Cutaneous leishmaniasis: using the Atlantic climate to forecast outbreaks
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3 key takeaways:
- Cutaneous leishmaniasis is a parasitic disease transmitted by biting insects that affects thousands of people in North Africa every year.
- Two major North Atlantic climate phenomena modulate rainfall patterns in North Africa, affecting vector and rodent populations and generating periods of high or low disease incidence.
- By incorporating these climate signals into a mathematical model, scientists can anticipate certain outbreaks up to 12 months in advance, paving the way for early warning systems for public health authorities.
Cutaneous leishmaniasis is a parasitic disease transmitted by tiny biting insects known as sandflies that causes persistent skin lesions. It affects thousands of people in North Africa every year.
There are two forms of Leishmania parasite. Leishmania major initially circulates between wild rodents and sandflies before accidentally infecting humans. It is widespread in Morocco and Tunisia. Leishmania tropica is spread directly between humans by sandflies, mainly in Morocco.
Why is climate key to understanding leishmaniasis outbreaks?
The link between climate and leishmaniasis is well known – temperature and rainfall influence sandfly populations, vegetation and also rodents, which are animal reservoirs for Leishmania major parasites. But this knowledge had not previously been put to use to forecast health crises.
A recent study has unlocked this potential.
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How does the Atlantic Ocean climate influence disease outbreaks in North Africa?
Rainfall is known to play a key role in leishmaniasis transmission. It influences vegetation and vector and rodent populations, and this in turn affects the number of cases of leishmaniasis that will occur several months later. The latest study goes further by tracing the origin of the rainfall.
The scientists show that two major North Atlantic climate phenomena, North Atlantic Oscillation (NAO) and Atlantic Multidecadal Variability (AMV), modulate rainfall patterns in North Africa. "The combination of the two phenomena generates multiannual periods with high or low incidence of leishmaniasis," explains Richard Paul, Head of the Ecology and Emergence of Arthropod-Borne Pathogens Unit at the Institut Pasteur. The link is clearer in Morocco than in Tunisia, where the relationship between climate, local rainfall and epidemic dynamics is more complex.
North Atlantic Oscillation (NAO): a natural climate phenomenon that describes variations in atmospheric pressure between Iceland and the Azores. The changing pressure gap influences weather in the North Atlantic and Europe.
Atlantic Multidecadal Variability (AMV): a phenomenon that influences climate conditions over decades-long cycles on several continents around the North Atlantic.
How accurately can we forecast an outbreak?
To measure this predictive capability, the scientists developed a mathematical model applicable to both forms of leishmaniasis in the two countries. "By incorporating local temperature, rainfall and Atlantic climate signals, this model can predict certain outbreaks up to six months in advance for L. major in Morocco, and up to 12 months in advance for L. tropica," adds Richard Paul. This represents a significant breakthrough, providing public health systems with an effective early warning system.
Source:
Coupled Atlantic atmosphere-ocean variability modulates cutaneous leishmaniasis in North Africa, enabling long-lead seasonal forecasts, Science Advances, August 19, 2026
Research on cutaneous leishmaniasis and predicting outbreaks of vector-borne diseases comes under the scientific priority "Environmental transition & health" in the Pasteur 2030 Strategic Plan.