection on the semen quality of 49 rams in Belgium using two cross-sectional sampling sessions during the 2024 outbreak. Semen and blood were tested for BTV RNA via RT-qPCR, and a composite semen quality score (SQS) was established based on key sperm parameters. On the first sampling date, 75% of rams were viremic, and 19% presented azoospermia. Rams with BTV RNA detectable in both semen and blood had significantly lower SQS and sperm concentrations than those with viral RNA in blood only or none at all. By the second sampling, 53 days later, semen quality had improved markedly, indicating a transient effect of infection. These findings confirm that BTV-3 can severely but temporarily impair ram fertility, particularly when viral replication occurs in the reproductive tract. Given the seasonal overlap between vector activity and breeding programs, these results underscore the importance of integrating reproductive health monitoring into outbreak response strategies.

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.

Since the emergence of serotype BTV-3, another bluetongue virus, in fall 2023, this variant has been causing great losses in livestock farming in Europe. The virus spreads faster than the epidemic BTV-8, which appeared on the continent nine years earlier. This study describes the first case of BTV-3 in Poland detected in a European bison (Bison bonasus) in Poland’s Wolin National Park, approximately 15 km from the German–Polish border. The animal suffered from a severe and fatal hemorrhagic disease. The symptoms included respiratory problems, bloody diarrhea, and rapidly progressive cachexia. In addition to the virus’s confirmation as BTV-3 and the presence of the infecting agent in the blood and spleen of the animal, the virus was also detected in one pool of blood-fed Culicoides punctatus caught near the bison enclosure two weeks after the death of the bison. This is the first detection of BTV-3 in C. punctatus, which suggests vector competency for this serotype. Phylogenetic analysis based on segment 2 of the virus revealed the homology of the Polish isolate to the BTV-3 strains circulating in the Netherlands, Germany, and Portugal, and slightly lower similarity to the BTV-3 strains detected in sheep in Sardinia (Italy) in 2018 and in Tunisia in November 2016. A retrospective serosurvey of the exposure to BTV in thirteen other European bison populations distributed over the country indicated that the observed case at the Wolin National Park was the first BTV-3 to be detected in Poland.

The epidemiological patterns of Bluetongue (BT) in North Africa and Mediterranean Basin (MB) dramatically changed by emergence of subsequent episodes of novel bluetongue virus (BTV) serotypes with highly pathogenic indexes and socio‐economic impacts. The objective of the study was to investigate the sero‐prevalence and serotype distribution of BTV in Libya. During 2015‐2016, a total of 826 serum samples were collected from domestic ruminants in Libya. All sera were assayed by competitive enzyme‐linked immunosorbent assays (c‐ELISA). C‐Elisa‐positive samples (43.3%; 173/400) were further analyzed by virus neutralization assay to identify BTV serotypes and determine the antibody titre of positive samples. An overall BTV sero‐prevalence was 48.4% (95% CI: 45.0%‐51.8%). Neutralizing antibodies were detected against the following BTV serotypes namely: BTV‐1, BTV‐2, BTV‐3, BTV‐4, BTV‐9 and BTV‐26. While BTV‐1, BTV‐2, BTV‐4 and BTV‐9 circulation was unsurprising as they have been responsible of the last year outbreaks in Northern African Countries, the detection of BTV‐3 and BTV‐26 was definitely new and concerning for the animal health of the countries facing the Mediterranean Basin. It is crucial that European and Northern African authorities collaborate in organizing common surveillance programmes to early detect novel strains or emerging serotypes in order to set up proper preventive measures, and, in case, develop specific vaccines and plan coordinated vaccination campaigns. This study is the first investigation on the sero‐prevalence and serotype distribution of BTV in Libya. In line with other Northern African countries, the obtained results (48.4%; 95% CI: 45.0–51.8%) in sheep, goats and cattle confirmed that, at least in the surveyed regions and provinces, BT is endemic in Libya. The results of this study are original and interesting offering precious and valuable information for the European and northern African Scientific communities.