The Portuguese Council for Health and Environment (CPSA) has issued an alert regarding the high probability that human infections with the West Nile virus are going undetected. This warning comes amid the widespread dissemination of mosquito vectors across Portugal and a significant surge in cases throughout Southern Europe.
According to data from the European Centre for Disease Prevention and Control (ECDC), 2,009 locally acquired human cases were reported between the start of the 2026 transmission season and October 29. These infections were recorded across 20 European countries, representing nearly double the number of cases registered in 2025. While Portugal is not currently listed among countries with notified human cases in the latest ECDC report, the nation has identified four foci of infection in equines this year.
The CPSA highlights that Italy has reported 780 cases so far this year, followed by Greece with 463, France with 180, and Spain with 149. In Spain, infections have been concentrated primarily in Extremadura and Andalusia, regions bordering Portugal. Earlier data from September indicated that Italy alone recorded 51 deaths and 657 confirmed cases, figures that exceed those from the same period last year. Additionally, Spain declared a state of alert in July for the municipalities of La Puebla del Río and Coria del Río in Andalusia after detecting virus-carrying mosquitoes.
The CPSA explains that migratory birds serve as the primary reservoir for the virus, which is transmitted to humans through the bite of infected mosquitoes, particularly those of the Culex genus. These vector species are widely distributed in Portugal. A 2025 report by the National Vector Surveillance Network (REVIVE) noted that Culex mosquitoes accounted for over 45% of a sample of 9,502 adult mosquitoes captured by teams from the National Health Institute Ricardo Jorge (INSA).
While most infected individuals remain asymptomatic, approximately 20% develop febrile illness characterized by headaches, muscle pain, fatigue, nausea, or vomiting. These symptoms can be easily confused with other viral infections. More critically, about 5% of cases develop severe neurological complications, including meningitis, encephalitis, or acute flaccid paralysis. The risk of these severe forms is higher among older adults and immunocompromised individuals.
In response to these risks, the CPSA recommends enhancing training and awareness among healthcare professionals to consider West Nile virus in cases of unexplained febrile syndromes or neurological conditions, depending on epidemiological context. The council also advocates for timely access to laboratory diagnostics nationwide, suggesting confirmation via RNA techniques, particularly in urine samples where the virus remains detectable two to three weeks after infection onset.
Further recommendations include strengthening mosquito surveillance and control measures, as well as informing the public about protection against bites, especially at dusk and during the night. Eliminating standing water that favors mosquito reproduction is also advised. Established in 2022, the CPSA brings together more than 115 members, including health associations, professional orders, scientific societies, academic institutions, pharmaceutical laboratories, research institutes, local health units, patient associations, and municipalities.
Sources: Observador.