Nearly half of the 69 people infected with West Nile virus in Andalusia this season required hospital admission, health authorities in southern Spain confirmed.
Three of the 34 hospitalized patients have died from the mosquito-borne illness, with the majority of all recorded cases concentrated in the province of Seville. The resurgence follows a quiet summer in 2025 when the region recorded virtually no infections.
Medical research indicates that roughly 80 percent of individuals infected with West Nile virus show no symptoms, while 20 percent develop mild symptoms and only 1 percent suffer severe neuroinvasive illness. However, figures from the Andalusian Ministry of Health show that 30 of the region's 69 cases involved severe neurological complications, representing 43.4 percent of detected infections, alongside 39 mild cases.
Ulises Ameyugo, deputy director of Health Protection at the General Secretariat of Public Health and Health Promotion, said the high proportion of severe cases did not indicate underreporting. Instead, he explained that national and European surveillance protocols focus primarily on detecting cases with neurological involvement.
Ameyugo noted that while targeting severe illness identifies critical cases, it does not record the full extent of virus circulation across the population. To address this gap, the regional health department expanded its monitoring framework last year to track asymptomatic cases and gain a broader overview of local transmission.
Hospitalization trends and clinical symptoms
Patients developing neuroinvasive forms of the infection account for most hospital admissions in the region. Ameyugo stated that encephalitis has been the most common clinical manifestation among hospitalized patients, followed by meningitis.
The health official urged calm, emphasizing that the risk of developing severe complications remains highest among elderly individuals and patients with pre-existing medical conditions.
West Nile virus is a mosquito-borne flavivirus transmitted primarily to humans through the bites of infected Culex mosquitoes, which acquire the virus after feeding on infected wild birds. While most human cases resolve without treatment, severe neuroinvasive disease can cause acute brain inflammation, long-term neurological damage, or death.
Andalusia, an autonomous community in southern Spain with a population of over eight million, features extensive river basins such as the Guadalquivir, where warm wetland environments create ideal breeding conditions for mosquito populations during summer and autumn months.
Comparison with previous outbreaks
Conditions ahead of the 2026 season had raised concerns of a potential surge similar to the severe outbreak in 2024, which recorded more than 100 cases and 11 deaths. Heavy rains prior to spring combined with a mild winter created favorable breeding conditions for mosquitoes across the region.
Despite those environmental factors, Ameyugo pointed out that the overall impact on case numbers to date has remained lower than during the major outbreaks of 2020 and 2024, based on comparative data for neurological cases.
Following the 2024 outbreak, the Regional Government of Andalusia reinforced its surveillance program by introducing early anticipation and control measures. These actions were carried out in coordination with provincial councils and municipal authorities to manage mosquito populations effectively.
Monitoring broader vector-borne diseases
Regional health authorities have expanded their scope beyond West Nile virus to address a broader range of vector-borne diseases. Officials noted that rising global temperatures, climate change, international travel, and tourism are driving an increase in mosquito-transmitted illnesses across the Northern Hemisphere.
As part of these preventive efforts, Andalusia has launched active surveillance for the tiger mosquito across more than 350 municipalities. Health authorities have also established specific response protocols for imported cases of dengue, Zika, and Chikungunya to prevent localized transmission.
Ameyugo confirmed that no local or autochthonous cases of dengue, Zika, or Chikungunya have been detected in Andalusia to date, maintaining that current control measures remain focused on preventing local establishment.
