Mosquitoes have found ideal conditions for the wide transmission of West Nile virus this summer, with significantly more cases than in the past seven years. Attica is at the epicentre of the outbreak, and by the middle of last week at least 31 municipalities had recorded cases, with a further seven at high risk. The increased rainfall of previous months, combined with a particularly mild winter, created the conditions for the virus’s resurgence, raising concerns about how the situation will develop over the summer.

According to the most recent official figures from Greece’s National Public Health Organisation (EODY), 157 cases of West Nile virus infection had been diagnosed and reported in the country by the morning of Wednesday, 19 August. Among those infected is journalist Antonis Panoutsos, who was admitted to intensive care. Of the total cases, 116 presented with Central Nervous System complications (encephalitis and/or meningitis and/or acute flaccid paralysis), while 41 had mild CNS symptoms or none at all. In total, 13 patient deaths had been recorded by 19 August, with a median age of 82. The scale of this year’s West Nile virus challenge becomes clear when compared with last year’s figures. The whole of 2025 saw 96 cases and nine deaths. According to experts, Greece has not seen an outbreak of this scale since 2018.

“We had a very warm winter, along with humidity and heavy rain, with standing water favouring mosquito breeding,” Theodoros Vasilakopoulos, chair of EODY’s Scientific Council, tells Proto Thema, pointing to one of the reasons behind the virus’s resurgence. “A second factor is how much immunity the birds that transmit the virus to mosquitoes have. These are wild birds that migrate from Africa, and depending on the year they may have more or less immunity. It’s partly down to luck,” he adds.

Citing the European Centre for Disease Prevention and Control (ECDC), Theodora Psaltopoulou, professor of therapeutics, epidemiology and preventive medicine at the National and Kapodistrian University of Athens (NKUA), stresses that West Nile virus is circulating in nine European countries, including Balkan states, mainly Italy, but also Spain, France and Germany. “West Nile virus has also been the subject of leading international scientific journals, which have published several related articles in recent months. The overall message is that the virus is now regarded as a growing, geographically expanding threat in Europe, with climate and the urban environment playing a significant role,” she says.

The precise reasons why 2026 has become a peak year for West Nile virus remain a matter of speculation, since the virus is unpredictable, argues Antonis Michailakis, a researcher at the Benaki Phytopathological Institute. “One key factor affecting the mosquito’s bio-ecology is, on the one hand, mild winters and, on the other, increased rainfall during spring and summer, which created ideal conditions for mosquito activity. In addition, the lack of data on the natural hosts, namely birds, makes it difficult to fully understand its spread,” he tells Proto Thema.

The virus’s transmission cycle

The common mosquito Culex pipiens becomes infected when it bites a bird carrying the virus. If the now-infected mosquito then bites another bird or mammal (mainly humans and horses fall into this category), it will pass the virus on. Mosquitoes do not become ill from the virus, and usually need 10 to 14 days after infection for the virus to multiply in their system before they can transmit it to their next victim. It is worth noting that the virus is not transmitted from person to person. However, people should take protective measures to reduce their chances of being bitten by an infected mosquito.

“Climate change is having a decisive effect on this system. Research data now shows the common mosquito present all year round, as increasingly mild winters no longer allow its population to be naturally kept in check. Sampling shows that the insect is adapting more quickly and can remain active and test positive for the virus even during the winter months, a period once thought unable to sustain the virus. At the same time, climate change may also be affecting birds’ migratory patterns. So a multifactorial system is likely taking shape, in which climate change is not simply increasing the number of mosquitoes but redefining the duration, geography and dynamics of transmission, making the virus less seasonal and more permanently present in the environment,” explains Michailakis, adding that entomological research carried out by the Benaki Phytopathological Institute over the past six years in the Attica Region, which has kept scientists occupied this year, has not recorded any increase in the population of mosquitoes that transmit the virus.

