Climate Change Will Reshape Liver Fluke Risk Unevenly Across Africa and Europe, New Index Shows

Fascioliasis, a debilitating zoonotic disease caused by the liver flukes Fasciola hepatica and Fasciola gigantica, has long been treated by veterinary and public health authorities as a problem of broad, slowly shifting geography. A new study published in PLOS Neglected Tropical Diseases challenges that assumption with a continental-scale analysis suggesting that climate change will not push risk in a single direction. Instead, the researchers report, the threat posed by these parasites is likely to decline across most of the two flukes’ ranges while simultaneously intensifying in specific northern European hotspots, including Scandinavia and Iceland, where livestock densities are high. The finding emerges from a novel environmental risk index built from the ground up around the parasite’s biology rather than from statistical correlations alone, and it offers one of the most mechanistically detailed pictures yet of how a warming world may redraw the map of a major neglected tropical disease.

The challenge the research team set out to address is one that has hampered climate-disease forecasting for years. Predictions of how parasitic diseases will respond to climate change often rely on correlative species distribution models, which relate recorded occurrences to environmental variables and then project those relationships into future climates. Such models can perform well within the range of observed conditions but frequently break down when extrapolating to novel climates, and they say little about why a parasite thrives in a given place. For Fasciola, whose transmission depends on a delicate interplay between free-living parasite stages, a molluscan intermediate host, and the availability of surface water, a purely statistical approach risks missing the ecological machinery that actually drives transmission. The new work, led by Tiem van der Deure and colleagues including Samson Mukaratirwa, Mita Eva Sengupta, and Anna-Sofie Stensgaard, was designed to close that gap by grounding every component of the risk estimate in measurable biological processes.

At the heart of the study is a risk index that integrates three distinct components, each capturing one of the environmental requirements for Fasciola transmission. The first is the temperature dependence of the parasite’s transmission itself, quantified from published experimental studies that measured how development, survival, and infectivity of the fluke respond to temperature. The second is climatic suitability for the snail intermediate host, the lymnaeid snails in which the parasite undergoes crucial larval development. The third is the availability of freshwater habitats, the ponds, marshes, drainage channels, and flooded pastures where parasite and snail meet. By combining these three elements, the index reflects the fact that transmission requires all three conditions to be satisfied simultaneously: a suitable temperature regime, a competent snail population, and standing or slow-moving water that connects them.

Building the index demanded an unusually broad assembly of evidence. The researchers drew on thousands of snail occurrence records to characterize where the intermediate hosts can persist, and they combined mechanistic modelling of the parasite’s thermal performance with correlative modelling of the snails’ climatic niches. This hybrid approach allowed the team to capture the temperature-driven physiology of the fluke directly from laboratory and experimental data while still accounting for the broader environmental envelope within which the snail hosts survive and reproduce. The resulting framework is explicitly scalable, meaning it can in principle be applied at finer spatial resolutions or extended to other regions and other host-parasite systems, a flexibility the authors argue is essential for translating continental projections into locally meaningful risk assessments.

When the index was projected under future climate scenarios, the headline result was, in the authors’ words, a general reduction in fascioliasis risk across most of the ranges of the two liver fluke species. That finding may seem counterintuitive in an era when warming is frequently assumed to expand the reach of tropical pathogens. But the biology of Fasciola helps explain it. The parasite’s transmission is optimized within a particular thermal window, and in many parts of Africa temperatures are already at or near the upper end of that range. Further warming pushes conditions beyond the optimum, suppressing the development and survival of parasite stages and degrading the suitability of the environment for the snail hosts. In other words, for much of the current range, climate change is not opening new doors for the fluke but closing existing ones.

The geographical detail of the projections reveals how uneven these changes will be. In the Sahel and West Africa, the transmission risk of Fasciola gigantica is predicted to decrease substantially, driven by temperatures rising above the optimum for parasite transmission and by declining climatic suitability for the intermediate snail hosts. This is a region where fascioliasis imposes a real burden on livestock production and where human cases occur, so a projected decline in environmental transmission potential could carry meaningful economic and public health implications. The authors are careful, however, to frame this as a change in environmental potential rather than a guaranteed decline in disease, since transmission on the ground also depends on factors the index does not capture, such as water management, animal movements, and farming practices.

