The deliberate effort to reduce the incidence of Guinea worm (Dracunculus medinensis) in humans has been recently met by a host switch to domestic dogs (Canis lupus familiaris). Decreasing number of human cases yet peculiar epidemiological patterns of dog infections in Chad begs the question what ecological factors allowed for host switching to occur and what facilitates Guinea worm transmission. A novel transmission route associated with dogs is likely and might involve a paratenic host. We discuss the potential factors that led to the host switching event and report on an experiment in which we examined whether fish can serve as transport hosts of D. medinensis and closely related D. insignis. Previous work on fish suggested that they are either resistant to infection or have variable species susceptibility. Briefly, we exposed several species of fish to Dracunculus-infected intermediate host, copepods, and determined the ability of the fish to transmit the infection to a model host, domestic ferret (Mustela putorius furo). Species of fish selected for the study were based on availability and relatedness to species of fish found at sites where dog cases were documented.
We found that more than one species of fish can act as paratenic hosts of both D. medinensis and D. insignis. Transmission of D. medinensis and D. insignis via fish was successful yet small sample sizes caution broad conclusions. The experimental infection of ferrets with both Dracunculus spp. after consumption of fish illustrates a potential novel transmission route likely at play in areas where dog cases are increasing. These results further highlight the importance of current recommendations to cook fish thoroughly, proper disposal of fish entrails, and prevent dogs from consuming fish and discarded fish guts in an effort to decrease the potential transmission of the Guinea worm.