Climate change could expand chikungunya risk zones: Model points to 139 countries

A study published in the journal Frontiers in Cellular and Infection Microbiology modeled current and future potential transmission zones for the chikungunya virus. The authors used ensemble species distribution models to estimate where climate conditions and mosquito vector distributions could support transmission now and in the future.

The study's key finding: currently, potential risk zones for chikungunya virus transmission cover 21.26% of the world's land area and affect 139 countries and regions. The highest risk zones are currently concentrated in tropical and subtropical regions—South America, Africa, South and Southeast Asia, the Caribbean, and parts of Oceania.

However, climate change may alter the geography of the risk. The model shows a possible expansion of transmission zones into temperate latitudes: northeastern North America, north-central Europe, and East Asia may become more significant surveillance zones by the end of the 21st century. Meanwhile, in some tropical regions, the risk may decrease rather than increase during extreme warming due to heat stress, which reduces the suitability of the environment for mosquitoes.

It's important to understand: this is not a forecast of specific case numbers or a statement that outbreaks will inevitably occur in the countries listed. The study assesses the ecological suitability of the territories for virus transmission: whether the climate is suitable, whether the conditions are conducive to Aedes aegypti and Aedes albopictus mosquitoes, and whether this corresponds to known data on the virus.

Key point	What the study showed
Disease	Chikungunya
Pathogen	Chikungunya virus
Main carriers	Aedes aegypti and Aedes albopictus
Type of study	Modeling the global risk of transmission
Method	Hierarchical ensemble models of species distributions
Current potential risk zone	21.26% of the world's land area
Number of countries and regions at risk	139
Period of future forecasts	2021-2100
DOI	10.3389/fcimb.2026.1808175

Why is chikungunya virus important for public health?

Chikungunya is a viral infection transmitted by mosquitoes of the Aedes genus. The article states that the virus is most commonly transmitted by Aedes aegypti and Aedes albopictus. The disease takes its name from the Makonde language, referring to the characteristic hunched posture of patients suffering from severe joint pain.

Typical symptoms of the acute phase include fever, rash, muscle pain, and severe joint pain. In some patients, the disease does not resolve quickly: a chronic phase may develop with persistent joint pain and other musculoskeletal symptoms.

In terms of global risk, the vector, Aedes albopictus, is particularly important. Unlike Aedes aegypti, it tolerates a wider range of temperatures and is able to establish itself in temperate regions. This is why the chikungunya virus has been able to spread beyond the classic tropical zones and pose a threat to Asia, Europe, and the Americas.

The authors of the article emphasize that climate change alters the ecological niches of vectors. If mosquitoes gain the ability to survive and reproduce in new regions, this creates a potential basis for virus transmission. However, an actual outbreak depends on more than just climate: the introduction of the virus, population density, urban environment, mosquito control, medical preparedness, and the presence of immunity in the population are all important factors.

What makes chikungunya significant?	Explanation
Severe joint pain	May dramatically reduce daily activity
Possible chronic phase	In some patients, symptoms persist beyond the acute period.
Transmission via Aedes	These mosquitoes are already widespread throughout the world.
Climate sensitivity	Temperature and precipitation influence the suitability of the environment for vectors
Risk in new regions	The population of temperate countries may not have immunological readiness
The need for early supervision	New risk zones require mosquito monitoring and diagnostics

How the simulation was conducted

The researchers used data on recorded occurrences of Aedes aegypti and Aedes albopictus mosquitoes from 2015 to 2025 from the Global Biodiversity Information Facility, and data on chikungunya virus cases from 2010 to 2022 from HealthMap. After data cleaning and spatial thinning, the modeling included 1,324 records for Aedes aegypti, 1,948 records for Aedes albopictus, and 1,700 records for chikungunya virus.

The climate data included 19 bioclimatic variables and altitude. For future projections, the authors used 16 climate scenario combinations: four socioeconomic trajectories (SSP126, SSP245, SSP370, and SSP585) multiplied by four global climate models. This allowed them to evaluate not just a single "future line," but a range of possible climate scenarios up to 2100.

The study's methodological feature is a hierarchical approach. First, the scientists modeled the potential distribution of two mosquito vectors, then used the suitability of the environment for these mosquitoes as biological predictors to assess the risk of chikungunya virus transmission. This approach reflects a real-world chain: climate influences mosquitoes, and mosquitoes limit the potential for virus transmission.

To improve reliability, the authors applied 11 modeling algorithms and assembled ensemble models. Performance was assessed using the area under the error curve and true skill statistics. The resulting ensemble models demonstrated high predictive ability: for Aedes aegypti, the area under the curve was 0.949, for Aedes albopictus, 0.934, and for chikungunya virus, 0.909.

