Project Results

In two trials, using variations of well-established methods, observed feeding on dsRNA-expressing bacteria had no evident effect on viability, behavior, reproduction or embryonic development of the snail Biomphalaria glabrata, compared to feeding on bacteria carrying an empty expression plasmid. Attempts to detect bacterial dsRNA content were thwarted, so it remains unclear whether feeding RNAi works in B. glabrata. Further efforts will aim at assessing bacterial RNA content. Meanwhile, other workers have identified a promising approach to schistosomiasis vector snail population control.

About This Project

Schistosomiasis is a disease transmitted by snails, responsible for chronic illness of many millions of the world's poorest people, mainly in Africa. This project tests the efficacy of RNAi, a targeted genetic weapon, to kill the snails and thus curtail the spread of the disease. RNAi acts only on specific gene sequences, making it environmentally benign and preventing the evolution of resistance in snail populations. Importantly, this snail-killing material would be very cheap to produce.

Ask the Scientists

What is the context of this research?

Schistosomiasis is a debilitating chronic disease afflicting many millions among the poorest people in over seventy tropical nations, mainly in sub-Saharan Africa. The parasitic flatworms (schistosomes) that cause the disease are transmitted by several species of aquatic snails. Where there are none of these snails, the parasite cannot be passed between humans. Chemical molluscicides (snail-killing poisons) played a large part in eradicating schistosomiasis in Japan and Tunisia. These poisons are however quite toxic to other wildlife and humans, and their widespread use is not recommended. Other approaches (parasite-killing drugs, draining wetlands) also have drawbacks. RNA interference (RNAi) is a new option for a 'magic bullet' against snails, cheap enough for large-scale use (1,2).

What is the significance of this project?

We are testing a new method to induce RNAi in snails. RNAi is a natural mechanism of specific gene inactivation: when an animal's body cells encounter double-stranded RNA (dsRNA) that closely matches one of the animal's own gene sequences, that gene gets temporarily shut down.

In many species, dsRNA ingested with food triggers an RNAi response throughout the body. This ‘feeding RNAi’ method is being widely explored as a method of pest control. Biomphalaria glabrata, a major snail vector of schistosomiasis, is susceptible to RNAi: even bathing snails in dsRNA solutions results in specific gene silencing in multiple tissues (3). The proposed study is aimed at finding out if feeding RNAi may be equally effective. If so, it could be a powerful weapon against snail populations.

What are the goals of the project?

Bacteria engineered to produce dsRNA matching several DNA sequences of essential snail genes will be incorporated (alive or dead) into yummy snail chow. Control chow will be made with non-snail DNA. Adult B. glabrata fed on these chows will be assessed for viability, egg-laying, and embryonic development of offspring. Successful gene inactivation should ultimately be lethal to offspring and adults. Further experiments will test feeding RNAi in conditions simulating the dry and rainy seasons common in tropical wetlands.