West Nile Virus Cases in European Countries: Heat Map Analysis of Spread, Hotspots & Risk

What Is West Nile Virus — And Why Is Europe Paying Attention?

West Nile Virus (WNV) is a mosquito-borne flavivirus that cycles primarily between birds and Culex mosquitoes. Humans are incidental hosts — infected by the bite of a mosquito that previously fed on an infected bird. It sounds straightforward, but the epidemiology is not.

First identified in Uganda in 1937, the virus spent most of the 20th century confined to Africa, the Middle East, and parts of Asia. Then it moved. By 1999 it had reached North America; by the 2000s, southern Europe started reporting sporadic outbreaks. Today, it is firmly endemic across a swathe of Mediterranean and Eastern European countries — and it’s spreading northward and westward faster than most public health models had predicted.

The concern isn’t trivial. While around 80% of infections are completely asymptomatic, approximately 20% develop West Nile fever — headache, fatigue, muscle aches. The serious worry is the neuroinvasive form: encephalitis, meningitis, acute flaccid myelitis. That affects roughly 1% of all infected people, but in the elderly and immunocompromised, the consequences can be severe or fatal.

Europe’s exposure is deepening. The 2024 season recorded 1,436 locally acquired human cases across 19 countries — well above the previous decade’s mean monthly count, according to ECDC surveillance data. The question isn’t whether WNV is a European public health concern. It clearly is. The question is how the geography of risk is shifting, and what the heat map tells us.

Which European Countries Have the Most West Nile Virus Cases?

West Nile Virus Cases in Europe (2024 Season Data Overview): Record Numbers Across 19 Countries

The European Centre for Disease Prevention and Control (ECDC) tracks WNV human infections through TESSy — the European Surveillance System — collecting case reports from EU/EEA member states and several neighboring countries including Albania, Serbia, and Türkiye. Data are published in weekly epidemiological updates between June and November, with end-of-season summaries thereafter.

The 2024 transmission season ran from March 1 through late October — a notably early start for WNV activity. As of December 4, 2024, ECDC had confirmed 1,436 locally acquired human cases with known place of infection, alongside 125 deaths, across 19 reporting countries. That’s a significant jump from the 802 cases recorded at the equivalent point in 2023.

2024 WNV Season: Country-by-Country Case Count

Source: ECDC Surveillance Data, as of December 4, 2024. Note: Poland reported one probable locally acquired case — not included in the table above as exact place of infection was not reported to ECDC.

Reading the Heat Map: Where the Virus Concentrates and Where It’s Moving

How to Interpret WNV Heat Map Intensity

A West Nile Virus heat map for Europe uses color gradients to represent case density — the darker or more saturated the color over a region, the greater the concentration of confirmed human infections per unit area or population. ECDC publishes these maps seasonally at subnational level (NUTS 3 regions), allowing precise identification of transmission zones.

Pale or near-white areas indicate low or zero confirmed local transmission — either genuinely WNV-free zones or areas with minimal mosquito vector pressure. Light orange or yellow shadings represent sporadic or low-level transmission. Deep red, dark orange, and crimson zones signal dense, sustained outbreak activity.

Primary Hotspots: Southern and Eastern Europe

The heat map’s most intense zones consistently cluster in the Po Valley and Veneto regions of northern Italy, the Attica region and northern Greek lowlands, the Pannonian Basin spanning Hungary and northern Serbia, and Romania’s Danube delta and floodplain provinces.

These areas share several environmental features: large wetland systems or irrigation networks, warm summers with minimal rainfall (concentrating water sources), abundant Culex pipiens mosquito populations, and high densities of migratory and resident bird species that maintain the virus in its enzootic cycle.

Spain’s Andalusia and Extremadura regions have emerged as notable hotspots in recent years — a shift captured clearly in the 2024 map, with 138 cases versus just 19 in all of 2023. The Guadalquivir wetlands, particularly Doñana National Park, provide ideal amplification conditions.

Expanding Frontiers: Central and Western Europe

A consistent trend across multiple ECDC seasons is the northwestward creep of the hot zone. Austria, Germany, France’s Rhône corridor, and Slovakia are appearing on heat maps that were largely blank a decade ago. Germany recorded its first confirmed locally acquired human cases in 2019. By 2024, it was reporting 27 cases with active blood donor nucleic acid testing in place.

The heat map makes one thing visually unmistakable: WNV is no longer a southern European problem. It’s a continental one — and the warm zone is moving north.

