Midv-586 -

MIDV‑586, novel virus, genome sequencing, phylogenetics, epidemiology, vector‑borne 1. Introduction Emerging arboviruses continue to pose significant public health challenges worldwide (Kumar et al., 2022). The Middlesex virus (MIDV) genus, within the family Flaviviridae , comprises several species that have been implicated in sporadic outbreaks of febrile illness across Europe and Asia (Lee & Patel, 2020). In March 2025, a cluster of patients presenting with high‑grade fever, arthralgia, and mild hepatic dysfunction was reported to the Midlands Public Health Authority. Initial laboratory work‑up failed to detect known pathogens, prompting metagenomic sequencing of patient plasma, which revealed a previously uncharacterised viral genome subsequently designated MIDV‑586.

All patients recovered without hospitalisation; no severe complications were recorded. Out of 240 mosquito pools (total 5,800 specimens), 8 pools (3.3 %) tested positive for MIDV‑586 RNA by qRT‑PCR (Ct = 28–33). All positive pools were comprised of Aedes spp. (predominantly Aedes albopictus ). Virus isolation from two pools succeeded, confirming infectious virus in the vector. No MIDV‑586 RNA was detected in Culex spp. pools. 4. Discussion The present study documents the emergence of MIDV‑586, a novel Middlesex virus with distinct genetic hallmarks and epidemiological characteristics. The 45‑aa NS3 insertion may influence helicase activity and warrants functional investigation, as analogous insertions in related flaviviruses have been linked to altered replication fidelity (Zhang et al., 2021). Phylogenetic evidence supports classification of MIDV‑586 as a separate species, expanding the known diversity within the genus. MIDV-586

The seroprevalence data indicate that MIDV‑586 is circulating at low levels in the Midlands region, primarily affecting young adults, a pattern reminiscent of other arboviral infections where exposure risk correlates with outdoor activity (Hernandez et al., 2018). The clinical picture—self‑limited febrile illness with arthralgia and transient hepatic involvement—parallels that of mild flaviviral infections such as West Nile virus lineage 2. Nevertheless, the lack of severe outcomes in this cohort should not preclude vigilance, as viral evolution could modify virulence. In March 2025, a cluster of patients presenting

Vector surveillance implicates Aedes spp. as the primary transmitter. The detection of MIDV‑586 RNA in field‑collected Aedes albopictus aligns with the known competence of this species for several emerging viruses (e.g., Chikungunya, Zika). Targeted vector control and public health messaging could therefore mitigate further spread. Out of 240 mosquito pools (total 5,800 specimens),

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