TL;DR
- West Nile virus is spread by Culex mosquitoes — the ordinary house mosquitoes that bite from dusk into the night, not the day-biting tiger mosquito behind dengue.
- Around 80% of people infected never develop any symptoms at all. About 1 in 5 get a flu-like illness, and fewer than 1% develop serious neurological disease.
- Risk of severe illness rises sharply with age, particularly over 60, and in people who are immunocompromised.
- Locally acquired cases are reported most summers in Italy, Greece, Romania, Hungary, Spain, France, Austria, Bulgaria, Serbia and neighbouring countries, with the season running roughly from June to November.
- There is no human vaccine and no specific antiviral treatment, so avoiding bites in the evening hours is the whole prevention strategy.
West Nile virus has quietly become a fixture of the European summer. It is not new, it is not exotic, and for the overwhelming majority of people who catch it, nothing at all happens. But it is worth understanding — because the mosquito that carries it lives in ordinary gardens, cities and river valleys across the continent, and because the simple habit that prevents it is the one most people skip.
What is West Nile virus?
West Nile virus is a flavivirus, a relative of dengue and tick-borne encephalitis. Its natural cycle runs between birds and mosquitoes: mosquitoes of the Culex genus feed on infected birds, then pass the virus on when they feed again. Humans and horses are what virologists call dead-end hosts — we can be infected, but we do not carry enough virus to pass it back to a mosquito. That means you cannot catch West Nile virus from another person through everyday contact.
The rare exceptions are medical: the virus can be transmitted through blood transfusion, organ transplantation, and from mother to baby during pregnancy or breastfeeding. This is why blood services in affected regions screen or defer donors during the transmission season.
Which mosquito spreads it, and when does it bite?
The main European vector is Culex pipiens, the common house mosquito. It breeds in stagnant, organically rich water — blocked gutters, water butts, drains, neglected ponds, old buckets — and it feeds mainly between dusk and dawn. That timing is the single most useful thing to know, because it is completely different from the pattern of the tiger mosquito now established in southern Europe, which bites in daylight.
West Nile virus versus dengue in Europe: two different routines
| West Nile virus | Dengue (and chikungunya) | |
|---|---|---|
| Mosquito | Culex pipiens — house mosquito | Aedes albopictus — tiger mosquito |
| Biting time | Dusk, night, early morning | Daylight, peaking morning and late afternoon |
| Breeding sites | Stagnant, dirty water; drains, gutters, ponds | Small clean water pockets; saucers, buckets, gutters |
| Reservoir | Wild birds | Humans |
| Vaccine | None for humans | Restricted eligibility, not routine for travellers |
| Practical priority | Evening and night protection | Daytime protection |
Where in Europe does West Nile virus circulate?
Transmission is concentrated in warm regions with wetlands, river plains and irrigated agriculture — the habitats birds and Culex mosquitoes share. In recent years, locally acquired human cases have been reported from Italy (especially the Po valley), Greece, Romania, Hungary, Bulgaria, Serbia, Spain, France, Austria and Croatia, with occasional detections further north and west as summers warm. The picture changes every year, which is why the ECDC publishes weekly updates through the transmission season rather than a fixed map.
For locals, this means a familiar summer risk that varies by district. For travellers, it means a road trip through northern Italy or a late-summer stay in Greece is a more relevant exposure than the destination sounds.
When is the season?
The European transmission season generally runs from June to November, with most human cases reported in August and September. It ends when temperatures drop and mosquito activity stops. A hot, wet summer followed by a warm autumn tends to extend the season at both ends — one reason the risk period has been creeping longer in parts of central and southern Europe. If you want the wider seasonal picture for the region, our guide to mosquito season in Central Europe covers when activity typically peaks.
What are the symptoms?
Most infections cause nothing. Health authorities estimate that roughly 80% of infected people have no symptoms whatsoever and never know they were exposed.
- No symptoms (around 80%) — infection passes unnoticed.
- West Nile fever (around 20%) — fever, headache, tiredness, body aches, sometimes a rash on the trunk, swollen glands or nausea. It usually resolves in days, though fatigue can linger for weeks.
- Neuroinvasive disease (under 1%) — meningitis, encephalitis or acute flaccid paralysis, with high fever, stiff neck, confusion, tremors, seizures or muscle weakness. This is a medical emergency, and according to the CDC around 1 in 10 people who develop it do not survive.
