More than meets the eye: A shift in the gastropod and trematode communities in Lake Kariba, Zimbabwe

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.