Impact of Invasive Water Hyacinth (Eichhornia crassipes) on Snail Hosts of Schistosomiasis in Lake Victoria, East Africa

Abstract

Invasive plants may change ecologic conditions to contribute to transmission of human diseases. This study examined whether water hyacinth (Eichhornia crassipes) had an effect on the snails Biomphalaria sudanica and B. choanomphala, hosts of the disease organism Schistosoma mansoni in Lake Victoria, East Africa. Eight 16-m2 enclosures were established in shallow shoreline areas and were paired for water depth, substrate, detrital build up, and distance from rooted vegetation, agricultural runoff, and human activity. In each enclosure, nine randomly selected sediment samples were collected by using a Petite Ponar Dredge, after which 50 water hyacinth rosettes were added to the experimental enclosure within each pair. Six weeks later, nine randomly selected sediment samples were again collected, as were two water hyacinth rosettes from the water column above each sampling point. During the 6 weeks, water hyacinth density had increased from 50 to approximately 2400 rosettes in each enclosure. Adult B. sudanica and unidentified snail egg masses were observed on sampled water hyacinth petioles. Biomphalaria sudanica density was significantly higher in enclosures with water hyacinth (P = 0.034); snail size suggested that this difference was due to passive or active immigration rather than increased reproduction, but snail emigration or greater predation in control enclosures may also have contributed.