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Dengue

Dengue is a mosquito-borne viral disease, causing at least 390 million infections per year and putting a thousand times higher number of people at risk of contracting an infection (WHO, 2012). The estimated global incidence of dengue has grown 30 times over the past 50 years (Li and Wu, 2015) due to a variety of factors, including globalization, travel, trade, socio-economic factors, human settlement, viral evolution, and possibly climate change (Murray et al., 2013). Travelers often transport the dengue virus (DENV) between countries (WHO, 2022) and in Europe most cases (>99%) are travel related. The climatic suitability for transmission of dengue within Europe is already increasing, and expected higher temperatures in the future will create even more favorable conditions for the dengue carrying mosquitos in several parts of central Europe.

Dengue notification rate (map) and reported cases (graph) in Europe

 

Source: ECDC, 2023, Surveillance Atlas of Infectious Diseases

Notes:

Map and graph show data for the EEA member countries, excluding Bulgaria, Cyprus, Denmark, Iceland, Liechtenstein, Norway, Switzerland and Türkiye due to absence of data. The boundaries and names shown on this map do not imply official endorsement or acceptance by the European Union.

The disease is notifiable at the EU level, but the reporting period varies among the countries.

When countries report zero cases, the notification rate on the map is shown as '0'. When countries have not reported on the disease in a particular year, the rate is not visible in the map and is labelled as 'unreported' (last updated in April 2023).

 

Source & transmission

The DENV is mainly transmitted to humans via infected female Aedes mosquitos. These mosquitos bite in daylight, though there may be peaks of activity in the early morning and late afternoon. A mosquito becomes infectious when it feeds on a person with DENV. The infected mosquito remains infectious and hazardous for other people for the rest of its life (WHO, 2022). Dengue can also be transmitted from a pregnant mother to her infant (Sinhabahu et al., 2014). Transmission via blood during organ donation or blood transfusions is rare (Pozzetto et al., 2015).

The Aedes aegypti mosquito is the primary vector of the DENV in the world. It is well adapted to the warm and humid climate of the (sub-)tropics. Ae. aegypti used to be present in Europe, and particularly in the Mediterranean basin, up to the middle of the 20th century, after which the species became rare following changing hygienic circumstances. Recently however, Ae. aegypti was observed more regularly again in certain parts of Europe (Trájer, 2021). It is established in Madeira (Portugal), Southern Russia, and Georgia, and has been introduced in Türkiye, the Canary Islands (Spain) and Cyprus (ECDC, 2021a; Miranda et al., 2022). 

Aedes albopictus is a secondary, less competent dengue vector. Yet this mosquito species, due to its tolerance of lower temperatures, is more relevant in Europe, where it is present in 28 European countries and at altitudes up to 1200 m above seas level (ECDC, 2021b). Ae. albopictus caused in 2010 the first local transmissions of dengue in Europe (in France and Croatia), and several European outbreaks thereafter, especially in Italy and France. Outbreaks usually are tracked back to infected travellers from tropical countries (Mercier et al., 2022).

Four different serotypes (i.e., subtypes) of the DENV are known. Patients recovering from an infection with one type are mostly immune against that type for the rest of their life but are not immune against other types (Murugesan and Manoharan, 2020).

Health effects

Dengue causes a wide spectrum of symptoms. While most cases are asymptomatic or mild, dengue can also manifest as a severe, flu-like illness that may even be fatal in rare cases. In general, dengue can be recognized when a high fever (around 40°C) is accompanied by at least two more symptoms such as a severe headache, pain behind the eyes, aching muscles and joints pains, nausea, vomiting, swollen glands or a rash. Symptoms usually last for 2-7 days, after an incubation period of 4-10 days. Although less common, some people develop severe dengue, which manifests as severe abdominal pains, persistent vomiting, rapid breathing, bleeding gums or nose, fatigue, restlessness, liver enlargement, blood in vomit or faeces. This severe form of dengue can lead to complications including serious bleeding, organ impairment or even plasma leakage (Umakanth and Suganthan, 2020; WHO, 2022). Dengue fever during pregnancy can result in lower birth weight, higher risk of foetal distress, and preterm birth (Sinhabahu et al., 2014).

Morbidity in Europe

In the EEA member countries (excluding Bulgaria, Cyprus, Denmark, Liechtenstein, Switzerland and Türkiye due to the absence of data), for the period 2008-2021:

  • 22,164 dengue virus infections were reported , of which around 90% was travel-related (ECDC, 2023)
  • The EU/EEA notification rate was 0.5 cases per 100 000 population in 2020 
  • No clear trend in the number of cases could be discerned since 2016, whereas the number of cases steadily increased between 2011 and 2016
  • The number of locally acquired cases increased since 2013 up to 24 cases in 2020, with most cases detected in France, Spain and Italy

(ECDC, 2014-2022)

Distribution across population

  • Age group with the highest disease rate in Europe: 25 – 44 years old, both men and women (ECDC, 2014-2022)
  • Groups at risk of severe disease course: infants, elderly, people with weak immunity
  • Groups at higher risk of infection: migrant workers and travellers

Climate sensitivity

Climatic suitability

The likelihood of DENV transmission is temperature-dependent, with the highest infection rate occurring when environmental temperature is 31 °C (Xiao et al., 2014).

