Unintended Consequences, Serendipity, and Prawns

By ThinkReliability Staff

The Diama dam in Senegal was installed to create a freshwater reservoir. Unfortunately, that very dam also led to an outbreak of schistosomiasis. This was an unintended consequence: a negative result from something meant to be positive.   Schistosomiasis, which weakens the immune system and impairs the operation of organs, is transmitted by parasitic flatworms. These parasitic flatworms are hosted by snails. When the dam was installed, the snails’ main predators lost a migration route and died off. Keeping the saltwater out of the river allowed algae and plants that feed the snails to flourish. The five why analysis of the issue would go something like this: The safety goal is impacted. Why? Because of an outbreak of schistosomiasis. Why? Because of the increase in flatworms. Why? Because of the increase in snails. Why? Because of the lack of snail predators. Why? Because of the installation of the dam.

Clearly, there’s more to it. We can capture more details about this issue in a Cause Map, or visual form of root cause analysis. First, it’s important to capture the impact to the goals. In this case, the safety goal is impacted because of a serious risk to health and the environmental goal is impacted due to the spread of parasitic flatworms. The customer service goal (if we consider customers as all those who get water from the reservoir created by the dam) is impacted due to the outbreak of schistosomiasis.

Beginning with the safety goal, we can ask why questions. Instead of including just one effect, we include all effects to create a map of the cause-and-effect relationships. The serious risk to health is caused by the villagers suffering from schistosomiasis, which can cause serious health impacts. The villagers are infected with schistosomiasis and do not receive effective treatment. Not all those infected are receiving drugs due to cost and availability concerns. The drugs do not reverse the damage already done. And, most importantly, even those treated are quickly reinfected as they have little choice but to continue to use the contaminated water.

The outbreak of schistosomiasis is caused by the spread of parasitic flatworms, which carry the disease. The increase in flatworms is caused by the increased population of snails, which host the flatworms. The snail population increased after the installation of the dam killed off their predators and increased their food supply.

Many solutions to this issue were attempted and found to be less than desirable. Administering medication for treatment on its own wasn’t very effective, because (as described above) the villagers kept getting reinfected. The use of molluscicide killed off other animals in the reservoir as well. Introducing crayfish to eat the snails was derided by environmentalists as they were considered an invasive species. But they were on the right track. Now, a team is studying the reintroduction of the prawns which ate the snails. During the pilot study, the rates of schistosomiasis decreased. In addition, the prawns will serve as a valuable food source. This win-win solution is an example of serendipity and should actually return money to the community. Says Michael Hsieh, the project’s principal investigator and an assistant professor of urology, “The broad potential of this project is validation of a sustainable economic solution that not only addresses a major neglected tropical disease, but also holds the promise of breaking the poverty cycle in affected communities.”

Introducing animals to get rid of other animals can be problematic, as Macquarie Island discovered when they introduced cats to eat their exploding rodent population who ate the native seabirds). (Click here to read more about Macquarie Island.) Further research is planned to ensure the project will continue to be a success. To learn more about the project, click here. Or, click “Download PDF” to view an overview of the Cause Map.