While much of Africa sees risk recede, the opposite trajectory emerges in the north. The study projects that transmission risk for Fasciola hepatica will increase in parts of Northern Europe, Scandinavia, and Iceland, regions characterized by cold climates that have historically limited fluke development but that are warming rapidly. Crucially, these are also areas with high livestock densities, meaning that an increase in environmental transmission potential intersects with a large and susceptible host population. For farmers and veterinary services in these regions, the results suggest that fascioliasis, already a costly disease of sheep and cattle, may demand greater attention in the decades ahead, with longer transmission seasons and expanded areas of suitability as previously marginal environments become permissive.

One of the most intriguing findings concerns the potential for hybridization between the two fluke species. Fasciola hepatica and Fasciola gigantica can interbreed where their ranges overlap, and hybrids have been documented in several parts of the world, raising questions about altered virulence, drug sensitivity, and diagnostic challenges. The new analysis suggests that the potential for hybridization may decline under climate change, because the geographic overlap between areas highly suitable for transmission of each species is projected to shrink. As the thermal niches of the two parasites are pulled in different directions by warming, the zones where both can transmit effectively may contract, reducing opportunities for the species to meet and interbreed. This adds a subtle but potentially important dimension to forecasts of parasite evolution in a changing climate.

The authors are explicit about the limitations of their framework. The risk index focuses on the environmentally sensitive components of the Fasciola life cycle and therefore does not account for other important determinants of disease, such as local farming practices, husbandry systems, and vertebrate host densities. Water management, irrigation schemes, and the movement of infected animals can all sustain transmission even where environmental suitability declines, while improvements in drainage or anthelmintic treatment can suppress it where the environment is permissive. The index is best understood, then, as a map of ecological potential, a starting point that identifies where the environment is pushing risk up or down and that can be combined with local epidemiological data to produce actionable assessments. The researchers position their work as laying the groundwork for improved local risk assessment rather than as a final word on future disease burden.

Even with those caveats, the study delivers a message that is likely to resonate well beyond the fascioliasis research community: the impact of climate change on parasitic disease will be highly uneven, and in some places it may run in the opposite direction from conventional expectations. For the Sahel and West Africa, the findings hint at a possible easing of one parasitic burden, though the same warming that suppresses the fluke brings other, well-documented stresses. For Northern Europe, Scandinavia, and Iceland, the results serve as an early warning that a disease once confined to warmer latitudes may become an growing concern for high-density livestock systems. By offering a scalable, ecologically informed framework that can be refined with local data, the research provides a template for how mechanistic thinking can sharpen predictions of climate-driven disease change, replacing broad generalizations with a geography of winners and losers that health authorities, veterinarians, and farmers can actually use.

Subject of Research: Climate change impacts on the transmission risk of liver fluke fascioliasis across Africa and Europe

Article Title: Novel environmental risk index reveals uneven impact of climate change on fascioliasis risk across Africa and Europe

Article References: van der Deure, T., Mukaratirwa, S., Chimbari, M., Dube, A., Manyangadze, T., Sengupta, M. E., Kinunghi, S., Mita, R., Walker, J., Nyawanda, B. O., Nogués-Bravo, D., & Stensgaard, A.-S. (2026). Novel environmental risk index reveals uneven impact of climate change on fascioliasis risk across Africa and Europe. PLOS Neglected Tropical Diseases, 20(10), e0013821. https://doi.org/10.1371/journal.pntd.0013821

Image Credits: AI Generated

DOI: 10.1371/journal.pntd.0013821

Keywords: fascioliasis, Fasciola hepatica, Fasciola gigantica, climate change, liver fluke, risk index, snail intermediate host, neglected tropical diseases, Africa, Europe, livestock, hybridization