DENV vectors, the Aedes mosquitos, require natural or artificial containers filled with water for reproduction, even though eggs can remain viable for several months in dry conditions and will hatch as soon as they are in contact with water (WHO, 2022). Many recent local transmissions take place in suburban residential areas, which have (semi)natural areas that provide a habitat for mosquitos and at the same time have relatively high population densities (Cochet et al., 2022). Although Ae. albopictus is a secondary, less competent dengue vector, it could play a major role in the geographic spread of the disease in Europe. Ae. albopictus can survive in a broad range of climatic conditions and was found at altitudes up to 1200 m above sea level. Its eggs are highly resistant to both high and low temperatures and extended drought periods. Mild winters with minimal temperatures of -5 °C enable establishment of a stable mosquito population (Waldock et al., 2013). Ae. aegypti has a narrower temperature tolerance than Ae. albopictus, with temperatures below 4 °C being fatal for the mosquito (Brady et al., 2013).  

Seasonality

In Europe, peaks in the number of dengue cases vary yearly. The highest numbers are often recorded in August and November, but in some years also in January and March-April. The observed peaks reflect the seasonal transmission patterns in the probable countries of infection, which are related to favourable climatic conditions, as well as the seasonality of inbound travel (ECDC, 2014-2022).

Climate change impact

Alongside the increasing number of travel-related dengue cases, the rising temperatures, humidity and precipitation intensity associated with climate change are linked to a higher number of dengue cases in Europe (Stephenson et al., 2022). Climatic suitability for transmission of dengue within Europe has already increased in recent decades. A warmer climate (with temperatures up to 31 °C) leads to faster virus replication and higher virus loads in mosquitos, hence a higher infection risk to people (Xiao et al., 2014). Higher temperatures also create more favourable conditions for mosquito reproduction and faster development of larvae, resulting in larger mosquito populations. Higher humidity may extend the life span of the mosquitos (Marini et al., 2020). Altered rainfall patterns may favour or limit mosquito reproduction and activity, depending on the timing. In certain parts of Europe, especially France and Italy, Ae. albopictus mosquito populations are expected to establish after northward migration. The climatic suitability index for the tiger mosquito and the suitable season length are projected to increase in the future in several regions in Europe. Still, in some countries that currently have suitable conditions for mosquito populations, such as Northern Italy, the expected rise in summer droughts will decrease habitat suitability for the tiger mosquito (Tjaden et al., 2017). An expansion of the Ae. aegypti mosquito population is expected in Europe. This species has a narrower preferred temperature range and will mainly benefit from the rise in temperature that makes Europe’s climate more suitable for its survival (Medlock and Leach, 2015; Yadav et al., 2004).

 

Prevention & Treatment

Prevention

  • Personal protection: long-sleeved clothes, mosquito repellents, nets or screens, and avoidance of mosquito habitats
  • Mosquito control: environmental management, e.g., minimizing reproduction opportunities in open natural and artificial waters, biological or chemical measures (e.g. see the activities of the mosquito control action group in Germany)
  • Awareness raising about disease symptoms, disease transmission and mosquito bite risks
  • Active monitoring and surveillance of mosquitos, disease cases and the environment to prevent transmission (see e.g. the case studies of the ‘Mückenatlas’ initiative, dengue surveillance in France or the EYWA project)
  • The currently existing dengue vaccine is only for persons aged 9 to 45 years old in endemic areas with an infection in the past. Other dengue vaccine candidates are under evaluation but not yet ready to use (Chawla et al., 2014; WHO, 2022).

Treatment

  • No specific and effective antiviral therapy
  • Rehydration and bed rest
  • Medical advice to prevent complications
  • For severe cases: pain medication, fever-reducing drugs or treatments for arthritis

 

Links to further information

 

References

Brady, O. J. et al., 2013, Modelling adult Aedes aegypti and Aedes albopictus survival at different temperatures in laboratory and field settings, Parasites & Vectors 6(351), 1-12. https://doi.org/10.1186/1756-3305-6-351

Chawla, P. et al., 2014, Clinical implications and treatment of dengue, Asian Pacific Journal of Tropical Medicine 7(3), 169–178. https://doi.org/10.1016/S1995-7645(14)60016-X

Cochet, A., et al., 2022, Autochthonous dengue in mainland France, 2022: geographical extension and incidence increase, Eurosurveillance 27(44), 2200818. https://doi.org/10.2807/1560-7917.ES.2022.27.44.2200818

ECDC, 2021a, Aedes aegypti - current known distribution: March 2021. Available at https://www.ecdc.europa.eu/en/publications-data/aedes-aegypti-current-known-distribution-march-2021. Last accessed December 2022.