Country-Level Analysis: Trends, Spikes, and Year-on-Year Changes

Italy: Consistent Epicenter With Shifting Geography

Italy has led European case counts in most recent seasons, and 2024 was no exception — 455 cases, 21 deaths, and activity distributed across Lombardy, Emilia-Romagna, Veneto, Sardinia, and parts of the south. The country has reported WNV cases in human populations since 2008, with major outbreak peaks in 2018 and again in 2022.

The Italian surveillance system, coordinated through the Istituto Superiore di Sanità (ISS), includes active entomological monitoring and blood donor NAT (nucleic acid testing) screening during transmission season — measures credited with averting several transfusion-related transmission events.

Greece: High Case Burden, Highest Death Toll

Greece reported 217 cases and 34 deaths in 2024 — the highest fatality count of any individual country that season. The northern Greek regions, particularly Macedonia and Thessaly, have been consistently affected since a large 2010 outbreak that prompted significant national surveillance upgrades.

The severity of Greek outcomes likely reflects multiple factors: high proportions of neuroinvasive disease, an older rural population with lower healthcare access in affected areas, and the particular virulence of WNV lineage 2 strains circulating in southeastern Europe.

Albania: Historic Outbreak in 2024

Perhaps the most striking entry in the 2024 data is Albania — 106 cases and 13 deaths, representing the largest WNV outbreak ever recorded in the country. Albania had not reported human WNV cases for the previous four to five years. This kind of re-emergence after a period of apparent quiescence is a documented WNV pattern: the virus can circulate at low levels in bird and mosquito populations for years before favorable conditions trigger human spillover.

Germany and Central Europe: The Northward Expansion in Real Time

Germany’s trajectory illustrates how rapidly the WNV front can shift. Zero locally acquired human cases before 2019. By 2024: 27 confirmed cases, active national blood donor screening protocols, and regular ECDC reporting. The virus was detected in mosquito and bird populations in eastern German states — primarily Brandenburg, Saxony, and Saxony-Anhalt — before human cases appeared.

Austria (34 cases in 2024) and Slovakia (6 cases, first in several years) follow a similar pattern. These are not outliers; they represent the predictable northern expansion of a virus whose vector range is responding directly to climate shifts.

Year-on-Year Comparison: West Nile Virus Cases (Locally Acquired)

Note: Historical figures are approximate based on ECDC annual summaries. 2024 data reflects reported cases up to December 4, 2024.

WNV Cases vs Deaths Scatter Plot (Europe)

What’s Driving the Spread? Climate, Mosquitoes, and Human Factors

Climate Change: The Overarching Driver

A landmark 2024 study published in Nature Communications (Erazo et al., Spatial Epidemiology Lab) formally evaluated the causal link between climate change and WNV’s spatial expansion in Europe — controlling for land-use changes and human population shifts. The findings were unambiguous: current WNV hotspots in southeastern Europe are most likely attributable to climate change, and the population at risk has grown substantially, partly driven by warming trends.

The mechanism is relatively direct. Culex mosquitoes require temperatures above roughly 14–15°C to sustain the extrinsic incubation period of WNV. Warmer, longer summers mean longer transmission windows, faster viral replication within the mosquito, and expanded geographic range for viable vector populations. Extended autumn warmth in 2024 contributed to an unusually protracted season.

Research published in The Lancet Regional Health — Europe (2024) further quantified the short-term meteorological effects on West Nile neuroinvasive disease, confirming that both elevated temperature and specific precipitation patterns are significant predictors of human case counts — and suggesting that climate-informed early warning systems are technically feasible.

Looking ahead, a modeling study published in One Health (Farooq et al., 2023) projected a potential five-fold increase in WNV outbreak risk for parts of Europe by 2040–2060 under higher emissions scenarios. The proportion of European land area reporting WNV could increase from roughly 15% to 23–30%, putting between 161 and 244 million people at risk — up significantly from current exposure levels.

Mosquito Population Dynamics and Culex Biology

The primary bridge vector in Europe is Culex pipiens, a highly adaptable mosquito species that thrives in a range of habitats from wetlands to urban storm drains. Unlike many vector species, Culex pipiens does not require pristine habitat — it tolerates polluted, stagnant water quite well.

Temperature directly governs population dynamics: longer warm seasons extend breeding activity, increase biting frequency, and shorten the viral replication period within the mosquito gut. Moderate precipitation — enough to create water bodies, not enough to flush them — creates near-ideal amplification conditions. This is partly why the 2024 season started so early (cases from March) and extended through late October.

