Explore the vast range of titles available.

Culicoides biting midges, small hematophagous dipterans, are the demonstrated or putative vectors of multiple arboviruses of veterinary and public health importance. Despite its relevance in disease spread, the ceratopogonid genus Culicoides is still a largely neglected group of species, predominantly because the major human-affecting arboviruses are considered to be transmitted by mosquitoes. However, when a pathogen is detected in a certain vector species, a thorough search for further vectors often remains undone and, therefore, the relevant vector species may remain unknown. Furthermore, for many hematophagous arthropods, true vector competence is often merely suspected and not experimentally proven. Therefore, we aim to illuminate the general impact of Culicoides biting midges and to summarize the knowledge about biting midge-borne disease agents using the order Bunyavirales, the largest and most diverse group of RNA viruses, as an example. When considering only viruses evidentially transmitted by Culicoides midges, the Simbu serogroup (genus Orthobunyavirus) is presumably the most important group within the virus order. Its members are of great veterinary importance, as a variety of simbuviruses, e.g., the species Akabane orthobunyavirus or Schmallenberg orthobunyavirus, induces severe congenital infections in pregnant animals. The major zoonotic representative of this serogroup occurs in South and Central America and causes the so-called Oropouche fever, an acute febrile illness in humans.

The ongoing SARS-CoV-2 pandemic necessitates the fast development of vaccines. Recently, viral mutants termed variants of concern (VOC) which may escape host immunity have emerged. The efficacy of spike encoding mRNA vaccines (CVnCoV and CV2CoV) against the ancestral strain and the VOC B.1.351 was tested in a K18-hACE2 transgenic mouse model. Naive mice and mice immunized with a formalin-inactivated SARS-CoV-2 preparation were used as controls. mRNA-immunized mice develop elevated SARS-CoV-2 RBD-specific antibody and neutralization titers which are readily detectable, but significantly reduced against VOC B.1.351. The mRNA vaccines fully protect from disease and mortality caused by either viral strain. SARS-CoV-2 remains undetected in swabs, lung, or brain in these groups. Despite lower neutralizing antibody titers compared to the ancestral strain BavPat1, CVnCoV and CV2CoV show complete disease protection against the novel VOC B.1.351 in our studies. Emerging SARS-CoV-2 variants with mutations in the spike protein raise concerns regarding vaccine efficacy. Here, the authors show that two spike encoding mRNA vaccines in preclinical and clinical development protect human ACE2 mice from the B.1.351 variant of concern and ancestral B BavPat1.

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.

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

Background Schmallenberg virus (SBV) was first detected in Germany in 2011 and today has an enzootic status in Central Europe. It is transmitted by biting midges of the genus Culicoides , which have a high abundance in livestock farms. In addition to SBV, Culicoides are considered vectors of other viruses relevant to livestock such as bluetongue virus (BTV) and epizootic haemorrhagic disease virus (EHDV). Monitoring of midges and transmitted viruses is of veterinary importance because the resulting diseases may cause animal suffering and entail economic losses due to control measures such as vaccination or trade restrictions. Methods To gain an overview of the prevalence of viruses in Culicoides vectors in Germany, a monitoring programme was established in 2018. From 2019 to 2023, biting midges were caught at 79 sites throughout the country, of which 511,788 were morphologically differentiated according to Culicoides species or subgenus and pooled accordingly. The nucleic acids extracted from 19,521 midge pools of up to 50 individuals were tested in real-time reverse transcription polymerase chain reactions (RT-PCRs) for the genomes of SBV, EHDV and BTV. The species in virus-positive pools were analysed with molecular biological methods to identify potential vector species. Results Whereas no EHDV and BTV were detected, SBV was found in every year of the five monitored years. The minimum infection rate (MIR) of SBV in the tested pools ranged from 3.75 in 2022 to 135.47 in 2023. Most SBV RNA-positive pools were represented by the subgenus Avaritia ( C. obsoletus , C. scoticus , C. dewulfi and C. chiopterus ). To a lesser extent, SBV RNA was detected in pools of the subgenus Culicoides ( C. punctatus , C. pulicaris , C. lupicaris and C. selandicus ). Only one pool of another subgenus, namely C. griseidorsum , was found positive for SBV genome. Conclusions The results from the monitoring programme confirm an enzootic circulation of SBV in the German Culicoides population during summer and autumn with varying infection rates between the years. The lack of detection of BTV in the midges may suggest a circulation of BTV at a low level. The absence of EHDV genome in biting midges is in line with the epidemiological situation in ruminants in Germany. Graphical Abstract

