Chikungunya is an infectious disease that causes, among other things, severe and prolonged joint inflammation. For a long time, we considered chikungunya, malaria, dengue and Zika to be (sub)tropical diseases that posed little threat to Western Europe. But is that still true? Recent research sheds light on whether climate change is bringing these diseases our way.
Background
Health authorities are concerned about the fact that the habitat of some disease-carrying insects is expanding further and further north. The reason for this expansion is, of course, the higher temperatures caused by man-made and mitigable climate change. Here, I discuss an article that appeared in February in the Journal of The Royal Society Interface 1 about how the tiger mosquito-chikungunya virus combination is responding to these changes and the possible consequences for the risk of infection for people on the European mainland. An interesting detail is that, until now, it has been travellers who have brought the virus in their blood from tropical destinations. Once the virus is here and the mosquito that transmits it is also here, 1+1 is sometimes greater than 2.
This is a stepping stone to the R0 number that we know from the Corona crisis, which indicates how many people you infect on average if you are infected yourself, for example two if R0 = 2. Another reason not to make unnecessary trips to warm destinations. It is also beautiful here and increasingly warm😉.
The article takes a number of steps:
- It was established that two essential figures were missing in order to calculate the risk of infection with the chikungunya virus (CHIKV) transmitted by tiger mosquitoes for people in a particular area.
- The literature was searched for all studies that contained these missing figures or allowed them to be calculated, and 49 studies were found.
- Using these 49 studies, they calculated how long it takes for CHIKV to pass from the tiger mosquito’s intestine into its saliva (extrinsic incubation period (EIP) in the article). After all, the mosquito itself also becomes infected by drinking contaminated blood, which first ends up in its intestines.
- In addition, the percentage of tiger mosquitoes that have CHIKV in their saliva was calculated as a proportion of all infected mosquitoes (vector competence (VC) in the article). This is important because the mosquito infects humans via its saliva.
- These two figures were then entered into the calculation model for the risk of CHIKV infection for people in a specific area. Until now, ‘borrowed’ EIP and VC data from the tiger mosquito-dengue pair had been used.
- By using temperature data from a satellite, it was possible to accurately determine how warm it is every day in many small squares (on the map) of the European mainland.
- By cleverly combining the above data, a map of the European mainland was created, colour-coded to indicate where the chances of infection are low and high.
- This is made even more concrete by a bar chart for each European country, showing for each month of the year the proportion of a country with at least a 95% chance of CHIKV being transmissible. This means that R0 is greater than 1 there. From the coronavirus crisis, you may remember that R0 indicates the average number of people infected by someone who has the virus. If R0 is greater than 1, the epidemic spreads; if R0 is less than 1, the epidemic dies out.
We see that in the Netherlands, the disease is only transmissible in the far south-east in June, while in July and August it is transmissible throughout the country. For the rest of the year, there is less than a 95% chance that R0 will be greater than 1. However, for retired migratory compatriots and the (ultra) rich with second homes in southern Europe, the chikungunya season is considerably longer.
What does a chikungunya infection do to a person?
I base my findings on a complicated literature study from 2024, 2 which I have not critically assessed for quality. What did they find?
The most common symptoms in the acute phase (7-10 days) of the infection were joint pain (90% of cases), muscle pain or fever (88%). 75% of infected individuals developed symptoms. Between 30–40% of patients developed complaints such as joint inflammation, fatigue, stiffness, depression, and sleep and neurological disorders, which persisted for months to several years. Three per 1,000 infected individuals (0.3%) died as a result of the disease.
However, these percentages vary greatly between the general population and high-risk subgroups, such as the elderly or people who already have a disease. The authors caution that, although they explicitly avoided selecting ‘severe cases’, they believe that the figures they report are partly due to the fact that spectacular research results are more likely to be published.
Prevent infection
What can we do ourselves to avoid infection? Remove standing water, where mosquitoes breed. Wear light-coloured clothing with long trousers and sleeves. Use a mosquito net when you sleep. Use mosquito repellent. Do not travel unnecessarily (by plane) to southern regions. If you do go, consider vaccination (available in the United Kingdom since April 2025).
Want to know more?
The website of the European Centre for Disease Prevention and Control (ECDC) contains a recent literature review on the causes of the spread of various (sub)tropical infectious diseases due to higher temperatures, such as changes in the development of the transmitting insects (vectors) and micro-organisms; the habitats of mosquitoes; the periods during which the disease can be transmitted are becoming longer (the ‘blockade’ caused by cold winters is diminishing); the geographical distribution is changing; the number and behaviour of people and animals that can be bitten by mosquitoes is changing; the number of mosquito enemies is decreasing; interruptions in control measures by authorities; influence of non-climate-related factors, such as (changes in) global trade patterns.
Disclaimer
I am a clinical epidemiologist (methodologist) with no great affinity for or knowledge of infectious diseases, let alone tropical ones. So, for example, I am unable to properly assess the significance of a crucial sentence in the article describing what was taken into account in the 49 articles from which the EIP and VC values were derived. For example, attention was paid to the type of mosquito, i.e. the vector (Ae. albopictus, tiger mosquito), where it came from, location type (?), genotype of the mosquito, strain of the mosquito, generation of the mosquito, virus (CHIKV), geographical location of the virus, virus genotype, virus strain, dose of the virus given to the mosquitoes, dose unit, type of laboratory test, number of mosquitoes in the study, temperature (scale), humidity (unit), number of days after infection of the mosquito, % of all fed mosquitoes in which the virus has left the intestines and what criterion was used for this, % of all fed mosquitoes in which the virus is present in the saliva and what criterion was used for this.
The primary focus was on studies in which CHIKV was detected in at least the salivary glands of the mosquito. This was taken as the criterion for transmissibility of the infection.
- Tegar, S., Brass, D. P., Purse, B. V., Cobbold, C. A., & White, S. M. (2026). Temperature-sensitive incubation, transmissibility and risk of Aedes albopictus-borne chikungunya virus in Europe. Journal of The Royal Society Interface, 23(235), 20250707. https://doi.org/10.1098/rsif.2025.0707[↩]
- Rama, K., Roo, A. M. de, Louwsma, T., Hofstra, H. S., Amaral, G. S. G. do, Vondeling, G. T., Postma, M. J., & Freriks, R. D. (2024). Clinical outcomes of chikungunya: A systematic literature review and meta-analysis. PLOS Neglected Tropical Diseases, 18(6), e0012254. https://doi.org/10.1371/journal.pntd.0012254[↩]