West Nile virus is endemic in Berlin. A Charite research team has shown the virus overwinters and circulates locally in the city's Culex mosquitoes, and Germany logged four locally acquired human West Nile cases in 2025. This is a night-biting Culex risk answered by a net over the bed and a screen on the window, and it is a separate problem from the day-biting tiger mosquito headlines out of Bonn, Koln and the wider Rhineland.
West Nile virus is now endemic in Berlin. That is the plain finding: the virus overwinters in the city and circulates locally each summer in resident Culex mosquitoes, so a person can be infected in Berlin without leaving Germany [Charite 2026]. Germany recorded four locally acquired human West Nile cases in 2025, and the household protection answer is a night-time one: a net over the bed and a screen on the window [RKI 2026].
This piece does two things. It reports what the German figures actually say, source by source, without rounding away the parts that complicate the headline. And it separates two mosquito stories that the July press keeps merging: the day-biting tiger mosquito spreading through the Rhineland, and the night-biting Culex that carries West Nile in the east. They are different insects, on different timetables, asking for different protection.
The headline finding: established, not visiting
For years the working assumption was that West Nile virus arrived in Germany with migrating birds each summer and faded out each winter. A Charite research team has now shown that this is no longer true for Berlin. The virus is established: it persists locally between seasons and re-emerges from the city's own mosquito population rather than being re-imported [Charite 2026]. The peer-reviewed basis sits in Eurosurveillance, which documented ecological and clinical evidence of establishment in the Berlin urban area across 2021 to 2022 [Eurosurveillance 2023].
The fieldwork is concrete. The Charite team trapped roughly 24,000 mosquitoes and tested how many carried the virus. In Berlin-Schoneberg, between 0.6 and 6 percent of the mosquitoes caught in summer 2023 carried West Nile virus, and between 0.2 and 2 percent in 2024 [Charite 2026]. Those are small percentages, but a small infection rate in a common urban mosquito, sustained across seasons, is the definition of endemic circulation rather than a one-off spillover.
The virus did not appear from nowhere. West Nile virus was first detected in German birds and horses in 2018, and the first human infection acquired inside Germany was reported in 2019 [RKI 2026]. The early years were confined to Central-East Germany. A peer-reviewed 2022 to 2024 update, with data current to 1 July 2025, describes a slow annual spread that intensified in 2024 and produced numerous infections in the northwest of the country, mostly in animals [Karger 2025]. Establishment in Berlin is the human-facing edge of that longer trend.
What Germany's numbers say, exactly
Numbers on West Nile virus are easy to misquote because there are several different counts and they measure different things. Here is the clean version.
- Locally acquired (autochthonous) cases: the RKI reports between 4 and 35 locally acquired infections each year since 2019 [RKI 2026]. The peak was 2024, when Germany confirmed 49 infections nationwide and 35 of them were acquired inside the country [Karger 2025]. The 2025 season was mild, with 4 locally acquired cases [RKI 2026].
- 2026 so far: one locally acquired case, as of 29 July 2026 [RKI 2026].
- Where they occur: the infections have so far occurred mainly in eastern Germany, in Berlin, Brandenburg, Saxony-Anhalt, Saxony and Thuringia; in 2024 individual cases were also recorded in Schleswig-Holstein, Lower Saxony and North Rhine-Westphalia [RKI 2026].
- Deaths: none of the West Nile infections reported in Germany from 2022 to 2024 was fatal [Karger 2025].
So when a headline reports the German numbers, the honest reading is: a small number of locally acquired infections each year, concentrated in the east, plus travel-associated cases picked up abroad [RKI 2026] [Karger 2025]. The establishment finding does not rest on the case count being large. It rests on the virus being present in local mosquitoes every year.
The counted cases are also only the visible layer. Most West Nile infections cause no symptoms at all, so they are never tested or reported. The RKI's own breakdown is that about 20 percent of infected people develop a feverish, flu-like illness, and only about 1 in 100 becomes severely ill with neuroinvasive disease [RKI 2026]. On that basis the Charite virologist Victor Corman has estimated that the true number of people who have had West Nile fever in Berlin could be at least a hundred times higher than the reported figure [Charite 2026]. A low official count in a disease that is mostly silent is a measurement artefact, not reassurance.
For scale, the European picture in 2025 was much larger: as of early December, 14 European countries reported 1,112 locally acquired human West Nile cases to ECDC surveillance [ECDC 2025]. Germany sits at the cool northern edge of that map, which is exactly why local establishment in a northern capital is the notable development.
Why this is not the tiger mosquito story
July 2026 produced two overlapping German mosquito narratives, and merging them leads households to the wrong protection. They are separate.
