West Nile Virus Spreads Across Europe 

With no human vaccine, mosquito monitoring and early detection are vital 

West Nile virus has caused 77 confirmed human cases and five deaths in Andalucía this year.  European health authorities are warning that the infection is circulating further north and are calling for sustained surveillance and mosquito control.  It is part of the Flaviviridae family, which includes other viruses like dengue and yellow fever. 

While most people tend to experience mild flu-like symptoms, the disease can cause encephalitis or meningitis.  So far in southern Spain there have been 43 cases of mild illness and 34 of neuroinvasive disease.  Sevilla province accounts for most infections, with 65 confirmed cases, followed by Huelva with nine, Cádiz with two and Málaga with one.   

The local clustering underlines the importance of surveillance in identifying where preventive action is needed.  Andalucía combines human case detection with monitoring of mosquitoes and animals.  The area has sited 120 regional mosquito traps, with information from other authorities and research organisations bringing the total to around 215 monitoring sites.  Testing captured mosquitoes helps establish where the virus is circulating and informs local risk assessments, creating alerts before a human infection is identified.   

Municipalities placed under alert are obliged to intensify surveillance and mosquito control, alongside disseminating public information.  Measures extend to identified breeding sites and adult mosquito refuges within 1.5km of populated areas.  This approach connects public health, veterinary and environmental expertise, allowing authorities to respond to evidence of transmission in particular locations. 

Expansion into northern Europe 

As summers become hotter and more prolonged, the European Centre for Disease Prevention and Control (ECDC) reports that West Nile virus is reaching new areas further north.  Up to  mid October there have been 59 human cases in the Netherlands and 15 in Belgium, including the first locally acquired human infections documented in Belgium.  Across EU countries, 1,715 locally acquired cases and 130 deaths have been reported since the beginning of the month.   

Mosquitoes capable of transmitting West Nile virus are already present in England.  UK Health Security Agency (UKHSA) guidance identifies established populations of Culex modestus around the Thames Estuary, Cambridgeshire Fens and parts of the south coast.  Fragments of West Nile virus genetic material were also identified in native Aedes vexans mosquitoes collected in Nottinghamshire in July 2023 although there were no locally acquired human cases. 

West Nile virus circulates mainly between birds and mosquitoes, with infected mosquitoes sometimes transmitting it to people and horses.  Older adults and people with weakened immune systems face greater risk of severe illness and there is currently no vaccine for human use or specific antiviral treatment. 

Personal protection includes mosquito repellent, long clothing, window screens and removing standing water.  For health authorities, the continuing cases in Andalucía and expansion further north reinforce the need to connect mosquito testing and clinical diagnosis, supporting earlier intervention as the pattern of transmission changes.