Researchers have found that temperature changes in the Atlantic Ocean may help predict year to year changes in cutaneous leishmaniasis transmission in North Africa, offering new opportunities for disease forecasting in Morocco and Tunisia.
The study links ocean temperatures, atmospheric circulation desert rainfall and ecological changes that affect the spread of the parasitic disease. The findings suggest that climate signals originating in the Atlantic can influence disease transmission months later.
Cutaneous leishmaniasis is a vector-borne disease transmitted by infected female sandflies. It causes skin lesions and ulcers that can persist for months or years. Although the disease is rarely life threatening and may resolve without treatment, it can leave permanent scars and cause lasting psychological and social harm. Around one million cases occur worldwide each year.
In North Africa, the disease is often caused by the parasite Leishmania major, which survives in animal reservoirs, particularly rodents living in dry environments near villages. Another form, Leishmania tropica also circulates in Morocco, where humans are the main reservoir.
Researchers explained that desert shrubs play an important role in the disease’s transmission. These salt tolerant plants provide food and shelter for rodents, while rodent burrows beneath or near the vegetation create suitable habitats for both rodents and sandflies.
Rainfall can therefore influence disease transmission through a chain of ecological changes. Increased rainfall encourages desert vegetation to grow, potentially supporting larger rodent populations and creating favourable conditions for sandflies. These changes can increase opportunities for the parasite to spread.
The researchers investigated whether North Africa’s climate patterns could help forecast disease transmission months in advance. Seasonal climate forecasting has often focused on tropical regions, where phenomena such as El Niño can produce climate signals that remain predictable for months or longer.
However, rainfall is generally difficult to predict because it depends on several interacting factors, including land sea interactions, mountains and atmospheric moisture.
North Africa’s arid regions offer a potentially different situation. With fewer competing rainfall generating processes, local precipitation is strongly influenced by large scale westerly winds that carry moisture inland from the Atlantic Ocean. The desert environment can make this influence easier to identify.
The study found that slowly changing Atlantic temperatures affect atmospheric circulation and the strength of westerly winds. These winds transport moisture towards North Africa, influencing rainfall in areas where leishmaniasis occurs. Rainfall then affects desert vegetation, rodent populations and the environmental conditions in which sandflies thrive.
These connected changes can ultimately influence the transmission of cutaneous leishmaniasis, allowing researchers to link variations in Atlantic climate conditions with disease patterns across the region.
The findings are significant because they indicate that long range climate predictability may extend beyond tropical regions. Deserts could be particularly useful for identifying such connections because their arid conditions reduce the influence of other processes that might obscure the climate signal.
The researchers said the results could help lay the groundwork for forecasting cutaneous leishmaniasis in Morocco and Tunisia. Advance warnings could allow public health authorities to strengthen disease surveillance, plan sandfly control measures and prepare healthcare services before transmission increases.
However, whether the same forecasting approach can be applied to other diseases and regions will depend on how closely local disease ecology is linked to rainfall and climate conditions.