Zagreb fogs against mosquitoes over West Nile virus. Croatia is having a normal year, the Netherlands has two dead

On Tuesday, in the early morning hours, Zagreb sent vehicles spraying insecticide fog into the streets. Croatia has seven confirmed cases of West Nile virus infection, four patients are in the infectious diseases clinic, and two of them are in intensive care. Croatian experts nevertheless describe this as the usual picture for the season — and the most serious reports this week are not coming from Croatia, but from the Netherlands.

What exactly Zagreb is doing

The fogging took place from four to seven in the morning, when the fewest people are outside. The vehicles carry equipment that turns the insecticide solution into a fog of droplets smaller than 50 microns. These float in the air and then settle onto vegetation and other surfaces. Index.hr ↗

Ana Klobučarová, head of the disinfection and pest control department at the Zagreb public health institute, stresses that targeting larvae in the water is more important than treating adult mosquitoes. Larvicide measures therefore cover everything from drains in urban and suburban neighborhoods to calmer stretches of streams, garden buckets and barrels, and street storm drains. Spraying continued in Bartol Kašić Park, around Kvaternik Square, and in the neighborhoods of Savica, Bundek, Zapruđe, Utrina, Travno and Sloboština. HRT ↗

The city recommended that residents avoid staying outside during the operation and keep their windows closed. Beekeepers received a special appeal — to close their hives, since bees are extremely sensitive to insecticides. It's a detail that shows the scale of the measure: this is not spot disinfection, but a citywide intervention in the urban ecosystem.

The trigger was not only human infections. The virus was found in five dead crows at various locations around the city, and for epidemiologists that is precisely the signal that the virus is circulating locally. Zagreb residents were therefore also given instructions on what to do and who to call if they find a dead crow. N1 Croatia ↗

Why no one in Croatia is calling it an epidemic

This is worth pausing on, because the news of the spraying sounds more dramatic than the numbers behind it. Of the seven confirmed cases, two people are from Krapina-Zagorje County, where health authorities have ordered anti-epidemic measures in the surrounding area. At the same time, according to Croatian experts, seven reported infections represent the usual pattern of occurrence in the country. Index.hr ↗

The profile of the disease itself supports this. Seventy to eighty percent of those infected have no symptoms at all, and most of the rest experience something like the flu. Severe neurological complications — meningitis or encephalitis — affect fewer than one in a hundred infected people. That is precisely why the number of confirmed cases cannot be read as the number of people infected, but rather as the number of those who ended up seeing a doctor.

Croatia, then, is doing what it has practiced. Neighboring Serbia is in a similar position: between June 1 and August 30, it recorded 18 cases across seven districts, seven more than a week earlier. The average age of those infected is 63.2 years, which fits the pattern that more severe cases mainly threaten older people. The season there usually runs from June to November, and the main carrier is the Culex pipiens mosquito. Danas ↗

The unexpected number came from the north

If West Nile virus has surprised anyone this year, it is not the Balkans. On the very same day that Zagreb was spraying, Dutch authorities confirmed an infection in a 39-year-old woman from Amstelveen, near Amsterdam. What matters is that she caught the virus in the Netherlands, not while on holiday, and she developed meningitis. NOS ↗

It is the fourth confirmed case in a Dutch national this year. And unlike Croatia or Serbia, there have already been deaths there too: last month a 78-year-old man from Utrecht died from the effects of the infection, and in August a woman from the Drenthe region also succumbed to the virus. At the same time, the Dutch institute RIVM reassures that the probability of infection in the country remains very low.

The difference between south and north, then, is not in the numbers but in what they mean. Seven cases in Croatia are a repetition of a familiar pattern in a country with an established apparatus for dealing with it. Four cases and two deaths in the Netherlands, by contrast, are a more significant signal precisely because the institute there still describes the risk of infection in the country as very low.

A different mosquito, a different disease, a similar concern

Health authorities are tracking the same pattern with another disease. It is not just about the number of cases, but about where the carrier has already become established. In Cuneo, in Italy's Piedmont region, Mayor Patrizia Manasserová issued an order on Monday for emergency measures, after the local health authority reported a probable case of chikungunya virus infection. La Stampa ↗

The wording of the order itself is interesting. Chikungunya is transmitted by mosquitoes of the Aedes genus, including the tiger mosquito, which, according to the city, is "permanently present" on its territory. Not introduced, not seasonal — established. That is a condition that could create the conditions for local transmission, should the suspicion be confirmed. For now, however, Cuneo is reporting only a probable infection.

What this means for holidaymakers

Croatia is destination number one for Slovak and Czech holidaymakers, and the spraying in Zagreb sounds like a reason for concern. But the numbers don't support that — the risk is comparable to other summers, and the citywide spraying is more a sign of a functioning public health service than of failure.

What's practically useful is rather what Croatian public health officials themselves recommend, and which applies just as much at home: repellents, long sleeves and trousers during peak mosquito activity, window screens, and above all eliminating standing water. Buckets, barrels, vases, flowerpots and old tires should be emptied at least once or twice a week, since that is exactly where larvae hatch.

What hotinfo is watching

The Croatian Institute of Public Health has published its seasonal tally, and it is known whether the number of cases has exceeded the usual range.

The Dutch RIVM has issued an updated infection count, and it is clear whether the four cases have remained isolated or more have been added.

In Cuneo, Italy, the suspected chikungunya case has been confirmed or ruled out, and it is known whether local transmission occurred.

Zagreb has ended the citywide fogging, or alternatively extended it to further neighborhoods.

A locally acquired case of West Nile virus has appeared in Slovakia or the Czech Republic.