No. The RKI states that Culex mosquitoes, which are widespread in Germany, are the main vectors of West Nile virus [RKI 2026]. The ECDC's factsheet adds that Aedes albopictus, the Asian tiger mosquito, is a competent vector in the laboratory but of little importance for transmission [ECDC 2026]. These are different species with different behaviour:
- Different vector. West Nile virus is a Culex problem. The tiger mosquito is the vector of concern for dengue, chikungunya and Zika, which is a different set of diseases [WHO 2026].
- Different geography. West Nile circulation is concentrated in eastern Germany, above all in Berlin, Brandenburg, Saxony-Anhalt, Saxony and Thuringia [RKI 2026]. The tiger mosquito, by contrast, has been recorded along motorways and has reproduced locally in southern Germany since 2014 [ECDC 2026].
- Different clock. The tiger mosquito bites during the day, outdoors, around ankles on a terrace or in a garden. ECDC states that Culex mosquitoes mainly bite between dusk and dawn, both indoors and outdoors, and that bed nets and screened rooms are the personal protection for the evening and night [ECDC 2026]. This is the single most important practical distinction, because it decides where and when you need protection.
The consequence is simple. Daytime tiger-mosquito exposure is a terrace and garden question. Night-time West Nile exposure is a bedroom question. A household in Berlin is mostly facing the second one.
The vector behind West Nile: Culex pipiens and the night window
The species doing the work is Culex pipiens, small, brown and unremarkable, plus its urban sibling form that breeds in cellars and standing water in buildings. Three of its habits set the protection logic:
- It feeds at night. Biting peaks in the hours after sunset and before sunrise. An open, unscreened bedroom window on a warm August night in Berlin is the exposure that matters [ECDC 2026].
- It breeds in larger standing water. Not the bottle-cap puddles the tiger mosquito uses, but blocked gutters, water butts, neglected ponds, flooded cellars and any organically rich standing water. Source reduction works, but it targets different water [RKI 2026].
- It comes indoors. Unlike the tiger mosquito, Culex pipiens readily enters homes to feed. Indoor biting is the rule for West Nile-relevant transmission, which is why the last barrier is the one at the bed [ECDC 2026].
There is no West Nile vaccine for people; the WHO notes that vaccines are available for horses, as a separate veterinary programme [WHO 2026] [ECDC 2026]. For people, the protective layer sits in the home, not the clinic.
The protection answer: physical, at the window and the bed
Because the vector is nocturnal and enters bedrooms, the reliable protection is structural. The RKI's own public guidance lists mosquito nets and window screens alongside covering clothing and repellents as the measures that reduce bites, and singles out people at higher risk of severe illness as those who should protect themselves [RKI 2026].
A practical, chemical-free protocol for a Berlin household through the West Nile season:
- Screen the windows you sleep with open. A fitted insect screen lets you ventilate on a hot night without opening the room to Culex. This is the highest-value single step, because it addresses the exact behaviour, indoor night biting, that drives risk.
- Put an untreated net over the bed. A fine-mesh physical barrier over the sleeping area stops the mosquito reaching skin during the dusk-to-dawn feeding window, with no insecticide involved. An untreated net is not a biocidal product and carries no chemical claim under the EU Biocidal Products Regulation [EU 2012]; it works by mechanical exclusion alone.
- Reduce standing water around the building. Clear blocked gutters, empty water butts or screen them, and drain neglected containers and saucers. This shrinks the local Culex population that the bed net and screen then keep off you.
- Add repellents as a supplement, not a substitute. Where skin is exposed outdoors at dusk, an approved repellent is a reasonable top-up, but it is a supplement to the physical barrier, not a replacement for it.
The logic is deliberately narrow. West Nile virus asks one household question, can a Culex mosquito reach a sleeping person between dusk and dawn, and the answer is a net, a screen and drained water, not a pharmacy shelf.
What to watch through the rest of 2026
Establishment means the baseline has shifted, not that a large outbreak is due. The things that will actually move the German picture are the RKI's autochthonous case notifications through late summer and early autumn, the Berlin city figures specifically, and whether the northward and westward spread seen in animals in 2024 turns into more human cases outside the east [RKI 2026] [Karger 2025]. ECDC records that most human West Nile infections in Europe are observed between July and September; the RKI says the German season peaks in late summer and, in sustained warm weather, runs into early autumn [ECDC 2026] [RKI 2026]. The season is not a July event.
For a household, none of that changes the action. The virus is present in Berlin's mosquitoes now, the exposure is at night indoors, and the protection is the barrier at the window and the bed.
Last updated 2026-07-31.
This article is general information, not medical advice. Ask a doctor or pharmacist about your own health.