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We report Sindbis virus circulation in the Netherlands based on serologic evidence found in 6 resident wild birds and 3 horses (2021-2022). Tested mosquitoes were molecularly negative, and humans were serologically negative. Veterinarians and health practitioners in the Netherlands should be aware of the importance of surveillance for Sindbis virus.

Analyses of mosquito-borne virus outbreaks have revealed the presence of similar virus strains over several years. However, it remains unclear how mosquito-borne viruses can persist over winter, when conditions are generally unfavorable for virus circulation. One potential route for virus persistence is via diapausing mosquitoes. We therefore studied whether Usutu virus (USUV), West Nile virus (WNV) and/or Sindbis virus (SINV) can be identified in diapausing mosquitoes in The Netherlands. Mosquito collections were carried out in November 2022 in hibernacula located in two areas with previously observed WNV and/or USUV activity. A total of 4857 mosquitoes, belonging to four species (groups) ( Culex pipiens/torrentium , Culiseta annulata , Anopheles maculipennis s.l. and Culex territans ), were collected. WNV-, USUV- and SINV-screening using a multiplex real-time RT-PCR assay was carried out on mono-specific mosquito pools. One Culex pipiens / torrentium pool tested positive for USUV RNA. Whole genome sequencing and subsequent phylogenetic analysis revealed that the virus belongs to USUV lineage Africa 3 and clusters with other USUV sequences derived from The Netherlands in 2022. This finding confirms our hypothesis of the potential of local overwintering of USUV in diapausing mosquitoes in The Netherlands. Graphical Abstract

Arboviruses (i.e., Arthropod-borne viruses) pose a threat to human health worldwide. This taxonomically-diverse group includes numerous viruses that recurrently spread into new regions. Therefore, periodic surveys of the arboviral diversity in a given region can help optimize the diagnosis of arboviral infections. However, such surveys are infrequent, especially in low-income countries. Consequently, case investigation is often limited to a fraction of the arboviral diversity. This situation is likely to result in undiagnosed cases. Here, we investigated the diversity of mosquito-borne arboviruses in two regions of Burkina Faso. To this end, we used untargeted metagenomics to screen mosquitoes collected over three years in six urban and rural areas. The analysis focused on two mosquito species, Aedes aegypti and Culex quinquefasciatus , considered to be among the most important vectors of arboviruses worldwide. The screening detected Sindbis virus (SINV, Togaviridae ) for the first time in Burkina Faso. This zoonotic arbovirus has spread from Africa to Europe. SINV causes periodic outbreaks in Europe but its distribution and epidemiology in Africa remains largely unstudied. SINV was detected in one of the six areas, and at a single year. Detection was validated with isolation in cell culture. SINV was only detected in Cx. quinquefasciatus , adding to the list of potential vectors of SINV in nature. The SINV infection rate in mosquitoes was similar to those observed in European regions experiencing SINV outbreaks. Phylogenetic analysis placed the nearly-full genome within a cluster of Central African strains of lineage I. This cluster is thought to be at the origin of the SINV strains introduced into Europe. Our results call for studies on the prevalence of SINV infections in the region to estimate the disease burden and the interest of SINV diagnostic in case investigation.

Mosquitoes play a crucial role as vectors of disease pathogens and are among the most socioeconomically important animals in the world. Medically important arboviruses include the Sindbis virus (SINV), which causes chills, skin rashes, and joint pain. Endemic in northern Europe, SINV has been increasingly detected in central Europe. The main objectives of this study were to monitor and screen mosquitoes for the presence of SINV. We included samples of mosquitoes collected throughout the years at different locations in Slovenia. The mosquitoes were first identified and then pooled according to species, sex, date of sampling, and location. Nucleic acid (NA) was isolated from these pools, and the target segment of the SINV genome was amplified using molecular methods. We performed detailed phylogenetic analyses of the SINV‐positive mosquito pools. From 2020 to 2024, we monitored mosquitoes at 226 locations in Slovenia and collected 112,001 samples, which were identified and grouped into 11,595 pools. Using real‐time reverse transcription polymerase chain reaction (RT‐PCR), we found SINV RNA in five pools of Culex modestus mosquitoes collected in two regions of northeastern Slovenia in August 2022 and in July, August, and September 2024. The SINV discovered in Slovenia (SINV‐SLO) was classified as Genotype IV. We designed a primer scheme for the whole‐genome amplification of SINV based on the alignment of the available SINV‐IV sequences and performed molecular characterization of the sequences. Our findings revealed that SINV‐SLO is closely related to the SINV strains identified in Russia, Azerbaijan, and China. In Europe, it is Genotype I that is most frequently detected and causes epidemics, whereas Genotype IV, which was detected in Slovenia, has not yet been associated with disease outbreaks.

