CPSA alerts Western Nile virus to be unnoticed

O Portuguese Council for Health and Environment (CPSA) today warned of the “high probability” of human infections by the Western Nile virus going unnoticed in the face of the spread of mosquitos throughout the country.

“ The documented circulation of mosquitoes with the virus, the existence of infected animals in the country and the high number of cases registered in southern Europe, particularly in Spain, justify greater attention from health professionals and authorities to the possibility of this underdiagnosis,” the CPSA said.

According to this collaborative network of health-related organizations, Portugal is not among the countries with human cases reported in the latest report of the European Centre for Disease Prevention and Control (ECDC), despite having recorded four outbreaks in equidae this year.

The CPSA pointed out that since the beginning of the transmission period of 2026 and until 29 October 2,009 human cases of locally acquired infection have been reported in 20 European countries, almost twice the cases recorded in 2025.

The statement uses the ECDC report to warn that this year Italy has reported 780 cases, Greece 463, France 180 and Spain 149, mainly in Extremadura and Andalusia, near the border with Portugal.

Data released in September indicated that Italy recorded 51 deaths by the Western Nile virus and 657 confirmed cases, figures that surpass those of the same period last year.

In July, Spain declared a state of alert for the municipalities of La Puebla del Río and Coria del Río, in the region of Andalusia, after mosquitoes carrying the virus were detected.

According to the Portuguese Council for Health and Environment, which aims to minimize the impact of environmental changes on health, the main reservoir of this virus is migratory birds and infection is transmitted to people by the bite of infected mosquitoes, especially the genus Culex.

The various species of this virus are “widely distributed in Portugal”, representing more than 45% of the sample of 9,502 adult mosquitoes captured in 2025 by the teams of the Ricardo Jorge National Health Institute (INSA), according to the report of the National Vector Surveillance Network (REVIVE), the CPSA advanced.

He said, although the vast majority of infected people do not have symptoms, approximately 20% develop febrile disease, with manifestations such as headaches and muscle pain, tiredness, nausea or vomiting, which may be confused with other viral infections.

“However, about 5% develop neurological complications that can be severe, such as meningitis, encephalitis or acute flaccid paralysis,” PCSA said, stressing that the risk of severe forms is higher in older people and immunodepressed people.

The board therefore recommended strengthening the training and sensitization of health professionals to consider this infection with febrile syndromes without clear cause and pictures of meningitis, encephalitis or acute flaccid paralysis, according to exposure and epidemiological context.

It also defended the need to ensure timely access to laboratory diagnosis throughout the country, advising the confirmation of results by RNA techniques, particularly in urine, where the virus is detectable two to three weeks after the onset of infection.

Another of the recommendations is to strengthen the surveillance and control of mosquitoes, as well as the information of the population about the protection against bites, especially at dusk and at night, and the elimination of stopped waters that favor their reproduction.

Created in 2022, CPSA brings together more than 115 members, such as health associations, professional orders, scientific societies, academic institutions, pharmaceutical laboratories, research institutes, local health units, patient associations and municipalities, among others.