Vectorborne diseases

Climate Suitability for the transmission of Dengue - Change in the vectorial capacity for the transmission of dengue from a 1950-1959 baseline, by vector. 
_{Source: Watts, N., et al., 2021
Note: Data refer to the WHO European Region}

Health issues

Climate conditions (temperature, humidity and precipitation levels) constrain the geographical and seasonal distributions of infectious diseases, and weather affects the timing and intensity of disease outbreaks. Disease-carrying vectors of particular relevance for Europe are the Aedes albopictus mosquitoes (a vector for chikungunya, dengue and dirofilariasis), Aedes aegypti mosquitoes (a vector for chikungunya, dengue, yellow fever and zika), Culex mosquitoes (a vector for West Nile fever), Phlebotomus sandflies (a vector for leishmaniasis) and Ixodes ricinus ticks (a vector for Lyme borreliosis and tick-borne encephalitis). In addition to climatic factors, regional disease risks are also affected by factors such as land use, vector control, human behaviour, global trade and travel, and public health capacities.

Observed effects

Warmer temperatures have allowed many disease-carrying vectors to expand their distribution northwards and to higher altitudes in Europe. Locally transmitted outbreaks of dengue, chikungunya, West Nile fever and even malaria have occurred in southern and southeastern Europe in recent years (mostly since 2010). Improved climate suitability for the disease vectors have contributed to these outbreaks.

Dengue is mostly leading to a febrile illness, but severe forms include haemorrhagic fevers and death. Locally transmitted dengue cases in continental Europe where A. albopictus is present continue to occur at a greater frequency. Until 2010, Europe had been free of autochthonous dengue transmission since the 1927/28 outbreak in Greece 82 years prior. The first reports of locally contracted dengue cases in recent times occurred in Croatia and France in 2010. Since then, sporadic outbreaks have occurred in 2013, 2014, 2015, 2018, 2019, and 2020 in France, Spain, and Italy. One hypothesis as to why the frequency of these outbreaks seems to be increasing is that climate changes in southern Europe have improved the climatic suitability for A. albopictus. Although average suitability for dengue remained low in Europe, 2018 was the most suitable year yet recorded for both vector species in this region, with a change from the 1950s baseline of 25% for A. aegypti and 60% for A. albopictus. Increasing trends can be observed for all EU countries.

Tick-borne encephalitis (TBE) and Lyme borreliosis (Lyme disease) are the two most important tick-borne diseases in Europe, both of which are transmitted primarily by Ixodes ricinus. Several European countries have reported that Ixodes ricinus have migrated north and to higher altitudes. Lyme has a reported incidence of approximately 65 000 cases per year in the EU per year. The mean annual reporting of TBE cases has increased by approximately 400 % in European endemic areas over the past 30 years, although this is almost certainly the result of more robust detection methods and diagnosis. A high incidence of both diseases is correlated with mild winters and warm, humid summers.

Projected effects

A warming climate is projected to expand the area suitable for the transmission of vectorborne diseases in Europe, mainly northwards. Detailed analyses for West Nile virus infections, dengue and chikungunya suggest that the expansion would occur mainly at the fringes of the current regions of transmission. Under a high emissions scenario during the 21^st century, however, a large part of southern Europe risks being invaded by Aedes aegypti that transmit dengue.

Policy responses

Improvements in public health services may counteract the expansion of disease vectors such as Aedes mosquito vectors in the short- to medium-term, but climate change will make such efforts increasingly difficult and costly. The presence of effective health care systems and changes in land use should be sufficient to prevent malaria from becoming re-established in Europe despite increasing climatic suitability.

References

• EASAC, 2019, The imperative of climate action to protect human health in Europe, EASAC policy report 38, European Academies Science Advisory Council.

• Lillepold, K., et al., 2019, ‘More arboviral disease outbreaks in continental Europe due to the warming climate?’, Journal of Travel Medicine 26(5), p. taz017 (DOI: 10.1093/jtm/taz017).

• Liu-Helmersson, J., et al., 2019, ‘Climate change may enable Aedes aegypti infestation in major European cities by 2100’, Environmental Research 172, pp. 693-699 (DOI: 10.1016/j.envres.2019.02.026).

• Semenza, J. C. and Suk, J. E., 2018, ‘Vector-borne diseases and climate change: a European perspective’, FEMS Microbiology Letters 365(2) (DOI: 10.1093/femsle/fnx244).

• Watts, N., et al., 2021, ‘The 2020 report of The Lancet Countdown on health and climate change: responding to converging crises’, The Lancet 397(10269), pp. 129-170.

• WHO Europe, 2018, Public health and climate adaptation policies in the European Union, World Health Organization Regional Office for Europe, Copenhagen.