Cambio climático y enfermedades desatendidas: Evaluación del impacto del cambio climático sobre el riesgo de transmisión de la Fascioliasis en diferentes escenarios ambientales

Climate plays a key role in shaping the dynamics of infectious diseases, and climate change is already influencing the occurrence, transmission, and geographical distribution of many vector-borne diseases (VBDs). Because their invertebrate vectors are highly sensitive to climatic conditions, VBDs are particularly vulnerable to climatic shifts that modify vector distribution and transmission ranges. Fascioliasis, a neglected disease caused by two liver flukes (Fasciola hepatica and Fasciola gigantica) and affecting humans and herbivorous mammals, exemplifies this vulnerability due to the strong dependence of its developmental stages and freshwater snail vectors on climatic and environmental characteristics. Despite the recognized influence of climatic and anthropogenic drivers on fascioliasis transmission, their role in shaping the geographical spread of the disease has been poorly documented and remains difficult to quantify. This doctoral thesis tackles this gap by evaluating how climate change has influenced the risk of fascioliasis transmission in regions that have experienced emergence or re-emergence events. This was addressed through five research articles analyzing long-term climatic trends and transmission-risk indicators across regions where human or animal fascioliasis has emerged or expanded geographically. Two studies focused on the hyperendemic human fascioliasis area of the Northern Bolivian Altiplano, where recent field surveys detected lymnaeid vector populations beyond historically recognized endemic limits. The first study assessed whether climate change underlies this geographical expansion of the infection risk, revealing a notorious climatic shift affecting most of the hyperendemic area. Rising temperatures enabled vector expansion to higher altitudes, while decreasing precipitation may intensify transmission through increased reliance on permanent water bodies. A second study revealed a pronounced climatic heterogeneity within this apparently homogeneous endemic region, closely linked to local topographic features, underscoring the importance of physiography and continuous monitoring when assessing climate-driven disease dynamics. A third study examined the southward expansion of animal fascioliasis in Argentinean Patagonia, providing evidence that regional warming has enabled transmission at increasingly southern latitudes previously considered climatically unsuitable. The following two studies analyzed the emergence of human fascioliasis in Vietnam and India, where a growing number of human cases is being described in the recent decades. The findings demonstrate that the increasing number of case reports is driven by a combination of anthropogenic factors and climatic trends. Finally, a sixth article critically reviews ecological niche modelling (ENM) as a complementary framework to empirical climatic forecast indices, highlighting its value for assessing the geographic transmission risk of VBDs under changing environmental conditions. Together, these studies demonstrate that climate change is a key driver of fascioliasis emergence and geographical expansion, while underscoring the need for integrative approaches to disease-risk assessment.