ECDC, 2021b, Aedes albopictus - current known distribution: March 2021. Available at https://www.ecdc.europa.eu/en/publications-data/aedes-albopictus-current-known-distribution-march-2021. Last accessed December 2022.

ECDC, 2014-2022, Annual epidemiological reports for 2012-2020 - Dengue fever. Available at https://www.ecdc.europa.eu/en/dengue-fever/surveillance-and-disease-data/annual-epidemiological-reports. Last accessed April 2023.

ECDC, 2023, Surveillance Atlas of Infectious Diseases. Available at https://atlas.ecdc.europa.eu/public/index.aspx. Last accessed April 2023.

Li, Y. and Wu, S., 2015, Dengue: What it is and why there is more, Science Bulletin 60(7), 661–664. https://doi.org/10.1007/s11434-015-0756-5

Marini, G. et al., 2020, Influence of Temperature on the Life-Cycle Dynamics of Aedes albopictus Population Established at Temperate Latitudes: A Laboratory Experiment, Insects 11(11), 808. https://doi.org/10.3390/insects11110808

Medlock, J. M. et al., 2015, Effect of climate change on vector-borne disease risk in the UK, The Lancet Infectious Diseases 15(6), 721–730. https://doi.org/10.1016/S1473-3099(15)70091-5

Mercier, A. et al., 2022, Impact of temperature on dengue and chikungunya transmission by the mosquito Aedes albopictus, Scientific Reports 12(6973), 1-13. https://doi.org/10.1038/s41598-022-10977-4

Miranda, M. Á., et al., 2022, AIMSurv: First pan-European harmonized surveillance of Aedes invasive mosquito species of relevance for human vector-borne diseases, Gigabyte 2022, 1–13. https://doi.org/10.46471/gigabyte.57

Murray, N. E. et al., 2013, Epidemiology of dengue: past, present and future prospects, Clinical Epidemiology 20(5), 299-309. https://doi.org/10.2147/CLEP.S34440

Murugesan, A. and Manoharan, M., 2020, Dengue Virus. In: Ennaji, M.M. (Ed), Emerging and Reemerging Viral Pathogens 1, 281–359. Elsevier. https://doi.org/10.1016/B978-0-12-819400-3.00016-8

Pozzetto, B. et al., 2015, Is transfusion-transmitted dengue fever a potential public health threat?World Journal of Virology 4(2), 113–123. https://doi.org/10.5501/wjv.v4.i2.113

Sinhabahu, V. P. et al., 2014, Perinatal transmission of dengue: A case report, BMC research notes 7(795), 1-3. https://doi.org/10.1186/1756-0500-7-795

Stephenson, C. et al., 2022, Imported Dengue Case Numbers and Local Climatic Patterns Are Associated with Dengue Virus Transmission in Florida, USA, Insects 13(2), 163. https://doi.org/10.3390/insects13020163

Tjaden, N. B. et al., 2017, Modelling the effects of global climate change on Chikungunya transmission in the 21st century, Scientific Reports 7(3813), 1-11. https://doi.org/10.1038/s41598-017-03566-3

Trájer, A. J., 2021, Aedes aegypti in the Mediterranean container ports at the time of climate change: A time bomb on the mosquito vector map of Europe, Heliyon 7(9), e07981. https://doi.org/10.1016/j.heliyon.2021.e07981

Umakanth, M. and Suganthan, N., 2020, Unusual Manifestations of Dengue Fever: A Review on Expanded Dengue Syndrome, Cureus 12(9), e10678. https://doi.org/10.7759/cureus.10678

Waldock, J. et al., 2013, The role of environmental variables on Aedes albopictus biology and chikungunya epidemiology, Pathogens and Global Health 107(5), 224–241. https://doi.org/10.1179/2047773213Y.0000000100

WHO, 2012, Global strategy for dengue prevention and control 2012–2020. World Health Organization, Geneva. Available at https://apps.who.int/iris/handle/10665/75303

WHO, 2022, World Health Organization. https://www.who.int/, last accessed August 2022

Xiao, F.-Z. et al., 2014, The effect of temperature on the extrinsic incubation period and infection rate of dengue virus serotype 2 infection in Aedes albopictus. Archives of Virology 159(11), 3053–3057. https://doi.org/10.1007/s00705-014-2051-1

Yadav, P. et al., 2004, Effect of Temperature Stress on Immature Stages and Susceptibility of Aedes Aegypti Mosquitos to Chikungunya Virus, The American Journal of Tropical Medicine and Hygiene 70(4), 346–350. https://doi.org/10.4269/ajtmh.2004.70.346