As brightly painted fishing boats putter across the lake and fishermen stand thigh deep in the glittering water hauling their catch, it’s hard to believe a deadly secret lurks beneath the surface.

Schistosomiasis, also called Bilharzia, is a parasitic disease carried by water-dwelling snails. To reproduce, larvae must leave the snails and swim across open water to find their next host: humans. Once inside a person, the larvae develop into adults and lay their eggs. Most pass straight through the body, back into water, where the life-cycle starts again. For the unlucky few, remaining eggs will get trapped in the body, often causing a deadly infection.

Every year hundreds of millions of people are stricken by the neglected tropical disease. In 2014 alone, the World Health Organisation estimated 258 million were affected, and 20,000 died as a result of the disease. As with many tropical diseases, those living in poverty are most vulnerable to infection. Without access to enough safe drinking water, the parasites easily find their way into their human hosts. Those relying on fishing and agriculture for work are also at high risk. Even when treated, workers often find themselves re-infected through constant contact with contaminated water.

Manu Prakesh, a bioengineer from Stanford University, has spent years working in Madagascar testing low-cost microscopes to quickly diagnose the disease. Shocked by the number of children being re-infected, Manu turned to stopping the disease at its source.

Prakesh knew from his studies that parasite larvae have not yet developed a mouth when they leave the snails. This means larvae must speed through the water to reach their next host, and their next meal, fast. If they don’t find a human in less than 12 hours, the larvae will die.

With this in mind, Prakesh and his team set about studying the speedy swimmers. If they can learn how the parasite swims, it might be possible to slow them down and stop them reaching their goal.

The researchers used three different approaches to study the parasite. First, they filmed live larvae using a high-speed microscope. They then produced a mathematical model looking at how the body bent and moved the water, pushing the larvae forwards. Finally, the team turned their maths into mechanics. They created a scaled-up robotic swimmer to teach them everything it could about the unique stroke.

While watching the footage, the team noticed swimmers adopted different strokes in different situations. One stroke in particular caught their attention. When swimming against gravity, the parasite turned its forked tail perpendicular to its body. This changed its entire body shape into a ‘T’.

“This was unlike anything I had seen before,” said Deepak Krishnamurthy, a PhD student in the Prakash Lab and lead author of the study. “When I looked at this parasite, I was fascinated by the fact that it was swimming in a completely different way as compared to any other microorganism I knew about.”

With everything they knew so far about the parasite’s bizarre locomotion, the team set about testing it in robotic form. They even dropped their robots into a tank of sticky, gluey corn syrup. The syrup, 10,000 times more viscous than water, recreates the same physical forces that act on the larvae. Using these models, the team could have their ‘larvae’ trial different swimming strokes. They even raced the robots against each other to find the optimal swim speed.

“In many cases, we try to replicate nature in robots. This was very different,” said Krishnamurthy. “On the face of it, it looks like I’m trying to make a robot that swims like a parasite, but the truth is that it was the exact opposite: I was building a robot to actually understand how the biological parasite swims.”

Using engineering to their advantage, Prakesh and Krishnamurthy hope to finally understand how the parasites reach their human hosts. With this knowledge, we will be one step closer to a solution to a widespread and devastating disease.