No abstract

Trematodes are snail-borne parasites of major zoonotic importance that infect millions of people and animals worldwide and frequently hybridize with closely related species. Therefore, it is desirable to study trematodiases in a One Health framework, where human and animal trematodes are considered equally important. It is within this framework that we set out to study the snail and trematode communities in four artificial lakes and an abattoir in Zimbabwe. Trematode infections in snails were detected through multiplex PCR protocols. Subsequently, we identified snails by sequencing a partial mitochondrial cytochrome c oxidase subunit I (COI) fragment, and trematodes (adults from the abattoir and larval stages detected in snails) using COI and nuclear rDNA markers. Of the 1,674 collected snails, 699 were molecularly analyzed, in which we identified 12 snail and 19 trematode species. Additionally, three parasite species were sampled from the abattoir. Merely four trematode species were identified to species level through COI-based barcoding. Moreover, identification of members of the superfamilies Opisthorchioidea and Plagiorchioidea required a phylogenetic inference using the highly conserved 18S rDNA marker, as no related COI reference sequences were present in public databases. These barcoding challenges demonstrate a severe barcoding void in the available databases, which can be attributed to the neglected status of trematodiases. Adding to this, many available sequences cannot be used as different studies use different markers. To fill this gap, more studies on African trematodes, using a standardized COI barcoding region, are desperately needed.

Background Humans impose a significant pressure on large herbivore populations, such as hippopotami, through hunting, poaching, and habitat destruction. Anthropogenic pressures can also occur indirectly, such as artificial lake creation and the subsequent introduction of invasive species that alter the ecosystem. These events can lead to drastic changes in parasite diversity and transmission, but generally receive little scientific attention. Results In order to document and identify trematode parasites of the common hippopotamus (Hippopotamus amphibius) in artificial water systems of Zimbabwe, we applied an integrative taxonomic approach, combining molecular diagnostics and morphometrics on archived and new samples. In doing so, we provide DNA reference sequences of the hippopotamus liver fluke Fasciola nyanzae, enabling us to construct the first complete Fasciola phylogeny. We describe parasite spillback of F. nyanzae by the invasive freshwater snail Pseudosuccinea columella, as a consequence of a cascade of biological invasions in Lake Kariba, one of the biggest artificial lakes in the world. Additionally, we report an unknown stomach fluke of the hippopotamus transmitted by the non-endemic snail Radix aff. plicatula, an Asian snail species that has not been found in Africa before, and the stomach fluke Carmyerius cruciformis transmitted by the native snail Bulinus truncatus. Finally, Biomphalaria pfeifferi and two Bulinus species were found as new snail hosts for the poorly documented hippopotamus blood fluke Schistosoma edwardiense. Conclusions Our findings indicate that artificial lakes are breeding grounds for endemic and non-endemic snails that transmit trematode parasites of the common hippopotamus. This has important implications, as existing research links trematode parasite infections combined with other stressors to declining wild herbivore populations. Therefore, we argue that monitoring the anthropogenic impact on parasite transmission should become an integral part of wildlife conservation efforts. Graphical abstract

Background: Freshwater gastropod-borne trematodes pose a great public health burden and cause major economic losses in the livestock and fish industries. Knowledge on the composition, diversity and ecology of both gastropods and trematodes communities is key to understand disease transmission dynamics and control trematodiases of economic significance. The objective of this study is to investigate the diversity and spatio-temporal ecological trends of gastropod and trematode communities on the Northern shore of Lake Kariba in Zimbabwe, the largest artificial lake in volume worldwide. Methods: A sampling campaign was undertaken at 16 sites along the lake shoreline of Kariba town. Gastropods and water samples were collected monthly during one year. All 2477 specimens were identified, counted and subjected to shedding experiments; infection status was confirmed by the use of a Rapid Diagnostic PCR (RD-PCR). To explain spatio-temporal trends in gastropod and trematode occurrence, water samples were analysed for different physico-chemical parameters including pH, temperature, nitrates and phosphates. Results: Gastropod species collected include Bulinus truncatus, Bulinus forskalii, Gyraulus sp., Pseudosuccinea columella, Radix sp, Physella acuta, Bellamya sp. and Melanoides tuberculata. Bulinus truncatus was found to be infected with trematode species belonging to the families Notocotylidae, Psilostomstidae, Paramphistomidae and Diplostomatidae. A species of the latter family was also found to infect B. forskalii. As previously reported, lymnaeid species P. columella and Radix sp. were both infected with a species belonging to the Fasciolidae family, while Radix sp. was also infected with amphistomes. Conclusions: We confirm the occurrence of new species of gastropods in Lake Kariba and the absence of the previously reported B. pfeifferi and B. globosus. This explains the absence of human schistosome species, but we report the presence of other trematode families that have not been reported in Lake Kariba or Zimbabwe before. Compared to the latest study in 2001, there is a remarkable shift in the gastropod community, which is likely driven by the introduction of exotic gastropod species that are now abundant in the lake.