The incubation period is typically 2 to 14 days after the bite. There is no specific antiviral treatment — care is supportive, and severe cases are treated in hospital.
Who is most at risk?
Severe illness is heavily concentrated in older adults, particularly those over 60, and in people with weakened immune systems, cancer, diabetes, kidney disease or a history of organ transplantation. For a healthy adult under 50, the realistic worst case is usually an unpleasant week. That is not a reason to ignore it — it is a reason for households with an older or immunocompromised member to take evening bite prevention seriously during the season.
How to reduce your risk
- Treat dusk as the priority window. Apply repellent to exposed skin before evening walks, garden dinners, river or lakeside evenings and night fishing, and reapply as the label directs.
- Cover up after sunset. Long sleeves, long trousers and closed shoes remove most of the target area at exactly the time Culex feeds.
- Screen the bedroom. Intact window screens, or a net, matter more overnight than any gadget. Mosquitoes that get indoors at dusk bite through the night.
- Empty standing water weekly. Water butts, buckets, blocked gutters, plant saucers, unused paddling pools and clogged drains are where the next generation is developing.
- Keep ponds moving or stocked. Fish and moving water suppress mosquito larvae; neglected, still, nutrient-rich water encourages them.
- Watch dead birds as a signal, not a threat. Unusual numbers of dead birds, especially corvids, can indicate local virus activity. Do not handle them; report them if your country runs a surveillance scheme.
How incognito® helps
Because there is no human vaccine and no specific treatment, not being bitten is the entire prevention plan — and for West Nile virus that means a repellent you are actually willing to put on before an evening outdoors, night after night, through the summer.
Our repellents are built around PMD (Citrepel®), a plant-derived active obtained from Java citronella (Cymbopogon winterianus). PMD is the same class of skin-applied active that the EPA and CDC list alongside DEET for protection against mosquitoes; ours is clinically proven, DEET-free, vegan and biodegradable, which matters if you are applying it every evening beside a river or a lake. The DEET-free insect repellent spray is the straightforward choice for garden and evening use, and the Elite Traveller Bundle covers a longer trip through southern Europe. Whichever you use, follow the directions and reapplication guidance printed on the label of the product you own.
If you feel ill
See a doctor promptly if you develop a high fever with a severe headache, a stiff neck, confusion, unusual drowsiness, tremors or muscle weakness during or shortly after the mosquito season — and mention where you have been. A mild summer fever after a few bites is very unlikely to be West Nile virus, but neurological symptoms always warrant urgent assessment, particularly in older adults.
FAQs
Is West Nile virus dangerous?
For most people, no. About 80% of infections cause no symptoms and around 20% cause a flu-like illness that resolves on its own. Fewer than 1% develop serious neurological disease, and that risk is concentrated in people over 60 and those who are immunocompromised.
Which countries in Europe have West Nile virus?
Locally acquired cases are reported most summers from Italy, Greece, Romania, Hungary, Bulgaria, Serbia, Spain, France, Austria and Croatia, among others. The affected regions shift each year, so check the ECDC weekly updates during the season.
Is there a vaccine for West Nile virus?
There is a vaccine for horses, but none licensed for humans. There is also no specific antiviral treatment, which is why avoiding mosquito bites is the only real protection.
What time of day do West Nile mosquitoes bite?
Mainly from dusk through the night and into the early morning. That is different from the day-biting tiger mosquito that spreads dengue, so evening protection is the priority for West Nile virus.
Can West Nile virus be passed from person to person?
Not through everyday contact. It spreads through mosquito bites. Rare exceptions are blood transfusion, organ transplantation and transmission from mother to baby during pregnancy or breastfeeding.
How long after a bite would symptoms appear?
Typically between 2 and 14 days. Anyone with a high fever plus a severe headache, stiff neck or confusion in that window should seek medical attention promptly.
Sources
- ECDC — West Nile virus infection
- ECDC — Facts about West Nile virus infection
- WHO — West Nile virus fact sheet
- CDC — About West Nile virus
- ECDC — Protective measures against mosquitoes
- CDC — Preventing mosquito bites
- US EPA — Skin-Applied Repellent Ingredients
This article is general information, not medical advice. If you develop a fever, severe headache, stiff neck, confusion or muscle weakness during or after the mosquito season, seek medical attention promptly. Always read and follow the label of any repellent you use.
Written by the incognito® team.