Alternative transmission pathways for guinea worm in dogs: implications for outbreak risk and control

[Display omitted] •Recent evidence suggests that frogs may act as paratenic hosts for the Guinea worm, Dracunculus medinensis.•Dogs may acquire the parasite through consumption of infected copepods or frogs that recently consumed infected copepods.•Tadpoles reduce transmission relative to when tadpoles do not eat copepods or when frogs do not contribute to transmission.•Transmission via frogs may help maintain transmission should direct consumption transmission chains break.•Most effective intervention strategies could focus on the reduction of the number of copepods. Guinea worm (Dracunculus medinensis) has exerted a high human health burden in parts of Africa. Complete eradication of Guinea worm disease (dracunculiasis) may be delayed by the circulation of the parasite in domestic dogs. As with humans, dogs acquire the parasite by directly ingesting infected copepods, and recent evidence suggests that consuming frogs that ingested infected copepods as tadpoles may be a viable transmission route (paratenic route). To understand the relative contributions of direct and paratenic transmission routes, we developed a mathematical model that describes transmission of Guinea worm between dogs, copepods and frogs. We explored how the parasite basic reproductive number (R0) depends on parameters amenable to actionable interventions under three scenarios: frogs/tadpoles do not consume copepods; tadpoles consume copepods but frogs do not contribute to transmission; and frogs are paratenic hosts. We found a non-monotonic relationship between the number of dogs and R0. Generally, frogs can contribute to disease control by removing infected copepods from the waterbody even when paratenic transmission can occur. However, paratenic transmission could play an important role in maintaining the parasite when direct transmission is reduced by interventions focused on reducing copepod ingestion by dogs. Together, these suggest that the most effective intervention strategies may be those which focus on the reduction of copepods, as this reduces outbreak potential irrespective of the importance of the paratenic route.