The University of Valencia studies coinfections in different environments across several countries and opens up a new field of research

The results open a new field of research, both in experimental coinfection studies using laboratory animals susceptible to Fasciola infection, as well as in surveys in endemic areas and investigations into health consequences, treatment trials and control initiatives.

The study focused on fascioliasis, an emerging parasitic disease that affects 17 million people worldwide. Transmitted by freshwater snails, it is highly pathogenic in humans, causes significant morbidity and can be fatal. The research identified four types of underlying causes, including characteristics of transmission and routes of infection by pathogens, along with immunological, environmental and social factors.

Santiago Mas-Coma highlights his “concern” about the parallels with the situation detected in the area affected by the weather phenomenon known as DANA in Valencia in October 2024, followed by the discovery of numerous pathogens in mud and water — viruses, bacteria, protozoa, free-living pathogenic amoebae, helminths and various vectors transmitting infectious diseases — which consequently posed a risk of coinfections. “The results obtained will allow us to take measures to reduce the risks of coinfections,” the expert explains.

María Adela Valero and Santiago Mas-Coma, who form part of a World Health Organization (WHO) team at the UV, analysed infections in 2,575 untreated individuals in developing countries and diagnosed these conditions over 32 years of surveys. These surveys were conducted in four rural areas with intense and persistent transmission (hyperendemicity) and very different environmental, social, ethnic and religious characteristics in Bolivia, Peru and Egypt.

First author María Adela Valero emphasises the unexpected results: “The rarity of cases of children who did not present any coinfection was striking. Very few children were infected only with Fasciola. The vast majority of children infected with Fasciola were simultaneously infected with other parasites. We diagnosed multiparasitism in children with fascioliasis, who were at the same time infected with up to nine protozoa and as many as five different helminths. The implications for pathogenicity, personal development and even survival are obvious”.

Coinfections with helminths and protozoa in the same individual were analysed to determine whether specific epidemiological patterns exist, including the complexity of coinfections, the risks of multiparasitism, the associations of particular parasites, the implications for pathogenicity and their multidisciplinary causes.

The WHO includes fascioliasis in its list of priority neglected diseases due to its global distribution and its role in causing underdevelopment. This disease has many different transmission patterns, and humans are mainly infected through consumption of freshwater plants and natural drinking water carrying the infectious larval stage released by snail vectors.

Santiago Mas-Coma stresses “the importance of the study, given the great difficulties in conducting field surveys of this kind, as a study like this today is almost unrepeatable”, he explains. The study involved the biomedical research centres (CIBER) for Infectious Diseases and for Epidemiology and Public Health of the Carlos III Health Institute, the Universidad Mayor de San Andrés (Bolivia), the Universidad Peruana Cayetano Heredia, the Universidad Nacional de Cajamarca (Peru) and the U.O.C. Rapporti Internazionali (Italy).

Article: Valero M.A., Morales-Suarez-Varela M.M., Marquez-Guzman D.J., Angles R., Espinoza J.R., Ortiz P., Curtale F., Bargues M.D. & Mas-Coma S., 2025. Helminth/protozoan coinfections in chronic fascioliasis cases in human hyperendemic areas: High risk of multiparasitism linked to transmission aspects and immunological, environmental and social factors. Tropical Medicine and Infectious Disease, 10: 224 (45 pp. + Supplements 1–3). https://doi.org/10.3390/tropicalmed10080224