Beyond the reservoir: rethinking wildlife contributions to Fasciola transmission in multihost landscapes

Abstract

Wildlife infection with Fasciola spp. has been documented across diverse mammalian taxa and ecological settings; however, the epidemiological significance of these infections remains difficult to determine. Serological exposure, parasite DNA, adult fluke recovery, coproantigen detection, and egg shedding represent different diagnostic states and support various levels of inference. In Fasciola transmission, a patent definitive host is only one part of an indirect cycle that also requires eggs to reach wet or aquatic habitats, compatible lymnaeid snails to become infected and amplify the parasite, and susceptible hosts to ingest the viable metacercariae. From this critical perspective, we ask when wildlife infection actually contributes to persistence or transmission to a defined target population. We used the wildlife reservoir paradox to describe situations in which measured wildlife infection is poorly aligned with the realised transmission contribution, and distinguished four context-dependent functions: incidental hosts, amplifying contributors, interface connectors, and maintenance components. We then evaluated how lymnaeid identity and ecology, environmental and hydrological connectivity, and molecular evidence could strengthen or limit reservoir attribution. Finally, we refined Fasciola Interface Management (FIM) into an operational five-step workflow that asks who contaminates, where snail amplification occurs, which target populations are connected to those sites, where parasite flow can be disrupted, and whether transmission subsequently declines. The central argument is that wildlife reservoir status should be attributed to populations within defined transmission systems, not inferred from host positivity alone.