Predatory prawns found to control major parasite more effectively than drugs alone

A demonstration project in Senegal, West Africa, has shown that freshwater prawns can serve as an effective natural solution in the battle against schistosomiasis, a parasitic disease that now affects more than 250 million people worldwide.

Published in PLOS Neglected Tropical Diseases, the findings by researchers with Stanford university upend the current status quo of drug-only treatment by showing that ecological tactics such as introducing prawns that prey on parasite-infected snails to local water sources have proven the most effective way to reduce schistosomiasis prevalence.

A drug, praziquantel, was introduced in the late 1970s to help wipe out the infestation of parasitic flatworms that can cause liver failure, bladder cancer and lasting cognitive impairment. Nearly 40 years later, it has yet to make a dent in the global burden of the disease. However, with the drug, environmental interventions such as snail control fell out of favor and became seen as "old-fashioned."

While it has been used successfully to treat millions of people, clearing parasites from those infected with minor side effects for less than 30 U.S. cents a treatment, praziquantel's lasting impact is limited, as treated people often re-enter contaminated water to bathe and clean clothing, among other chores, repeatedly exposing themselves to reinfection.

"We have to examine the drivers of infection and address transmission and reinfection cycles from both the human and environmental angles if we want to make a long-term impact," said Susanne Sokolow, lead author of the study and a research associate at Stanford' s Hopkins Marine Station. "For schistosomiasis control, that means addressing the snails that carry the parasite."

After examining the history of schistosomiasis control strategies in 83 countries and territories, the researchers found programs that used widespread snail control, either alone or in conjunction with drug administration, reduced the proportion of the population infected with the disease by over 90 percent. By comparison, programs that used little or no snail control reduced schistosomiasis prevalence by less than 40 percent.

"Our work adds a crucial piece to the puzzle of effective strategies to fight schistosomiasis," co-author Giulio De Leo, a biology professor at Hopkins Marine Station and a senior fellow at the Stanford Woods Institute for the Environment, was quoted as saying by a news release from the university in northern California.

Sokolow and De Leo lead a team that has pioneered work to curb schistosomiasis' s spread by reintroducing native prawns that eat disease-carrying snails. Preliminary results from a demonstration project in Senegal show that the reintroduction of prawns in pens at river access points led to fewer snails and reduced transmission of schistosome parasites to people.

The team recently launched the Program for Disease Ecology, Health and Environment at Stanford to work on sustainable ecological solutions to a range of diseases. "In the bigger picture, for other diseases that have environmental phases, who knows what creative solutions might exist like we have seen for schistosomiasis?" Sokolow said. "Let' s bring our creativity back to these important problems and think beyond the pills." Endit