Sindbis virus (SINV) is a zoonotic arbovirus transmitted by mosquitoes and maintained by wild birds with an expanding distribution globally. Despite its importance, surveillance efforts are low or lacking in many areas, especially in Africa. Our study aimed to highlight the epidemiology of SINV in wild birds in a West African country – Nigeria – with implications for human health. Blood samples were collected from wild resident Afrotropical and migrant Palearctic birds over two years. RT-qPCR was used to detect SINV RNA positive samples, followed by confirmatory conventional PCR and Sanger sequencing targeting the non-structural protein gene. Three out of 504 samples (0.6%; 95% CI: 0.12–1.73%) were positive for SINV, all from individuals of a single species, the African Thrush ( Turdus pelios ). We successfully generated the whole genome sequence of one sample. Phylogenetic analysis revealed it was closely related to strains from Algeria, Spain and Kenya in the SINV-I genotype. The study suggests that SINV is enzootic in the region and that the African Thrush may be a putative reservoir species.

Background As living vectors, arthropods play a crucial role in the transmission of viruses, bacteria and parasites. Previous research on virus transmission has focussed mainly on the roles of mosquitoes and ticks, while the potential importance of other blood-sucking arthropods such as louse flies (Hippoboscidae) has been somewhat neglected. The aim of this study was to detect viruses in avian louse flies from Germany to assess whether they could be used as sentinel organisms for monitoring arboviruses with zoonotic potential. Methods We collected 1000 louse flies of the species Crataerina hirundinis, C. pallida, Ornithomya avicularia, O. biloba, O. fringillina, O. chloropus, Ornithophila metallica and Pseudolynchia canariensis in Germany and screened the samples via RT-PCR for West Nile virus (WNV), Usutu virus (USUV) and Sindbis virus (SINV), which are arboviruses with avian hosts as reservoirs. Results While WNV was not detected, we found one louse fly positive for USUV and one for SINV RNA, both of which belonged to the species O. avicularia ( n  = 279). Therefore, the detection rates for both USUV and SINV were 0.1% (95% CI 0.0–0.3%) in the total sample and 0.36% (95% CI 0.00–1.09%) in O. avicularia . For the sample that tested positive for SINV, the PCR results were confirmed by sequencing a 288-bp segment that encoded part of the virus’s structural polyprotein. Conclusions This is the first time that USUV RNA and SINV RNA have been detected in louse flies. In addition, it is the first detection of human pathogenic viruses in the louse fly species O. avicularia . The results of this study indicate that louse flies should not be neglected as possible sentinels of viral pathogens with zoonotic potential in the sense of the One Health concept. Graphical abstract

Outbreaks of zoonotic arboviruses originating in Africa occur amidst complex ecological changes and are increasingly emerging as important neglected tropical diseases. Despite sporadic epizootics and human cases of Wesselsbron virus (WSLV), Sindbis virus (SINV), and Middelburg virus (MIDV) in Africa, knowledge of associated risks remains insufficient for prevention. We developed species distribution models for the three viruses alongside five key vectors, Aedes circumluteolus and Aedes mcintoshi for WSLV; Culex univittatus and Culex pipiens for SINV; and Mansonia africana and Aedes mcintoshi for MIDV that indicate areas with ecological suitability for the arboviruses in Africa. We integrated virus and mosquito species occurrence data with climate and land-use data for current (2015) and future (2021 - 2040) scenarios under two shared socioeconomic pathways of emission and climate projections. We applied the Maxent algorithm and evaluated over 100 candidate models per species, selecting those with above-random predictive performance based on high mean Area Under the Curve ratios (Range = 1.45 - 1.88). Our models revealed high ecological suitability for the five mosquitoes in Equatorial and Southern Africa and predict emerging ecologically suitable hotspots for arboviral presence in Southern and Eastern regions, with potential future expansion into North and West Africa. Changing patterns in precipitation, especially precipitation in dry and warm seasons, urbanization, human population, livestock density, and climate change exacerbated the geographic expansion of vectors and ecological risk for arbovirus presence. While the ecological risk to arbovirus presence was currently higher in rural areas, our projections indicated a potential future shift towards urban areas. Our study describes how ecological changes are shaping current and future ecological risk of neglected arboviral diseases in Africa and provides spatial maps to aid intersectoral targeted surveillance and vector control as part of early-warning systems.