As Vasilakopoulos explains, of every 100 people who contract West Nile virus, 80% will show no symptoms at all, 19% will develop a mild fever, which is why this group is rarely identified and recorded. Only a very small proportion, 1%, will develop Central Nervous System symptoms, see a doctor and eventually be tested at specialist reference centres. “The high number of cases our country appears to have compared with other European countries is because we have the best surveillance. Other countries do not have active surveillance and do not record all serious cases, which is why it looks as though they have none,” notes the EODY Scientific Council chair.

How the spraying should be carried out

One reasonable question is whether the virus is surging because of inadequate prevention measures, namely spraying. Responsibility for spraying and controlling mosquito populations lies with Greece’s regions and municipalities. Over the past three years, since the 2023 Storm Daniel floods in Thessaly, EODY has drawn up a national plan setting out preventive measures, which regions and municipalities are then obliged to implement. There is, of course, the familiar confusion over responsibilities between regions and municipalities, such as who is responsible for a particular drain or stream.

“Although the Ministry of Health’s annual circular urges municipalities to maintain an active control programme all year round, cases are still recorded in which, once a public health problem emerges, municipalities end up relying solely on the region’s initiatives. This shows that a lack of cooperation at local level can be a significant gap in local interventions,” says Michailakis.

According to Georgios Lambrou, president of Greece’s Pest and Rodent Control Companies’ Association (SEAME), tackling mosquitoes does not rely on a fixed number of sprayings. Instead, integrated mosquito management programmes are applied, involving mapping of breeding sites, systematic entomological surveillance, limiting or eliminating breeding grounds, larviciding and, where necessary and under specific conditions, interventions against adult mosquitoes.

“The basic strategy is larviciding, meaning tackling mosquitoes before they reach adulthood. Mapped breeding sites must be checked regularly, from early spring at the latest, and treatment must begin as soon as the first larvae appear. Work continues throughout the mosquitoes’ development period and, in any case, at least until early November,” Lambrou tells Proto Thema, stressing that the timely, uninterrupted implementation of these programmes is particularly important. “The recording of a West Nile virus case should not be the starting point for mosquito management. Prevention needs to have already taken place,” he says, adding: “Regions and municipalities have distinct but complementary roles. Against this backdrop, we are particularly concerned that there have been cases of areas where, at the time a human case was recorded, no standalone mosquito management programme was under way at municipal level.”

What citizens should do

A key pillar of the strategy to prevent West Nile virus is personal protective measures. Experts recommend using approved body and environmental insect repellents. Citizens are also urged to use window screens, mosquito nets, air conditioning and fans, and to wear clothing that covers the skin.

Draining standing water from yards, gardens, verandas, roof terraces, balconies, fields and plots of land is also very important. Care should be taken with anything that collects water, such as plant pot saucers, which should be turned upside down or covered.

What can someone do at home if they have a serious problem with mosquito bites? “The first and most important step is to identify and limit breeding sites. Even small amounts of standing water in plant pot saucers, buckets, containers, gutters, drains, tanks or other objects can act as mosquito breeding grounds,” notes Lambrou, adding: “If the problem is severe or persists, people should contact a legally operating professional pest and rodent control company that has made the required notification to the Ministry of Rural Development and Food.

The scientist in charge must first inspect the property and assess where the problem is coming from. Possible breeding sites must be sought out, the mosquito species causing the nuisance identified, and the site’s environmental conditions examined. Only after the inspection can a decision be made on whether a biocide application is needed and which method is suitable.”

Symptoms

Mild illness: The mild form can present with symptoms such as fever, headache, general weakness or fatigue, and muscle and joint pain (resembling flu), while gastrointestinal symptoms (nausea, vomiting, diarrhoea, loss of appetite, abdominal pain), skin rashes and swollen lymph nodes can also occur.

Severe form of the disease: Fewer than 1 in 100 people who become infected (mainly older adults) develop the severe form of the disease, which affects the Central Nervous System (encephalitis, meningitis or acute flaccid paralysis). Symptoms of the severe form can include fever, headache, neck stiffness, changes in level of consciousness and behaviour (apathy, lethargy, disorientation, confusion, coma), neurological symptoms (unsteadiness, gait and mobility problems, tremor, seizures, paralysis), severe muscle weakness and visual disturbances.