The Simbu serogroup of orthobunyaviruses includes several pathogens of veterinary importance, among them Schmallenberg virus (SBV), Akabane virus (AKAV) and Shuni virus (SHUV). They infect predominantly ruminants and induce severe congenital malformation. In adult animals, the intra vitam diagnostics by direct virus detection is limited to only a few days due to a short-lived viremia. For surveillance purposes the testing for specific antibodies is a superior approach. However, the serological differentiation is hampered by a considerable extent of cross-reactivity, as viruses were assigned into this serogroup based on antigenic relatedness. Here, we established a glycoprotein Gc-based triplex enzyme-linked immunosorbent assay (ELISA) for the detection and differentiation of antibodies against SBV, AKAV, and SHUV. A total of 477 negative samples of various ruminant species, 238 samples positive for SBV-antibodies, 36 positive for AKAV-antibodies and 53 SHUV antibody-positive samples were tested in comparison to neutralization tests. For the newly developed ELISA, overall diagnostic specificities of 84.56%, 94.68% and 89.39% and sensitivities of 89.08%, 69.44% and 84.91% were calculated for SBV, AKAV and SHUV, respectively, with only slight effects of serological cross-reactivity on the diagnostic specificity. Thus, this test system could be used for serological screening in suspected populations or as additional tool during outbreak investigations.

BTV-3 emerged in the Netherlands in 2023 and spread rapidly to neighboring countries. Compared to the BTV-8 outbreak in 2006, the course of the BTV-3 epizootic is more severe. Experimental infection of laboratory-reared Culicoides sonorensis midges showed a slightly higher replication rate of BTV-3 than of BTV-8. We experimentally infected laboratory-reared Culicoides sonorensis biting midges with bluetongue virus (BTV) serotypes 3 and 8 using virus-containing blood meal and found slightly higher replication rates of BTV-3.

The teratogenic orthobunyavirus Schmallenberg virus (SBV) is transmitted between its mammalian hosts by Culicoides biting midges. The genome of circulating SBV, i.e. variants present in viraemic ruminants or insect vectors, is very stable, while variants found in malformed ruminant foetuses display a high genetic variability. It was suggested that foetal infection provides an environment that favours viral mutations that enable immune escape in the unborn, but at the costs of limiting the ability of the virus to spread further. To investigate infection and dissemination rates of different SBV variants in the insect vectors, we fed laboratory-reared Culicoides sonorensis with blood containing the prototype strain BH80/11-4 from a viraemic cow or strain D281/12, which was isolated from the brain of a sheep foetus and harbours multiple mutations in all three genome segments. Further, virus variants lacking NSs, NSm or both non-structural proteins were included. Six days after feeding, virus replication was found in about 2% of the midges exposed to wild-type strain BH80/11 4. The absence of the non-structural proteins had no obvious effect on the oral susceptibility to virus infection, as 2.78% of the midges fed with the NSs-deletion mutant displayed after six days viral loads higher than the respective day-0-group, 1.92% of the midges exposed to the NSm-deletion mutant and 1.55% of midges exposed to the NSs/NSm-deletion mutant. In contrast, strain D281/12 did not replicate at all in the midges, supporting the assumption that SBV variants arising in infected foetuses are unable to enter the normal insect-mammalian host cycle.Competing Interest StatementThe authors have declared no competing interest.