Outbreak Overview: Andalusia as the Epicenter
According to the latest reports, the West Nile Virus (Virus del Nilo Occidental) outbreak in Spain is severe, with a total of 20 confirmed infections nationwide. Andalusia has reported 19 of these cases, making it the center of the outbreak, with the remaining case found in Extremadura. Among all cases, five patients are in critical condition.
This week, an 82-year-old man from Dos Hermanas in Andalusia unfortunately died from the virus. His condition was exacerbated by underlying health issues.
Environmental Factors: Rice Paddies and Mosquito Breeding
Experts analyze that the abundant rainfall this winter and spring, followed by sustained high temperatures, has created perfect breeding conditions for the virus-transmitting mosquitoes. Researchers from the Spanish National Research Council (CSIC) point out a direct link between mosquito populations and virus transmission, especially in rice-growing areas. For example, the Bajo Guadalquivir region in the province of Seville, with its approximately 36,000 hectares of rice paddies, has become an ideal breeding ground for the primary vector mosquito, Culex perexiguus, due to large, long-standing bodies of water.
In these areas, researchers have captured up to 5,000 female mosquitoes in a single trap in one go, a stark contrast to the fewer than 5 typically caught in urban environments. Besides Seville, the La Janda region in the province of Cádiz and parts of the rice-growing areas in Extremadura are also at high risk.
History and Trends: Climate Change Fuels Northward Expansion
According to CSIC researcher Jordi Figuerola, West Nile Virus is not native to Spain. It was first introduced around 2003 through migratory birds. Studies have identified at least six to seven separate introduction events of the virus.
Climate change is a key driver behind the expanding range of the virus. Global warming leads to milder winters, allowing more female mosquitoes to survive and extending their breeding season, which in turn increases the risk and duration of virus transmission. This trend is not limited to southern Spain; in recent years, the virus has spread northward to the Netherlands and Belgium, with cases even reported in cities like Paris and Moscow.
Control Measures and Historical Review
In response to the outbreak, local governments have activated emergency protocols. In the hardest-hit province of Seville, 20 municipalities, including the city of Seville and Dos Hermanas, are on alert. They have intensified mosquito control and surveillance efforts, with some areas having started control measures as early as March.
Looking back at historical data, about 20 people have died from West Nile Virus in Spain since 2020. Of these, 2024 was the most severe year on record, resulting in 11 deaths. Manuel García Howlett, Director General of the Spanish National Association of Environmental Health Companies (ANECPLA), emphasizes the need for a ‘prevention-first’ strategy. This involves controlling mosquito populations through continuous monitoring before they become a public health threat, rather than reacting passively after cases appear.
