Looking at data from a large dengue outbreak in Italy in 2024, researchers examined the main transmission hotspots and the influence of factors such as temperature and mosquito control measures to identify dengue transmission patterns in Europe.

Dengue is caused by the dengue virus and transmitted by mosquito bites. Traditionally endemic in tropical regions such as Latin America and the Caribbean as well as South-eastern Asia, local transmission across several countries in mainland Europe has been documented since 2010. Particularly the mosquito species Aedes albopictus, which is now well-established in southern Europe, can act as a dengue vector even though the main dengue vector is Aedes aegypti.

In their article published in Eurosurveillance, Grané et al. analysed data from a dengue outbreak across three municipalities in Italy between July and October 2024. The outbreak resulted in 296 probable and confirmed locally acquired infections with dengue virus serotype 2, of which 286 occurred among residents in the municipalities Fano, Cavezzo and Ortona. Even though the extensive investigations could not identify the primary case that initiated local transmission, the study found that 270 of the reported cases were probably exposed near someone who was already infected.

Transmission Influenced by Spatial Proximity

Based on their data analysis, the researchers found that transmission during this dengue outbreak was largely localised: more than half of linked transmission events involved people whose probable exposure sites were located less than 100 metres apart. Among people for whom a likely source of infection could be identified, 18% were linked to transmission within the same household and 41% to transmission in the immediate neighbourhood.

The data imply that the likelihood of transmission went down with increasing distance, as 27% of transmission events were associated with exposure sites located between 100 and 200 metres apart while only 10% happened between 200 and 300 metres apart. Transmission beyond 400 metres was rare, accounting for less than 1% of identified links. According to the authors, these findings are consistent with the limited flight range of Aedes albopictus mosquitoes.

Impact of Control Measures and Temperatures

Before the outbreak was detected, each person with dengue symptoms infected, on average, more than one other person. Following outbreak detection and the implementation of mosquito control measures within a 200-metre radius around identified exposure sites, this average fell to below one secondary infection per infected person, indicating a decline in transmission. In addition, the data analysis showed that a drop in temperatures during the autumn of 2024 likely contributed to reducing transmission. In turn, the authors estimate that each 1°C increase in temperature was associated with an approximate 20% rise in transmission.

The authors conclude that “the high proportion of focal transmission suggests that, when cases are diagnosed promptly, vector control and active case finding within a buffer of ca 400 m around detected cases may substantially reduce onward transmission.” They note that “when delays in case detection occur, extending mosquito control to nearby surrounding areas or at the municipality level might be advisable to cope with the undetected transmission spread.”

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Journal: Eurosurveillance
DOI: 10.2807/1560-7917.ES.2026.31.27.2600035
Article Title: Autochthonous transmission patterns of dengue virus serotype 2 in Italy: evidence from outbreaks in 2024
Publication Date: 9-Jul-2026