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Chikungunya is transmitted to humans by mosquitos infected with the chikungunya virus (CHIKV). Globally, the disease affects more than 1 million people every year. In Europe, chikungunya is mostly spread by travellers. The disease has similar symptoms (fever and joint pains) as some other viral diseases with an overlapping geographical distribution, such as dengue. Therefore, many patients are misdiagnosed, and the socio-economic impact and total disease burden is probably underestimated (Kam et al., 2015).

Chikungunya 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, 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 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 on the map and is labelled as 'unreported' (last updated in April 2023).

Source & transmission

The CHIKV is primarily transmitted between humans via Aedes mosquitos. These mosquitos bite in daylight, with peaks of activity in the early morning and late afternoon. An uninfected mosquito can become infected with the virus when it feeds on an infected person or animal. After a short period of replication of the virus, the infected mosquito can then transmit the virus to uninfected humans with a bite (Tsetsarkin et al., 2016), and remains infectious for the rest of its life (Mbaika et al., 2016). Compared to other mosquito-borne viruses, the CHIKV can move to a new host more quickly with the complete transmission cycle – from human to mosquito and back to another human – occurring in less than a week. In Europe, local transmission was first reported in 2007 in North-Eastern Italy. Most cases occurring in Europe (>90%) are related to travel.

Of the Aedes mosquito species present in Europe, Ae. albopictus – the Asian tiger mosquito – is responsible for most of the CHIKV transmissions and the largest disease outbreaks. Ae. albopictus was first detected in Europe in 1979 and is now present in 28 European countries (ECDC, 2021b). The species thrives in a wider geographical range than Ae. Aegypti – the Yellow fever mosquito – which is also an efficient vector but still rather rare in Europe and neighbouring areas. Nevertheless, 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).

Health effects

Chikungunya can manifest itself as an acute illness, from which patients can recover rapidly (in less than two weeks) or which can progress to a chronic disease that lasts weeks to years. Usually, patients start feeling sick 4-8 days after a mosquito bite. The disease causes a sudden high fever, frequently paired with aching joints, requiring bed rest. In addition, patients may suffer from swollen ankles and wrists, painful muscles, headaches, rashes, nausea or fatigue (WHO, 2022). Most infected individuals suffer only mildly and about 15% show no symptoms at all. In these cases, full recovery is common and immunity against the CHIKV is thought to be life-long. Yet, when the disease is serious, patients can be hospitalized due to severe skin rashes, neurological infections, heart muscle inflammations, liver infections or even multi-organ failure. Such serious complications are rather uncommon, but for infants or the elderly chikungunya can be life threatening (Burt et al., 2017).

Morbidity

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

  • 3,671 cases, of which >90% are imported cases (ECDC, 2023)
  • The EU/EEA notification rate was below 1 cases per 100 000 population in 2020
  • Rarely ending fatal: no chikungunya related deaths recorded yet in Europe
  • The number of cases has been varying yearly in the period 2015-2019 between 111 in 2018 and 534 in 2015, without an obvious trend. In 2020 and 2021, only 59 and 13 cases were reported. These low numbers are probably related to Covid-19 measures and underreporting.
  • Local transmission of chikungunya is rare in Europe, but locally acquired cases have been reported in France and Italy in 2017 (17 and 277 cases respectively), in France in 2014 (11 cases) and 2010, and in Italy in 2007.

(ECDC, 2014-2022)

Distribution across population

  • Age group with the highest disease rate in Europe: 25 – 64 years old (ECDC, 2014-2022)
  • Groups at risk of severe disease course: infants, elderly, people with a pre-existing health condition
  • Groups at higher risk of infection: migrant workers and travellers

Climate sensitivity

Climatic Suitability

The Ae. albopictus mosquito, the most important vector of the CHIKV, 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 as well as to extended drought periods. Mild winters with minimal temperatures of -5 °C enable establishment of a stable mosquito population (Waldock et al., 2013), as do heavy rainfalls and flooding early in summer that establish mosquito breeding sites (Tran et al., 2013). The optimum average temperature for CHIKV transmission is 27 °C, at which the viral load in the saliva of Ae. albopictus is the highest (Alto et al., 2018). Yet these mosquitos are able to transmit the CHIKV even at 20 °C, which confirms the climatic suitability of Europe’s climate for this CHIKV vector (Mercier et al., 2022). Ae. aegypti – a less important mosquito species with the potential to transmit chikungunya in Europe – has a narrower temperature tolerance and does not survive temperatures below 4 °C (Brady et al., 2013). On the other hand, this species and the viral load in its saliva is relatively insensitive to diurnal temperature variations (Alto et al., 2018).

Seasonality

In Europe, there is no clear seasonal trend in the number of chikungunya cases. In some years, the cases . reflect an increased transmission of the virus in the probable countries of infection due to climatic conditions favourable to vector activity and viral replication during that specific period of the year. To a lesser extent, also the variation in the number of retuning travellers contributes to the seasonality among travel-related cases (ECDC, 2014-2022).

