Agent of Disease:
Schistosoma are a genus of parasitic flatworms responsible for cases of Schistosomiasis in humans. These helminths can be found all over the world, but are primarily found all over Africa, the Middle East, and Southeast Asia. Schistosomiasis is also known as Bilharzia, and Schistosoma are also called Blood-Flukes. These worms have an incredibly complicated life cycle, spread over four forms and two hosts, and have persisted for thousands of years(signs of Schistosomiasis have been found in mummies).
Here is the life cycle of a successful Schistosoma:
- Schistosoma begin their lives as eggs in still water.
- They hatch into Miracidia, and swim off in search of their first host, a snail.
- Inside snails, they multiply into Cercariae, then leave in search of their final host, a human.
- When they find a human in the water, they burrow through their skin over a period of days. Then they can mature into their final worm form, pair up for mating, and release eggs throughout the body until the eggs make their way out through the urinary and/or digestive tract into more water to start the cycle again.
How it Hurts Us:
Schistosomiasis is a tricky problem for humans. Although they do siphon off our blood, Schistosoma do little to actively hurt us. Our main problems with them comes from their rapid reproduction. As they lay eggs by the thousands each day, the circulatory system brings them all over the body, and they work their way into all of our organs, especially our digestive tract and bladder. Although death isn’t a concern for a long time(Schistosoma live in humans for years), Schistosomiasis is by no means pleasant. It means pain, bloody stool and urine, swelling of the body, impaired growth in children, and organ damage. Fortunately, we have an effective treatment for the infection. Praziquantel is cheap and easy to use, only requiring one dose annually to clear the body of blood-flukes.
Due to it’s complicated life cycle, one would think Schistosoma have a hard time reproducing, but that couldn’t be further from the truth – 200 million people are infected with Schistosomiasis right now. The problem comes from people using contaminated water. When children play games in the water(especially in the hot parts of the world this disease affects), or women do laundry in the water, or someone falls out of a fishing boat, they are at risk. Because thousands upon thousands of Cercariae are swimming around in infested water at any time, no exposure is safe. Mass transmission of the disease comes when sewage systems are underdeveloped, and either someone uses the local lake to relieve themselves, or a latrine overflows and spreads the eggs around again.
Thankfully, there are multiple ways to deal with Schistosomiasis:
- Using drugs like Praziquantel to treat existing cases
- Encouraging people to stay away from the water, and to boil the water they use
- Killing off the snails that help the Schistosoma reproduce
None of these are too difficult on their own, and consequently the biggest problems with treating and fighting Schistosomiasis is access to medical infrastructure. While convincing people to take strange pills and change how they work and play is difficult, Schistosomiasis is a big enough scourge for most people to make the effort, and consequently, the WHO hopes to have eradicated Schistosomiasis by 2020.