Element of the methodology	What was used?
Aedes aegypti data	15,600 original records, 1,324 after cleaning
Data on Aedes albopictus	42,170 original records, 1,948 after cleaning
Chikungunya virus data	13,524 original records, 1,700 after cleaning
Climate variables	19 bioclimatic factors and altitude
Future scenarios	16 combinations of SSP and climate models
Algorithms	11 different models
The final approach	Ensemble modeling with model quality weights

What is known about current risk zones?

According to ensemble model calculations, Aedes aegypti currently has potentially suitable habitat on approximately 9.69% of the world's land surface. The most suitable areas for this vector are concentrated in central South America, the Caribbean region of North America, and the southeastern coast of Africa.

For Aedes albopictus, the potential suitability zone was broader—approximately 13.90% of the global land area. Highly suitable areas include the southeastern United States, southeastern South America, and the southeastern coast of Asia. Moderate and low suitability zones also extend along the Mediterranean, the Gulf of Guinea coast, southeastern Africa, and eastern Oceania.

For the chikungunya virus itself, the model estimated potential transmission zones at 21.26% of the world's land area. High-risk areas include the Caribbean coast of North America, eastern South America, the Gulf of Guinea coast in Africa, and coastal areas of South and Southeast Asia.

At the continental level, the highest risk share for the chikungunya virus was calculated for South America - 83.41%, followed by Africa - 42.67%, Oceania - 41.77%, Asia - 30.69%, North America - 13.60%, and Europe - 6.62%. Among the countries and territories with high exposure, the authors name, for example, Equatorial Guinea, Côte d'Ivoire, Ghana, Madagascar, Liberia, the Philippines, Sri Lanka, Cambodia, Bangladesh, Thailand, Jamaica, Nicaragua, Belize, Puerto Rico, Cuba, Guyana, Suriname, Paraguay, Brazil, and Ecuador.

Indicator	Current model evaluation
Aedes aegypti potential area	9.69% of the world's land area
Potential area of Aedes albopictus	13.90% of the world's land
Potential transmission area for chikungunya virus	21.26% of the world's land area
Number of countries and regions at risk of transmission	139
The continent with the highest risk	South America
Risk share in Europe	6.62%
Risk Share in North America	13.60%

How Climate Could Change the Risk Map

Future projections proved to be heterogeneous: the outcome depends both on the chosen climate scenario and the global climate model. In models with high climate sensitivity, the risk of virus transmission was more often increased, while in models with lower sensitivity, many scenarios showed a decrease in risk. This means that uncertainty is not a technical detail—it is built into the climate problem itself.

The overall spatial signal is as follows: Europe and North America may experience an expansion of potential risk zones, while Africa and Oceania may experience a reduction in suitable zones in some scenarios. The authors identify particularly significant zones of potential expansion in the northeastern United States and southeastern Canada, Chile and Argentina, north-central Europe, China, Japan, and North Korea.

At first glance, it might seem strange that warming could reduce the risk in some areas. However, mosquitoes have thermal limits. The article discusses how, when physiological temperature ceilings are chronically exceeded, vector populations can decline. For Aedes aegypti and Aedes albopictus, the discussion cites approximate upper limits of approximately 35°C and 32°C, respectively. Therefore, in some tropical regions, extreme warming could worsen conditions for mosquito vectors.

The dynamics of the Sahel are particularly interesting. The model describes a "first expansion, then contraction" trajectory: moderate initial warming may temporarily improve conditions at the edges of current risk zones, but with more intense warming by the end of the century, these areas could move beyond the mosquito optimum.

Region	Possible future dynamics
Northeastern North America	Expanding potential risk
North-Central Europe	Expanding potential risk
East Asia	Expanding potential risk
The Mediterranean coast of Europe	Some forecasts suggest a possible decline
Northern Australia	Possible reduction in certain scenarios
Sahel	Early expansion followed by contraction during strong warming
Tropical cores of risk	In certain scenarios, heat stress for vectors is possible

Why mosquitoes played a decisive role

One of the most important findings of the study was that viral risk was found to be largely vector-dependent. Environmental suitability for Aedes albopictus explained 72.47% of chikungunya virus distribution, while environmental suitability for Aedes aegypti accounted for an additional 11.92%. Together, these two vectors accounted for approximately 84% of the model's explanatory power for the virus.

This means that climate affects risk not only directly but also through vectors. If a region becomes suitable for Aedes albopictus or Aedes aegypti, then the virus's introduction creates a potential ecological basis for local transmission. If mosquitoes cannot survive sustainably, the risk of transmission is limited, even if the virus is introduced by travelers.

For Aedes aegypti, the key variables were isothermality, temperature seasonality, and altitude. For Aedes albopictus, isothermality, precipitation in the wettest month, and the average temperature of the driest quarter were important. This highlights that even closely related vectors respond differently to climate.

Aedes albopictus deserves special attention because it tolerates a wider range of climate conditions and plays a significant role in the potential spread of the risk to temperate regions. The model shows that environmental suitability for this vector was the largest factor in the virus's distribution, making monitoring Aedes albopictus particularly important for countries that have not previously considered chikungunya a priority threat.