Background Sindbis virus (SINV) and Batai virus (BATV) are emerging zoonotic arboviruses with a growing number of detections in Europe. Recent SINV outbreaks in northern Europe and high BATV seroprevalence in sheep, goats, and cattle in Germany emphasise the threat they pose to both animal and human health. Despite their presence in countries of similar latitude and climate, neither of these viruses have been detected in the UK. Methods Zoos are strategic sentinel sites for disease surveillance because they are well monitored and possess a high diversity of animal species. Located in southeast England, where the climate and vector prevalence may provide suitable conditions for viral emergence, London Zoo was selected as the sampling site for SINV and BATV prevalence in mosquito samples between September 2022 and January 2024. In 2020, it was also the first location where Usutu virus was detected in the UK. Adult mosquitoes were collected during host-seeking and overwintering seasons while larvae were collected in the summer months. Results A total of 8477 mosquito specimens were analysed, representing all mosquito stages, i.e. including host-seeking and overwintering mosquitoes as well as adults that had emerged from larvae. Mosquitoes of the Culex pipiens / Culex torrentium complex were the most abundant, accounting for 97.5% of the total. Molecular analysis using quantitative polymerase chain reaction was performed to test for SINV and BATV; however, none of the samples tested positive. Conclusions These results suggest that neither SINV nor BATV actively circulated in the sampled area during the study period. The findings provide baseline data for arbovirus surveillance in the UK, particularly at London Zoo, which is home to diverse bird populations that might be potential sentinel populations for viral emergence. Future studies that obtain molecular and serological data on birds or mammals housed at the zoo would complement our surveillance efforts on the emergence or prevalence of SINV and BATV in the UK. This study focused on a single location, but extending sampling and monitoring to other sites across the UK, especially in the southeast, is crucial to strengthening the UK’s preparedness and response strategies in case SINV and BATV emerge in the country in the future.

Polyarthritis and rash caused by Sindbis virus (SINV), was first recognised in northern Europe about 50 years ago and is known as Ockelbo disease in Sweden and Pogosta disease in Finland. This mosquito-borne virus occurs mainly in tropical and sub-tropical countries, and in northern Europe it is suggested to cause regularly reoccurring outbreaks. Here a seven-year cycle of SINV outbreaks has been referred to in scientific papers, although the hypothesis is based solely on reported human cases. In the search for a more objective outbreak signal, we evaluated mosquito abundance and SINV prevalence in vector mosquitoes from an endemic area in central Sweden. Vector mosquitoes collected in the River Dalälven floodplains during the years before, during, and after the hypothesised 2002 outbreak year were assayed for virus on cell culture. Obtained isolates were partially sequenced, and the nucleotide sequences analysed using Bayesian maximum clade credibility and median joining network analysis. Only one SINV strain was recovered in 2001, and 4 strains in 2003, while 15 strains were recovered in 2002 with significantly increased infection rates in both the enzootic and the bridge-vectors. In 2002, the Maximum Likelihood Estimated infection rates were 10.0/1000 in the enzootic vectors Culex torrentium/pipiens, and 0.62/1000 in the bridge-vector Aedes cinereus, compared to 4.9/1000 and 0.0/1000 in 2001 and 0.0/1000 and 0.32/1000 in 2003 Sequence analysis showed that all isolates belonged to the SINV genotype I (SINV-I). The genetic analysis revealed local maintenance of four SINV-I clades in the River Dalälven floodplains over the years. Our findings suggest that increased SINV-I prevalence in vector mosquitoes constitutes the most valuable outbreak marker for further scrutinising the hypothesized seven-year cycle of SINV-I outbreaks and the mechanisms behind.

Babanki virus is a subtype of the Sindbis virus, a widespread arthropod-borne alphavirus circulating in Eurasia, Africa, and Oceania. Characterized by rashes and arthritis, clinical infections due to Sindbis were mainly reported in Africa, Australia, Asia, and Europe. However, its sub-type, Babanki virus, was reported in Northern Europe and Africa, where its epidemiology potential remains poorly understood. The diagnosis of alphaviruses is mainly based on serological testing and conventional PCR methods, which have considerable limits. In this study, we developed a real-time qRT-PCR assay for the detection of Babanki virus. The analytical sensitivity and specificity of the newly established assay were evaluated using in vitro standard RNA and related viruses relevant to the African context, respectively. In addition, its diagnostic sensitivity was assessed using a subset of Babanki virus-positive and -negative mosquito pools collected from the field. The new real-time qRT-PCR assay exhibited a 100% specificity, a 95% detection limit of 1 RNA molecule/reaction, and a diagnostic sensitivity of up to 120 pfu/reaction. This newly established assay could be useful not only for the detection of Babanki virus during epidemics but also in future experimental and surveillance studies focusing on their epidemiology and pathogenicity.