The Crustacean Cure for one of the World’s Worst Parasites

by Mark Hay

November 7, 2014
The noble prawn

Schistosomiasis, a.k.a. bilharzia or blood fluke, is a particularly nasty affliction. Stemming from the presence of a parasite in the blood, the illness is one of the world’s 17 neglected tropical diseases. Active mostly in Africa but also in swaths of Asia and Latin America, it afflicts 230 million people every year, killing more than 200,000. Days or months after the waterborne parasites enter one’s body (ironically, the water is still potable—it’s just contact with the skin that allows parasitic transmission), those afflicted develop an itchy rash, fever, chills, coughs, and debilitating aches with no warning. And repeated infections—which are quite common, especially among youth—can lead to lifelong anemia, learning disorders, malnutrition, organ damage, and even seizures, due to spinal inflammation as the body reacts to the presence of blood fluke eggs in its system. In terms of its prevalence and long-term effects, the disease is second in its debilitating capacity to malaria, possibly the most deadly disease in human history. Traditionally, treatment options have been relatively ineffective and quite expensive. But recently, in at least one hard-hit region, a project has developed with potential to totally eliminate schistosomiasis from local communities, while creating sustainable agriculture—all through the clever use of prawns.

Life cycle of the blood fluke

Optimistic global health bodies say we have the power and potential to control and beat back schistosomiasis. After all, the parasite has a very narrow and peculiar lifecycle, infecting freshwater snails for a time before emerging into the water, where they can survive independently for only 48 hours. During that window, the parasites need to get into your blood vessels to lay their eggs for redistribution via urine and feces back into the water system. So if you can keep people out of infected waters long enough, and track and control those with the disease, then you’ve eliminated the parasite from a given area. There’s even a treatment, praziquantel, that can cure an afflicted individual. But given the long wait on stool samples to confirm contamination, the cost of the drugs, the remoteness of afflicted regions, and the long incubation period, it’s just too easy for waters to be re-contaminated even after environmentally harmful chemicals are used to cull the snail population. Some researchers hope they’re on their way to a vaccine, and awareness campaigns and effective treatment distributions have cut down on the number of cases in some communities. But the cycle of infection just keeps on going.

Since the 1980s, villages along West Africa’s Senegal River have grown especially prone to outbreaks and reintroductions of schistosomiasis. After puzzling away for a time, researchers eventually learned this was because the construction of the Diama Dam at the river’s mouth wiped the parasite-carrying snails’ natural predator, the giant African river prawn, out of the ecosystem, allowing infection channels to explode. When she heard this about a decade ago, American public health specialist Elizabeth Huttinger hatched a simple yet brilliant plan: Why not just find a way to reintroduce the prawns to the river? Soon after, Project Crevette (French for “prawn”) launched to do just that.          

Freshwater snail, carrier of the blood fluke

Huttinger and her team paid their first visit to Senegal in 2007, working up a concrete plan which then received funding from the Bill and Melinda Gates Foundation in 2010. After a year of water quality monitoring to make sure that the prawns could survive, Crevette officially launched in 2011. By 2012, they had test projects churning up and down the Senegal and found that their research held up marvelously: Infections reportedly dropped 80 percent with just a few hundred prawns in a water source, and those infected had fewer parasites in their blood, lessening their symptoms. There’s some indication that villages, with proper precautions alongside the prawns, could hit zero infections. Support and praise for Project Crevette flowed in accordingly.          

The reception along the river was equally joyous, but not just because of the decreased infection rates. The prawns, which matured within six months, sold like hotcakes in local markets for five times the price of a fish, adding an extra layer of incentives to care for the prawns, protect their water, and increase their stocks—a hatchery opened in late 2011, training students in prawn care and introduction, and some folks have discussed building means to help the critters migrate past the Diama Dam and survive on their own.

A male blood fluke. Gross.

Now Crevette is once again on the move. They have more than a hundred miles of waterway to stock, and thousands of prawns to release into prepped and willing communities each month. The hopes are that, at its height, the project will release about four million prawns a year, a fifth of which will be fished, adding up to $5 million to the local economy. But perhaps even better than the projections for the Senegal River area, the project may not just be limited to one (albeit especially beset) region of Africa. Huttinger’s work is based on studies using Louisiana crayfish to lower infection rates in Kenya, suggesting that the Crevette process can be repeated (notwithstanding the risks of introducing new species) across dozens more countries afflicted with schistosomiasis. With the help of our shellfish friends, we might just have the little blood flukers beat.

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The Crustacean Cure for one of the World’s Worst Parasites