Climate Change and Mosquito Vectors

A study published in the journal *One Health* by researchers from the Doñana Biological Station reveals how climate change is altering conditions for WNV propagation in Europe. The research team, led by jordi Figuerola, created distribution maps of the four main mosquito species that transmit the virus—all within the *Culex* genus—and combined this data with their transmission capacity.

The study concluded that southern Europe, particularly Andalusia, southern Italy, and the Balkans, presents optimal environmental conditions for virus circulation. Warmer winters are a key factor, allowing mosquitoes to reproduce and prolonging the transmission season.This extended window increases the risk to humans and animals, especially birds and horses, which are primary hosts of the virus.

The research also warns that even areas with only one mosquito species present are not immune. The adaptability of different species to various environments ensures the virus’s persistence and territorial expansion.

Andalusia: A West Nile Virus hotspot

Andalusia has been identified as a primary hotspot for WNV transmission for several years, a fact well-known to local authorities.

Increased Number of Affected Areas

The latest report from the Integral Surveillance and Control Program of Western Nile Fever, published by the Junta de Andalucía’s Ministry of Health and Consumption, indicates a rise in high-transmission-risk areas within the region.

• Seville is the province with the highest number of localities on alert.
• Cádiz follows closely behind.

High-risk status is assigned to areas where virus circulation has been detected in the past three years or where there is evidence of its presence in the current season, even if it doesn’t meet the criteria for an “Area in Alert.”

Juanjo Sánchez, coordinator of the platform of those affected by the WNV in La Puebla del Río, acknowledged that the Board has improved the prevention and control tasks this year thanks to the neighborhood action. He noted that during the summer of 2024, many riverside villages protested, saying they could not live quietly outside their homes due to the high mosquito presence, which he attributed to a great delay of fumigations that should occur earlier in the year.

The March rains have increased water levels, which Sánchez warns is attracting mosquitoes. He fears the situation could worsen in June when rice cultivation begins, creating extensive flooded areas that attract even more insects.

Seville’s Experience with West Nile Virus

Since the first outbreak in 2020, the West Nile Virus has exhibited fluctuating behaviour in the region.

• 2020: 87 cases and seven deaths, with Coria del Río and La Puebla del Río being the most affected municipalities.
• 2021: Six infections, concentrated in the same locations.
• Subsequent Years: minor presence.
• 2024: 107 confirmed cases and 11 deaths, with Seville accounting for 93 infections.

Ulises Catalan Ameyugo, the deputy director of health protection, stated that we have gone from 20 municipalities at high risk to 103 in this season throughout Andalusia. Though, he believes it is indeed too early to confirm virus circulation, noting that Mosquitoes there is all year, with greater or lesser density depending on the territory, and of different species, in this case we focus on those transmitted by the VNO, whose greatest circulation It starts in May so it is from there when our entomological surveillance system is activated, which this year will be increased by number and extension of mosquito traps.

Regional Breakdown of Risk Levels

• Cádiz: Several municipalities at high risk, especially in the countryside and along the coast, including Jerez de la Frontera, vejer de la Frontera, Barbate, Tarifa, and Medina Sidonia. The presence of wetlands and marshes is a significant factor.
• Córdoba: A clear division between the north (less risk) and the south, with municipalities like Palma del Río, puente Genil, and Lucena at medium or high risk due to proximity to the Guadalquivir Valley and rice fields.
• Huelva: Unequal distribution, with locations near Doñana National Park and Las Marismas, such as Almonte, Moguer, and Gibraleón, at high risk.
• Málaga: Differentiated pattern between the coast (Malaga Capital, Marbella, Fuengirola, and Estepona at medium-high risk) and the interior (mountain range and Axarquía at low levels due to mountainous terrain and fewer wetlands).
• Granada and Jaén: Generally lower risk,but some locations like Atarfe,Pinos Puente,and Santa Fe in Granada,and Andújar,Linares,and La Carolina in Jaén,are at high risk due to nearby rivers and wet areas.
• Almería: The province with the least risk, with no municipality at a high level.

Action Plans and Prevention

Municipalities classified as medium and high risk are implementing action plans that include:

• reduction of mosquito populations in urban and rural areas.
• Supervision of larval and adult density.
• Traps for infected mosquitoes.
• Citizen awareness campaigns starting in May.

With summer approaching, the Andalusian Board is preparing for a critical season in the fight against the Nile virus. Coordination between institutions, early action, and constant surveillance are key to containing the threat.

Institutional coordination and Prevention Measures

Last year’s expansion of the virus was compounded by institutional clashes,particularly with the diputación of seville,as both entities blamed each other for failing to assume fumigation,control,and prevention tasks in a timely manner.

The coordinator of the affected platform lamented this situation, stating, They threw the ball while we paid the price, and criticized the Junta de Andalucía for not assuming its obligation, which he believes was delegated to the deputations. he acknowledged that prevention efforts began in late January this year, earlier then in March 2024.

According to the deputy director of Health Protection,these tasks involve regularly visited to the perhaps affected areas to verify the presence of mosquito larvae of the genre Culex and his density. If necessary, they are treated with biological products. He added, have initiated visits to the municipalities to advise them in their Surveillance and Control Plans since the development of these new lines in areas such as human surveillance or as in health promotion for citizen awareness.

Municipalities with medium and high risk must implement specific plans to reduce mosquito populations and minimize virus transmission. Control measures will be implemented in transited urban and rural areas, along with mosquito density surveillance. High-risk municipalities will have more extensive plans, including entomological supervision through traps to detect infected mosquitoes, and intensified citizen awareness campaigns starting in May.