Climate Change Impact

Climatic changes in Europe, including higher mean temperatures, humidity and precipitation intensity, lead to a better climatic suitability for Ae. albopictus, hence higher risks for chikungunya infections in most parts of Europe (Jourdain et al., 2020; Mercier et al., 2022). Climatic suitability for transmission of chikungunya within Europe has already increased in recent decades and in the future both the suitability index for the tiger mosquito and the length of its active season are expected to further rise in several countries. Higher temperatures lead to more favourable conditions for mosquito reproduction, increased egg hatching rate and faster development of Ae. albopictus larvae, as well as longer active seasons for mosquitos. This causes larger mosquito populations and more mosquito bites. Moreover, higher average summer temperatures promote virus replication in the mosquito. Higher humidity is expected to elongate the life span of the mosquitos (Marini et al., 2020). A study of the Rhine and Rhone rivers surroundings identified these environments as hot spots for mosquito activity and disease outbreaks within Europe (Tjaden et al., 2017). Across Central Europe, particularly in France and Italy, Ae. albopictus mosquito populations are expected to establish. Stable Ae. albopictus populations were already found at altitudes above 900 m above sea level in central Italy where temperatures in winter drop to -5 °C. The mosquitos are expected to spread to even higher regions in the future (Romiti et al., 2022) and northwards (Peach et al., 2019). Still, in other countries that currently have suitable conditions for mosquito populations, such as Northern Italy, the expected rise in summer droughts decreases the habitat suitability for the tiger mosquito (Tjaden et al., 2017).

On Europe’s mainland, also an expansion of the Ae. aegypti mosquito population is expected. This species has a narrower preferred temperature range and will mainly benefit from the temperature rise that makes Europe’s climate more suitable for its survival (Medlock and Leach, 2015).

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 breeding opportunities in open natural and artificial waters, and 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 environment (e.g. see the case studies of the ‘Mückenatlas’ initiative or the EYWA project)
  • Vaccines are in clinical trial phases but not yet ready to use

Treatment

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

References

Alto, B. W. et al., 2018, Diurnal Temperature Range and Chikungunya Virus Infection in Invasive Mosquito Vectors, Journal of Medical Entomology 55(1), 217–224. https://doi.org/10.1093/jme/tjx182

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), 1-11. https://doi.org/10.1186/1756-3305-6-351

Burt, F. J. et al., 2017, Chikungunya virus: An update on the biology and pathogenesis of this emerging pathogen, The Lancet Infectious Diseases 17(4), e107–e117. https://doi.org/10.1016/S1473-3099(16)30385-1

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 – Chikungunya virus disease. Available at https://www.ecdc.europa.eu/en/all-topics-z/chikungunya-virus-disease/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.

Jourdain, F. et al., 2020, From importation to autochthonous transmission: Drivers of chikungunya and dengue emergence in a temperate area, PLOS Neglected Tropical Diseases 14(5), e0008320. https://doi.org/10.1371/journal.pntd.0008320

Kam, Y.-W. et al., 2015, Sero-Prevalence and Cross-Reactivity of Chikungunya Virus Specific Anti-E2EP3 Antibodies in Arbovirus-Infected Patients, PLoS Neglected Tropical Diseases 9(1), e3445. https://doi.org/10.1371/journal.pntd.0003445

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 

Mbaika, S. et al., 2016, Vector competence of Aedes aegypti in transmitting Chikungunya virus: Effects and implications of extrinsic incubation temperature on dissemination and infection rates, Virology Journal 13(114), 1–9. https://doi.org/10.1186/s12985-016-0566-7

Medlock, J. M. and Leach, S. A., 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), 1-11. 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

Peach, D. A. et al., 2019, Modeled distributions of Aedes japonicus japonicus and Aedes togoi (Diptera: Culicidae) in the United States, Canada, and northern Latin America, Journal of Vector Ecology 44(1), 119-129. https://doi.org/10.1111/jvec.12336

Romiti, F. et al., 2022, Aedes albopictus abundance and phenology along an altitudinal gradient in Lazio region (central Italy), Parasites Vectors 15(92), 1-11. https://doi.org/10.1186/s13071-022-05215-9

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

Tran, A. et al., 2013, A Rainfall- and Temperature-Driven Abundance Model for Aedes albopictus Populations, International Journal of Environmental Research and Public Health 10(5), 1698–1719. https://doi.org/10.3390/ijerph10051698

Tsetsarkin, K. A. et al., 2016, Interspecies transmission and chikungunya virus emergence, Current Opinion in Virology 16, 143–150. https://doi.org/10.1016/j.coviro.2016.02.007

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 (2022). World Health Organization, https://www.who.int/. Last accessed August 2022.

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