The Barcelona Institute for Global Health (ISGlobal) has led a research that concludes that changes in the climate of the Atlantic Ocean can serve to anticipate, with several months of margin, the outbreaks of cutaneous leishmaniasis in North Africa.
To develop this work, the center promoted by the "la Caixa" Foundation has collaborated with specialists from the Institut Pasteur of Tunisia, Morocco, and France. The objective has been to analyze this relationship between climate and disease to refine the prediction capacity of outbreaks in this geographical area.
The scientific team has determined that certain climatic patterns that modify the rainfall regime in the region influence, on different time scales, the transmission of leishmaniasis. Thanks to this, they have managed to design a seasonal prediction system capable of anticipating the appearance of outbreaks by up to a year in advance. It is a parasitic pathology that is transmitted through the bite of phlebotomines, small insects known as sand flies.
"Although it generally does not endanger life, it causes lesions and ulcers on the skin that can persist for months or years and leave permanent scars, with a significant physical, psychological, and social impact," they have indicated, while reminding that "each year around one million new cases are estimated worldwide, especially in the Mediterranean basin, the Middle East, Central Asia, and America."
So far, early warning systems for climate-conditioned diseases had been developed mainly in tropical areas, where phenomena like "El Niño" allow forecasts to be made several months in advance. "In temperate regions, on the other hand, the atmosphere was considered much less predictable, which made it difficult to develop similar tools for vector-borne diseases," they have pointed out.
The study, published in the journal 'Science Advances', demonstrates that this limitation can be overcome if two major patterns of climatic variability of the Atlantic are incorporated: the "North Atlantic Oscillation" (NAO, for its acronym in English) and the "Atlantic Multidecadal Variability" (AMV, also for its acronym in English).
Influence of precipitation and the desert
The authors explain that the NAO is an atmospheric phenomenon that regulates winds over the Atlantic and affects winter rains in Europe and northern Africa, while the AMV describes slow changes in the sea surface temperature that last for years or decades. "The results of the study show that the interaction between both patterns modulates precipitation in northern Africa and, indirectly, conditions the evolution of leishmaniasis," they have specified.
Variations in the temperature of the Atlantic surface alter atmospheric circulation and the winds that transport moisture to northern Africa, which impacts precipitation. These rains regulate the development of vegetation in desert ecosystems and, with it, the populations of rodents that act as reservoirs for the parasite.
"As cutaneous leishmaniasis closely depends on this chain of processes, its appearance can also be predicted from the climatic signals of the Atlantic," they have summarized. The ISGlobal researcher and first author of the work, Adrià San-José, has emphasized that "the desert acts as a natural filter that exposes the climatic memory of the Atlantic."
In his opinion, and "being influenced by fewer climatic processes," the desert "allows for much clearer isolation of the Atlantic signal in rainfall patterns." "Thanks to this, we identified a region where rain is surprisingly predictable, the deserts of Tunisia and Morocco, and we demonstrated that this predictability also transfers to an infectious disease," he has highlighted.
With all this information, the team developed a dynamic model that simulates the transmission of the parasite between humans, phlebotomines, and rodents. The tool integrates local temperature and precipitation with atmospheric and Atlantic data, allowing for the prediction of the appearance and intensity of outbreaks of Leishmania major and Leishmania tropica in Morocco and Tunisia up to 12 months in advance.
"It was thought that this type of prediction was only possible in the tropics," reiterated the ICREA researcher from ISGlobal and senior author of the study, Xavier Rodó, who added that "the surprising thing" is that "a source of predictability has also been found in a temperate region" and has been incorporated into a model ready for operational use.