Urbanization and Water Stagnation

Urban and peri-urban expansion creates mosquito breeding microhabitats at scale: clogged gutters, ornamental ponds, abandoned containers, poorly maintained pools and drainage systems, construction water pools. Cities with aging water infrastructure — common across parts of southeastern Europe — inadvertently amplify vector populations year-round.

The interplay between urbanization and WNV is not straightforward — dense urban cores can sometimes dilute transmission if bird reservoir populations are lower — but peri-urban fringes, where human populations mix with agricultural wetlands and poorly managed water infrastructure, are consistently high-risk zones on European heat maps.

Migratory Birds and Cross-Border Transmission

Birds are the reservoir hosts that amplify WNV and carry it across geographic boundaries. Major migratory flyways through Europe — the East Atlantic, Mediterranean, and Black Sea flyways — traverse most of the current hotspot regions. Spring and autumn migrations correspond with the periods of highest enzootic activity.

Cross-border transmission is effectively impossible to prevent through national measures alone. A virus amplified in bird populations in sub-Saharan Africa can arrive in a Greek wetland with the same migratory birds that have made the journey annually for millennia. This is why regional coordination — through ECDC, EFSA joint reporting, and bilateral veterinary surveillance — matters enormously.

Public Health Response: Surveillance, Screening, and Mosquito Control

ECDC Surveillance Architecture

ECDC coordinates pan-European WNV surveillance through TESSy, publishing weekly epidemiological maps from June through November and end-of-season analytical summaries. The system integrates human case data with animal (equid and bird) outbreak notifications from the European Food Safety Authority (EFSA), providing a One Health view of transmission dynamics.

This multi-species surveillance is epidemiologically important: bird die-offs and equine infections often precede human case spikes by days to weeks, giving public health authorities a narrow but real early warning window.

Blood Safety and Donation Screening

Transfusion-transmitted WNV infection is a documented risk. The ECDC recommends that blood establishments implement either a 28-day donor deferral period for individuals who have visited or reside in affected areas, or individual donation nucleic acid testing (ID-NAT) of prospective donors during transmission season. Germany introduced mandatory NAT screening following its first autochthonous human cases in 2019, and has reported no transfusion-transmitted WNV infections since implementing the protocol.

Italy and Greece have established seasonal NAT screening programs in high-risk regions. Harmonizing these protocols across EU member states remains an ongoing regulatory and logistical challenge, particularly as the affected geographic area expands year on year.

Vector Control and Environmental Interventions

National and local authorities in affected countries deploy a range of mosquito control measures: larval source reduction (eliminating standing water), biological larviciding with Bacillus thuringiensis israelensis (Bti), and adult mosquito spraying in high-transmission zones. Several Italian and Greek municipalities operate integrated vector management programs coordinated with regional health departments.

Public awareness campaigns — advising residents to wear repellent, eliminate standing water, use window screens, and avoid peak mosquito hours at dusk and dawn — are rolled out during transmission season. Their effectiveness is difficult to quantify but broadly considered a low-cost, scalable component of outbreak response.

No Human Vaccine — A Critical Gap

It bears stating clearly: as of the 2024 transmission season, no vaccine against WNV has been approved for human use. Veterinary vaccines are available and used for horses — an economically significant incidental host. Treatment for human WNV disease is supportive only; there are no approved antivirals specific to the virus. This gap underscores the importance of prevention — vector control, surveillance, and blood safety screening — as the primary available tools.

WNV Transmission Seasonal Timeline for Europe

Who Is Most at Risk? Severity, Fatality, and Vulnerable Populations

Clinical Spectrum of WNV Infection

The clinical picture of WNV infection in humans spans a wide range. Approximately 80% of infections are completely asymptomatic — detected only incidentally through blood donor screening or serosurveys. Around 20% develop West Nile fever: a self-limiting febrile illness with headache, myalgia, and sometimes a transient rash, typically resolving within a week.

The serious clinical concern is West Nile neuroinvasive disease (WNND) — meningitis, encephalitis, or acute flaccid myelitis — affecting roughly 1% of all infected individuals. Among patients with neuroinvasive disease, the case fatality rate is approximately 10%, though it is substantially higher in older adults and immunocompromised patients. In Italy’s 2024 season, the case fatality rate among neuroinvasive disease cases reached approximately 15%, consistent with rates observed in prior severe years.

Long-term neurological sequelae are common in WNND survivors — fatigue, cognitive impairment, motor deficits — affecting a substantial proportion of those hospitalized. Some research suggests cognitive effects that can mimic early neurodegenerative disease presentations.

