Harnessing crayfish, Procambarus clarkii, to eliminate Schistosome transmitting snails in the Mwea irrigation scheme, Kenya.

Abstract

The existence or lack of natural enemies is one ecological aspect that can have a significant impact on the human burden of environmentally transmitted parasite diseases. First discovered in Lake Naivasha, Kenya, in 1970, red swamp crayfish swiftly expanded throughout the area, overlapping with the range of freshwater snails that act as the intermediate host of schistosomiasis, a trematode disease of poverty that affects up to 250 million people worldwide, 9 million Kenyans, and 23.1 % of Mwea. While mass drug administration is practiced, cases of reinfection occur, hence the need to augment control strategies targeting snails. Using baited crayfish traps and a snail scoop, a baseline survey was carried out to map out canals with and without both the predator and the prey. Specifically, snail and crayfish populations were statistically expressed as percentages and proportions. Snail abundance and Infection rates were compared using percentages and proportions. Prior to the introduction of crayfish, in August 2021, 2703 snails that transmit schistosomes were found in the five sites in the Mwea water environment. While in the other regions, Nice had no snails, Mianya (12.3 %) had high infection rates, which were followed by Nguka (12.3 %), Murinduko (6.3 %), and Nineveh (5.0 %). In certain settings, the prevalence of snails dramatically dropped (p ≥ 0.001) following the introduction of crayfish. The five study environments' infection rates did not differ significantly (p ≥ 0.105). Out of the 218 crayfish captured at the six study locations, Nguka had the most (104), ahead of Nice (82) and Mokou (32), indicating relative abundances of 47.7 %, 37.6 %, and 14.7 %, respectively. During the sampling period, there were no crayfish in Mianya, Murinduko, or Nineveh. Our findings imply that ecological factors like vegetation and human activity significantly influence aquatic-based biological control.