It infects over 200 million people worldwide, and is only second to malaria in the economic impact it has on the countries in which it is prevalent, and yet schistosomiasis – also known as bilharzia, or more simply “blood flukes” – is too often neglected. But now, researchers at Stanford might have a found a natural solution to help curb the disease: prawns.
The parasite is a type of fluke worm, which spends half of its life cycle in humans and the other half in freshwater snails. The researchers found that the freshwater prawns feed on the snails, but because the prawns do not get infected by the parasite, the fluke’s complex life cycle is broken. In addition to this, the prawns provide a highly saleable, protein-rich product.
“They are delicious,” said Susanne Sokolow, lead author of the study published in the Proceedings of the National Academy of Sciences, referring to the prawns. “They can [cooperate] with local efforts in the developing world to fight parasitic disease and to foster new aquaculture-based industries.”
The disease is spread by contact with water infected with the parasite, as the fluke worm larvae burrow through people's skin as they bathe and wash in infected rivers. It then enters the bloodstream, where it turns into the adult form and makes its way to the liver, feasting on red blood cells as it goes.
The parasite is unusual in the fact that it has both a male and female form that join together to mate, and the female then releases the eggs, which are either excreted in urine or feces – depending on what form of the disease it is – back into the water source. The eggs then hatch into larvae and seek out a host snail to complete the cycle. It is when all the eggs do not leave the body that causes an immune reaction, giving the symptoms of blood in the urine, swelling of the abdomen and in extreme circumstances infertility, amongst others.
The researchers looked at two villages in Senegal, and tracked the parasite-infected snails and the people living there. In one village, they stocked the river access point with prawns, and in the other they let business occur as usual. Over the next 18 months, they found that the number of infected snails had dropped by an amazing 80% in the village with the prawns, and that the people living in the village had a 50% lower disease burden – measured by the mean number of eggs in a person’s urine.
The researchers think that large-scale damming projects in the region may have had a double effect in increasing the prevalence of the disease. Firstly, by increasing the habitat for the snails, and secondly by stopping freshwater prawns from migrating up and down the river to mate and reproduce. By stocking the rivers with more of the prawns, and introducing prawn ladders like those seen for migrating salmon, the researchers think that they could boost the number of crustaceans.
While schistosomiasis can be cured using the drug praziquantel, the problem is not just the expense of the drug, but that people living in these regions, especially children, are easily reinfected when they next enter the water. The researchers hope that the success of this small-scale trial could be replicated by expanding it to a larger trial, and that if used in conjunction with the drug, they could cut transmission rates dramatically.
Header image credit: Jessica Lucia/Flickr CC BY-NC-ND 2.0