Andalusia confirms 16 West Nile virus cases, all in Seville province, as 19 municipalities enter alert

Rising cases in Seville province

Andalusia has confirmed 16 human cases of West Nile fever so far in 2026, every one of them in the province of Seville. The two most recent infections, both mild, were announced on 3 August: a man from Villamanrique de la Condesa and a woman from Coria del Río. They join a cluster that now includes 11 mild cases and five neuroinvasive cases, the latter requiring hospitalisation. The regional health ministry said the diagnoses were confirmed by the reference laboratory at the Virgen del Rocío University Hospital in Seville.

Earlier in the same week, a man from Dos Hermanas was hospitalised with meningoencephalitis caused by the virus, and a case was confirmed in La Puebla del Río. The Dos Hermanas patient remained in hospital as of 3 August. The municipality was declared an alert area until 30 August, while Villamanrique de la Condesa and Coria del Río were placed under alert until 26 and 27 August respectively.

Control measures intensified

Across the affected zone, the Diputación de Sevilla has scaled up its vector-control programme to maximum deployment. Eleven treatment units are now working simultaneously in 15 municipalities under special surveillance. In Dos Hermanas alone, between 29 June and 24 July, teams carried out 422 larval inspections, found 149 positive sites, and applied 145 larvicide treatments to eliminate breeding spots before adult mosquitoes emerged. Adulticide fogging from pick-up trucks, using Tifone sprayers, is conducted at night when mosquitoes are most active and public presence is lowest. A further adulticide round was scheduled for the week of 4 August.

Local authorities are inspecting and treating drains, sewer networks, standing water, green spaces, and any other sites that could harbour Culex mosquitoes, the main vector. The alert status requires municipalities to intensify actions not only in built-up areas but also within a 1.5 km radius of identified larval foci or adult resting sites.

Virus circulation and expert analysis

Raúl Rivas, professor of microbiology at the University of Salamanca, explained that Spain has two main foci of West Nile virus. The southwestern focus, centred on Seville, carries lineage 1, while the northeastern focus around the Ebro delta carries lineage 2, the more common European strain. The virus circulates primarily between birds and mosquitoes; humans and other mammals are incidental hosts.

The situation is within what you would expect in Andalusia because the virus is circulating among birds, and we know it particularly affects corvids and raptors.

Nicola Lorusso, director of the Andalusian public-health strategy unit Avista, noted that virus circulation has been detected in mosquito traps or birds in every Andalusian province except Cádiz. He said the apparent rise in human cases is partly due to a new surveillance protocol that now captures mild infections, allowing earlier detection of transmission.

The increase in cases is partly due to the introduction this year of surveillance of mild cases, a measure aimed at identifying virus transmission earlier.

Background and outlook

In 2024, Seville province recorded 102 West Nile cases and two deaths, triggering neighbourhood protests. The following year, only two cases were reported, a drop attributed to a sharp increase in prevention efforts by the provincial government and town councils under an autonomous-community mosquito-control programme. The current 16 cases, while well below the 2024 peak, mark a return of the virus to public attention. Nineteen Andalusian municipalities are now under alert, roughly 80% of them in Seville province, with additional alerts in Jaén, Granada, and Málaga. Viral circulation has also been detected in mosquitoes in Benacazón (Seville) and Bujalance (Córdoba), though no human cases have been confirmed there. Health authorities are urging residents, especially vulnerable people, to use repellents, wear protective clothing, and eliminate standing water around homes.