A narrative review of climate- and environment-dependent dynamics of vector-borne diseases in the Nordic region: evidence from Finland.

INTRODUCTION: Vector-borne diseases (VBDs) pose a growing threat to human and animal health, driven by complex interactions among and between vectors, hosts, pathogens, and the environment. The Nordic region is warming at twice the global average rate, creating novel ecological conditions that reshape VBD transmission dynamics. OBJECTIVES AND METHODS: This narrative review synthesises current knowledge regarding major tick- and mosquito-borne diseases in the Nordic region, with a focus on Finland, based primarily on outputs from the VECLIMIT project (2020-2023), supported by other Nordic studies. RESULTS: The most prevalent human VBDs are Lyme borreliosis (LB), tick-borne encephalitis (TBE), tularaemia, and Sindbis virus (SINV) infections. Over the past decade, LB and particularly TBE incidence have increased, whereas SINV and tularaemia show cyclical patterns. The principal tick vectors Ixodes ricinus and Ixodes persulcatus are expanding geographically, while key mosquito vectors, Aedes cinereus/geminus and Culex pipiens/torrentium, are widespread. Rising temperatures and extended growing seasons promote vector activity and pathogen development, whereas heterogenous environments, such as wetlands and urban green spaces, support vector and host populations. While small mammals serve as key reservoirs for tick-borne pathogens, cervids drive tick propagation, and avian hosts maintain vector-borne enzootic cycles. Substantial gaps remain in prevention and awareness across public, medical, and veterinary sectors. CONCLUSIONS: Climate warming is likely to increase the spread of many endemic and invasive vectors and pathogens, yet surveillance remains limited and understanding of VBD drivers incomplete. Addressing these gaps requires coordinated One Health frameworks leveraging citizen science and cross-border Nordic collaboration.