Italy Reports Majority of West Nile Virus Cases in 2025 Outbreak

According to a surveillance report from The European Centre for Disease Prevention and Control, 202 locally acquired cases of West Nile virus infection have been reported in 6 countries. This is for the period up until August 6, 2025. More cases have been notified since this report.

The majority have occurred in Italy (168). Cases have also been reported in Greece (26), France (3), Romania (3), Bulgaria (1) and Hungary (1). There have been 10 deaths.

The provinces of Latina and Frosinone, in the Lazio region of Italy, are the most affected.

While the number of cases is above the ten-year average it is still below the number of notifications observed in 2018 and 2024.

Favourable environmental conditions for mosquitos have contributed to the increase in cases. The season of risk is also longer with cases being detected in northern Italy as early as March.

West Nile Virus has been present in Europe for more than 20 years. The first major outbreak was reported in Romania in 1996, followed by significant events in Greece and Italy from 2010.

What is West Nile Virus (WNV) ?

West Nile virus (WNV) is a vector-borne disease. It is a viral infection transmitted by the bite of an infected mosquito. Mosquitoes carry the virus after feeding on infected birds and transmit the disease to humans and other animals.

Symptoms and severity

Studies show that 8 in 10 infected people are asymptomatic (experience no symptoms), 1 in 5 infected people develop a mild flu-like illness. Symptoms can include fever, headache, tiredness, muscle aches, nausea, vomiting, and a rash.

1 in 150 people infected with WNV will develop more severe disease (WHO, 2017), such as encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord) (CDC, 2023).

Recovery from severe illness may take several months. Among those who experience severe central nervous system illness, 1 in 10 people have a fatal outcome.

Travel risk and seasonality

Anyone who resides in or travels to regions with WNV activity is at risk of infection. In tropical climates, cases occur throughout the year.

In Europe, the United States and other temperate Northern Hemisphere climates, WNV occurs through June and November, peaking around July and September. Outbreaks often follow major bird migratory routes.

In the U.S., WNV is endemic (native) in New York State, and is considered a seasonal infection, with cases peaking in some parts of the state each Summer.

Travellers returning from affected regions who develop a high fever, muscle weakness or neurological symptoms are advised to seek immediate medical attention and mention possible exposure to West Nile virus.

Individual risk factors

While most West Nile virus infections are mild or asymptomatic, certain groups are more likely to develop severe disease.

• Those over the age of 50 years are at higher risk for severe illness, however, serious infections can occur in people of any age (WHO, 2017).
• Immunocompromised people, for example, people living with HIV or transplant recipients, are at the highest risk for becoming severely ill with WNV infections (ECDC, 2023).
• Those with underlying illnesses, such as diabetes, cancer, and kidney disease, are also associated with more severe disease.

West Nile Virus precautions and prevention

The species of mosquito responsible for the vast majority of WNV transmission to humans is the Culex species. These mosquitoes are mainly active during the evening, but their peak activity occurs at dusk and dawn.

The best way to prevent infection is to protect yourself against mosquito bites.

Italian health authorities have stepped up mosquito surveillance and control measures in affected provinces and public advisories have been issued to reduce exposure to bites.