Domestic pig prioritized in one health action against fascioliasis in human endemic areas: Experimental assessment of transmission capacity and epidemiological evaluation of reservoir role

The Northern Bolivian Altiplano is the human fascioliasis hyperendemic area where the highest prevalences and intensities in humans have been reported. Preventive chemotherapy was implemented in the last ten years. Surveillance showed high human infection and re-infection rates in between the annual triclabendazole monodose treatments. A complementary One Health control action was launched to decrease the infection risk. Among the multidisciplinary axes, there is the need to establish animal reservoir species priorities for a more efficient control. Laboratory and field studies were performed for the first time to assess the Fasciola hepatica transmission capacity of the pig and its potential reservoir role. The experimental follow-up of altiplanic pig isolates through altiplanic Galba truncatula snail vector isolates were performed at different miracidial doses and different day/night temperatures. Experiments included egg embryonation, miracidial infectivity, lymnaeid snail infection, intramolluscan larval development, cercarial production, chronobiology of the cercarial shedding, vector survival to infection, metacercarial infectivity of mammal host, and adult stage development. Surveys included the assessment of prevalence, intensity, egg measurements and egg shedding rates in nature. Pig contribution was evaluated by comparing with the main altiplanic reservoirs sheep and cattle. Results demonstrated that the pig assures the whole F. hepatica life cycle and participates in its transmission in this area. The fast egg embryonation, high cercarial production, long multi-wave shedding chronobiological pattern in monomiracidial infections at permanent 20 °C temperature, and the high daily egg outputs per pig are worth mentioning. The high infection risk suggests early infection of freely running piglets and evolutionary long-term adaptation of the liver fluke to this omnivorous mammal, despite its previously evoked resistance or non-suitability. Genetic, physiological and immune similarities with humans may also underlie the parasite adaptation to humans in this area. The pig should be accordingly included for appropriate control measures within a One Health action against human fascioliasis. The pig should henceforth be considered in epidemiological studies and control initiatives not only in fascioliasis endemic areas with human infection risk on other Andean countries, but also in rural areas of Latin America, Africa and Asia where domestic pigs are allowed to run freely.