Factor	Contribution to the model
Environment suitability for Aedes albopictus	72.47%
Environment suitability for Aedes aegypti	11.92%
Average temperature of the wettest quarter	9.89%
Temperature seasonality	1.89%
Seasonality of precipitation	1.48%
Altitude	0.75%
The combined contribution of two carriers	about 84%

What does this mean for Europe, North America and East Asia?

The authors specifically highlight temperate regions as new areas of focus. According to their forecasts, north-central Europe, the northeastern United States, and East Asia could become priority areas for monitoring by 2040. This is because warming may weaken the previous low-temperature constraints on mosquito vectors.

Moreover, it was in Europe and eastern North America that the uncertainty between climate models was particularly high. This is logical: these regions are on the edge of ecological suitability, and even small differences in winter temperature forecasts can change the conclusion about whether Aedes albopictus will be able to survive the winter and establish itself.

For healthcare systems, the key is not panic but preparation. If a region becomes potentially susceptible to a vector, entomological surveillance, clinician training, laboratory diagnostics, genomic virus monitoring, and mosquito control programs must be developed in advance. The authors explicitly recommend that countries at moderate risk levels strengthen such measures by 2040.

A separate issue is the population's low immunological preparedness. In regions where chikungunya has previously been virtually absent, the population lacks widespread natural immunity. This can increase the risk of large outbreaks when three conditions combine: the presence of a carrier, the virus's importation, and inadequate public health preparedness.

Region	Why is it important?
North-Central Europe	Possible expansion of ecological suitability
UK and Germany	The authors provide examples of regions for early surveillance.
Northeastern United States	Potential risk expansion area
Southeastern Canada	Mentioned among areas of potential expansion
China and Japan	East Asia highlighted as an area of future focus
North Korea	Indicated among the territories for possible expansion
Temperate regions in general	May be vulnerable due to low immunological readiness

Limitations of the study

The first limitation is related to the source data. The authors acknowledge that mosquito and virus records may be uneven: the Global Biodiversity Information Facility provides better coverage of Europe and North America, while HealthMap may underrepresent data from Africa and Southeast Asia. Spatial cleanup reduces this bias, but does not eliminate it completely.

The second limitation is the two-stage structure of the model. First, the suitability of the environment for mosquitoes is predicted, then these predictions are used as input for the virus. The authors used an ensemble approach to reduce error accumulation, but it is impossible to completely eliminate the transmission of uncertainty from the first stage to the second.

The third limitation is the assumption of stable relationships between the virus, vector, and climate. In the real world, viruses can evolve, and mutations can alter their adaptability to different mosquito species. The article explicitly notes that such unpredictable eco-evolutionary processes are not included in the model.

The fourth limitation is the emphasis on bioclimatic factors. The model did not fully incorporate anthropogenic factors such as urbanization, population growth, mobility, water supply quality, water storage, sanitation, and the ability of the healthcare system to control vectors. Therefore, the results are best understood as a climatically and ecologically validated map of potential risk rather than as a ready-made forecast of future disease incidence.

Limitation	Why is this important?
Unevenness of the initial data	Some regions may be better or worse represented.
Possible underestimation of Africa and Southeast Asia	HealthMap data may not reflect all actual events.
Two-stage model	Mosquito forecast error may impact virus forecast
Unaccounted evolution of the virus	Mutations can change the virus's ability to transmit
There is no complete accounting of urbanization	The urban environment has a strong influence on Aedes mosquitoes.
There is no forecast for the number of cases	The model shows the suitability of the environment, not the future incidence of disease

The main conclusion

The study shows that climate change may not simply "increase" the risk of chikungunya, but redistribute it. In some regions, particularly in temperate latitudes, conditions may become more suitable for virus transmission. In others, particularly in some tropical zones during extreme warming, the suitability of the environment for mosquitoes may decrease due to a shift beyond physiological temperature limits.

The most practical part of the work is the identification of future early surveillance zones. North-central Europe, northeastern North America, and East Asia are identified as regions where it makes sense to strengthen Aedes mosquito monitoring, laboratory readiness, physician training, and vector control programs by 2040.

However, the article doesn't prove that large outbreaks will necessarily occur in all these regions. Real transmission requires virus importation, sufficient vector density, suitable urban and social conditions, and insufficient mosquito control. Therefore, the main conclusion is not one of panic but of management: risk maps are needed to plan preventative measures in advance, rather than react only after outbreaks begin.

News source: Qianqian Zhang, Ling Zhang, Yuchang Ma, Ziyi Jiang, Yuhe Si, Tianxing Zhang, Binbin Jin, Fangfang Tao, Yang Wu, Ye Xu. Predicting the global risk of chikungunya virus under climate change using ensemble species distribution models. Frontiers in Cellular and Infection Microbiology, 2026;16. DOI: 10.3389/fcimb.2026.1808175.