Opinion One Health for fascioliasis control in human endemic areas Santiago Mas-Coma , 1,2, * M. Adela Valero , 1,2 and M. Dolores Bargues 1,2 Fasciola hepatica and F. gigantica are liver flukes causing fascioliasis, a world- wide zoonotic, complex disease. Human infection/reinfection occurs in endemic areas where preventive chemotherapy is applied, because of fasciolid transmis- sion ensured by livestock and lymnaeid snail vectors. A One Health control ac- tion is the best complement to decrease infection risk. The multidisciplinary framework needs to focus on freshwater transmission foci and their environ- ment, lymnaeids, mammal reservoirs, and inhabitant infection, ethnography and housing. Local epidemiological and transmission knowledge furnished by previous field and experimental research offers the baseline for control design. A One Health intervention should be adapted to the endemic area characteris- tics. Long-term control sustainability may be achieved by prioritizing measures according to impact depending on available funds. Fascioliasis: complexity, and impact on communities Fascioliasis is a zoonotic disease caused by two species of liver fluke, Fasciola hepatica and F. gigantica, both originated by speciation derived from F. nyanzae specific to hippopotamuses, after a host capture (see Glossary) phenomenon to sylvatic ruminants. Whereas F. gigantica kept the same freshwater lymnaeid snail species of the Radix group as the vector in southeastern Africa, F. hepatica jumped from the warm-preferring-lowland bigger Radix to cooler-habitat- preferring smaller Galba/Fossaria lymnaeids in Near-Eastern Asia [1]. Animal domestication in the Fertile Crescent allowed F. hepatica and F. gigantica to later expand with domesticated ruminants, equines, and camelids throughout the Old World during the Neolithic, and subsequently colonize the Americas and Oceania with livestock transported with ships in the last 500-year period. Their low host specificity enables them to also infect omnivores such as humans and pigs. In that way, fascioliasis became the only human trematodiasis of worldwide distribution [2]. In the 1990 and 2000 decades, the increasing number of human infection reports and the pro- gressive description of human endemic areas in different continents led the World Health Orga- nization (WHO) to include this disease in the group of foodborne trematodiases among neglected tropical diseases (NTDs) [3,4]. Many aspects add to the importance of human fascioliasis, such as its pathogenicity [5–7], sequelae [6,8], immune-suppression-favoring coinfections with other pathogens during the acute phase [9] and chronic phase [10,11], virulence [12], drug resistance [13], community underdevelopment impact [14,15], impact on children and gender [15,16], lack of premunition and sterile immunity allowing for infection/reinfection of inhabitants living close to a transmission focus inside the typical waterborne patchy disease distribution [17,18], climate change influence [19,20], and anthropogenic modifications of the habitats [21]. Fasciolids appear to rapidly adapt to different mammalian hosts. This may be due to their large genome, characterized by extensive gene duplication, polymorphisms, and high repeat content Highlights In fascioliasis, oligoxenous snail vector specificity, low mammal host specificity, epidemiological situations, transmission patterns, and influencing biotic/abiotic factors underlie high complexity. In human fascioliasis, a One Health ap- proach is the best strategy to comple- ment preventive chemotherapy by decreasing infection/reinfection risk. A One Health multidisciplinarity approach for human fascioliasis includes axes targeting the environment (habitat and climate), snail vectors, mammal reser- voirs, the human host, and ethnography of the inhabitants of the endemic area. Sufficient baseline knowledge about epi- demiology and transmission of fasciolia- sis obtained in previous field surveys and experimental studies is needed. A One Health action should be adapted to the epidemiological and transmission characteristics of the endemic area, and use a pilot area when dealing with large endemic areas. 1 Departamento de Parasitología, Facultad de Farmacia, Universidad de Valencia, Av. Vicente Andrés Estellés s/n, 46100 Burjassot, – Valencia, Spain 2 CIBER de Enfermedades Infecciosas, Instituto de Salud Carlos III, C/Monforte de Lemos 3–5. Pabellón 11. Planta 0, 28029 Madrid, Spain *Correspondence: S.Mas.Coma@uv.es (S. Mas-Coma). Trends in Parasitology, Month 2023, Vol. xx, No. xx https://doi.org/10.1016/j.pt.2023.05.009 1 © 2023 Elsevier Ltd. All rights reserved. Trends in Parasitology TREPAR 2401 No. of Pages 18