The study, published in Virology Journal, focused on Culex pipiens sensu lato and Culiseta annulata, two species that dominate the UK mosquito fauna and are considered among the most plausible vectors should arboviruses such as West Nile or Usutu virus establish local transmission cycles. Between 2021 and 2022, the team collected adult mosquitoes across the grounds of the two zoological collections, sites chosen deliberately because zoos concentrate large numbers of animals in outdoor enclosures where mosquitoes feed readily. That combination of abundant vectors, diverse vertebrate hosts and regular human visitors makes zoological collections potential interfaces for virus exchange between mosquitoes, animals and people, and therefore valuable sentinel locations for surveillance.

In total, 4,042 mosquitoes were processed and sequenced across 44 pools. The researchers extracted total nucleic acids and applied a metagenomic sequencing strategy designed to capture both RNA and DNA viruses, allowing them to recover viral genomes without relying on prior assumptions about which viruses might be present. Bioinformatic assembly and taxonomic classification of the resulting reads yielded 26 viral genomes, a striking haul for a country whose mosquito viromes have remained comparatively understudied. Nine of these represented entirely novel species, distributed across both RNA and DNA virus families, underscoring how much basic viral diversity in northern European mosquitoes still awaits description.

A consistent pattern emerged across the sampling sites: several viruses were detected in every pool analysed, indicating substantial overlap in virome composition between the two zoos. This shared core of viruses suggests that certain mosquito-associated viruses are widespread and stable components of the local mosquito fauna rather than isolated curiosities confined to a single habitat. Such ubiquity matters for risk assessment, because a virus that maintains itself efficiently across geographically separated mosquito populations has, by definition, the ecological flexibility that emergence requires, even if most of these viruses ultimately prove harmless to vertebrates.

The headline findings are two novel orthobunyaviruses, named Atherstone virus and Deva virus, belonging to the family Peribunyaviridae. Orthobunyaviruses are a genus with a serious pedigree: it includes recognised human and animal pathogens such as Schmallenberg virus, which devastated European ruminant farming after its emergence in 2011, and Oropouche virus, a growing public health concern in the Americas. The tripartite RNA genomes of orthobunyaviruses encode a viral RNA-dependent RNA polymerase on the large segment, surface glycoproteins on the medium segment, and nucleoprotein plus accessory proteins on the small segment. Finding two previously unknown members of this genus in British mosquitoes immediately elevates them to candidates for closer scrutiny.

Not all orthobunyaviruses pose equal risk, and the study went beyond simple detection to ask which of the two new viruses resembles a genuine arbovirus, capable of replicating in both mosquitoes and vertebrate hosts. The team employed MosViR, a machine-learning classification tool trained on known mosquito viruses to predict whether a given virus is likely to be mosquito-restricted or arthropod-borne. For Atherstone virus, detected at both zoos, the prediction pointed towards arbovirus status, a result that alone would justify follow-up. More compelling still was the genomic evidence: Atherstone virus carries an open reading frame encoding a non-structural protein S, or NSs, a well-characterised virulence factor in orthobunyaviruses that antagonises host antiviral responses, including the interferon system, and is a hallmark of pathogenic members of the genus.

Deva virus tells a different story. Its small segment lacks an NSs open reading frame altogether, and MosViR did not predict it to be an arbovirus. The absence of NSs, combined with the absence of a vertebrate-infecting signature, is consistent with Deva virus being an insect-specific virus, locked into replication within mosquito cells and their close relatives. Insect-specific viruses of this kind are increasingly recognised as common and sometimes abundant residents of mosquito viromes. Although they do not infect vertebrates directly, they are far from biologically irrelevant: they can modulate mosquito immunity, compete with arboviruses for cellular resources, and in some cases reduce the ability of mosquitoes to transmit pathogenic viruses, making them subjects of interest both for basic virology and for potential interference-based control strategies.

The broader viral inventory recovered in the study reinforces this picture of a layered virome. Alongside the orthobunyaviruses, the sequencing identified viruses spanning multiple families, including flavivirus-like and other RNA virus groups as well as DNA viruses, with several classified as novel species. Distinguishing arboviruses from insect-specific viruses is one of the central analytical challenges in mosquito metagenomics, because both can be present in the same sample and their genomes can be difficult to interpret from sequence data alone. Tools such as MosViR, combined with comparative genomics against reference databases and catalogues of known arboviruses, provide a probabilistic framework for triage, flagging which discoveries warrant experimental characterisation in cell culture and vertebrate systems and which can be provisionally set aside as likely insect-restricted.

Why does this matter for the United Kingdom specifically? The country sits at the northern edge of the range of many mosquito species, and climate warming, changes in land use and the movement of animals and goods are all expected to alter the dynamics of mosquito-borne disease in temperate Europe. Usutu virus has already established itself in British birds and mosquitoes, and West Nile virus circulates periodically in neighbouring countries. Risk frameworks built around these known threats are essential, but the new study argues that they should be complemented by surveillance for the unknown: viruses already resident in local vectors whose properties have never been tested. A virus that today appears to be insect-specific could, through reassortment with a related pathogen or through evolutionary change, acquire new capabilities. Orthobunyaviruses are particularly notable in this respect because their segmented genomes can reassort when mosquitoes are co-infected with related viruses, generating novel combinations with unpredictable host ranges.

The authors are careful not to overstate the immediate danger. Detection of a viral genome in a mosquito does not demonstrate that the virus infects or harms vertebrates, and neither Atherstone nor Deva virus has been shown to cause disease. What the study provides is a prioritised list of candidates and a demonstration of method: that large-scale metagenomic surveillance of UK mosquitoes is feasible, productive and capable of revealing both the diversity of local viromes and the specific viruses that merit laboratory follow-up. Isolation of Atherstone virus, characterisation of its host range, and serological surveys of animals and humans near the sampling sites would be the logical next steps. In the meantime, the work adds the United Kingdom to the growing map of regions where the viruses closest to home, rather than those arriving from abroad, are proving to be the first order of business for emerging infection surveillance.

Subject of Research: Metagenomic surveillance of mosquito viromes at two UK zoos reveals novel mosquito-associated orthobunyaviruses

Article Title: Emergence risks from within? Metagenomic analysis of mosquito viromes from two zoos reveals mosquito-associated orthobunyaviruses in the UK

Article References: Pilgrim, J., Seechurn, N., Cunningham-Oakes, E., Gillespie, L., Dobbs, P., Lopez, J., Kohl, A., Hughes, G. L., Blagrove, M. S. C., Baylis, M., & Darby, A. C. (2026). Emergence risks from within? Metagenomic analysis of mosquito viromes from two zoos reveals mosquito-associated orthobunyaviruses in the UK. Virology Journal. https://doi.org/10.1186/s12985-026-03305-z

Image Credits: AI Generated

DOI: 10.1186/s12985-026-03305-z

Keywords: orthobunyavirus, mosquito, virome, metagenomics, arbovirus, Culex pipiens, Culiseta annulata, surveillance, zoonotic risk, insect-specific virus, United Kingdom, Peribunyaviridae