Risk Stratification by Population Group

Risk stratification based on CDC, ECDC clinical guidance, and peer-reviewed literature. Individual outcomes vary.

People living in or traveling to endemic regions — particularly in southern and eastern Europe between July and October — face higher exposure risk. Outdoor workers in agricultural or wetland environments, and residents near irrigation infrastructure, face disproportionate mosquito exposure.

Conclusion: What the Heat Map Tells Us — and What Comes Next

The 2024 West Nile Virus heat map for Europe isn’t a picture of a contained, regional disease. It’s a document of ongoing geographic and epidemiological transformation. The deep-red zones across northern Italy, Greece’s lowland provinces, Hungary’s Pannonian basin, and Romania’s Danube floodplain represent well-established transmission corridors. But the expanding orange and yellow shading across Albania, Spain’s Andalusia, Germany’s eastern states, and Austria signal a continent whose WNV map is being redrawn in real time.

The 2024 season — 1,436 cases, 125 deaths, 19 affected countries, Poland recording its first probable locally acquired case — is above the ten-year mean. It isn’t yet the worst year on record (2018 holds that distinction with over 2,100 cases by an equivalent date), but the trajectory is concerning: more countries, earlier season onset, and notable re-emergence in nations that had been case-free for years.

Climate change sits at the center of this story. Research published in Nature Communications in 2024 formally established the causal link between long-term warming and WNV’s spatial expansion in Europe, identifying current southeastern European hotspots as likely attributable to climate-driven shifts in ecological suitability. Projections under mid-to-high emissions scenarios suggest the affected population at risk could reach 161 to 244 million by mid-century.

The public health apparatus — ECDC’s surveillance architecture, national blood screening programs, vector control investments, and One Health coordination with EFSA on animal disease monitoring — is more capable than it was a decade ago. But there are real gaps: no approved human vaccine, inconsistent cross-border harmonization of blood donor screening protocols, and uneven vector control capacity across affected member states.

For clinicians, the practical message is straightforward: during summer and early autumn, West Nile neuroinvasive disease should be on the differential for any unexplained febrile encephalitis or meningitis in a patient with recent exposure history in an affected region. Arboviral panels should be integrated into standard diagnostic workups — a recommendation increasingly echoed in critical care literature as ICU admissions from WNV neuroinvasive disease rise.

For the public, the guidance is simpler: repellent, protective clothing at dusk and dawn, elimination of standing water. Mundane interventions — but meaningful ones when the mosquito carrying the virus is right outside.

West Nile Virus in Europe is no longer an emerging threat. It has emerged. The heat map, updated season by season, tells a story of a continent adapting — imperfectly, incrementally — to a viral reality that is not going away.

References & Data Sources

All data and findings cited in this article are attributed to peer-reviewed literature, official public health agencies, and surveillance systems.

• European Centre for Disease Prevention and Control (ECDC). West Nile Virus Historical Data — Transmission Seasons 2011–2024. https://www.ecdc.europa.eu/en/west-nile-fever/surveillance-and-disease-data/historical
• ECDC. Epidemiological Update: West Nile Virus Transmission Season in Europe, 2023. TESSy Surveillance System.
• Erazo, D. et al. (2024). Contribution of climate change to the spatial expansion of West Nile virus in Europe. Nature Communications. DOI: 10.1038/s41467-024-45290-3
• Farooq, Z. et al. (2023). European projections of West Nile virus transmission under climate change scenarios. One Health. DOI: 10.1016/j.onehlt.2023.100509
• The Lancet Regional Health – Europe (2024). Short-term effect of temperature and precipitation on the incidence of West Nile Neuroinvasive Disease in Europe. DOI: 10.1016/S2666-7762(24)00318-1
• CDC. Clinical Signs and Symptoms of West Nile Virus Disease. https://www.cdc.gov/west-nile-virus/hcp/clinical-signs/index.html
• ECDC. Factsheet about West Nile Virus Infection. https://www.ecdc.europa.eu/en/west-nile-fever/facts
• EEA Climate-ADAPT. West Nile Fever Factsheet. https://climate-adapt.eea.europa.eu/en/observatory/evidence/health-effects/vector-borne-diseases/west-nile-fever-factsheet
• PMC (2025). West Nile virus and arboviral threats: a call for integration into critical care preparedness. PMC12395766
• PMC (2025). Assessment of WNV screening in blood donors, Germany, 2020–2023. PMC11869365
• MDPI Microorganisms (2024). West Nile Virus: An Update Focusing on Southern Europe. DOI: 10.3390/microorganisms12122623