Life Cycle of Schistosomiasis Parasite

Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson goes over the lifecycle of an ancient disease that affects people to this day. It's known as schistosomiasis, and you'll learn how it is that people become infected with the parasite that causes this disorder.


Over 5,000 years ago, an ancient Egyptian was infected by a parasite known as a schistosome, and he may have developed some of the signs and symptoms characteristic of a disorder known as schistosomiasis, which is a water-borne infectious disease that affects people in Asia, Africa, and Latin America. The disease is caused by one of a number of different kinds of parasitic worms known as trematodes.

We can't be sure exactly what that ancient Egyptian went through, as many cases of this infection are asymptomatic, but we can be more sure of how he may have been infected with this disease. Find out as we explore the general life cycle of the various parasites involved in schistosomiasis.

Outside of Man

To begin with, someone other than our ancient Egyptian, some other person, was infected with a schistosome at one point. He (or she) eliminated the eggs of this parasite in his feces or urine. Again, how the eggs were eliminated depends on which species of schistosome we're talking about.

Regardless, maybe he peed in a river when he was swimming in it. Who doesn't, right? Right? Or maybe he defecated into a bucket and then washed that bucket in the local water source.

Either way, the eggs of the parasite entered a water source. This caused the larval (baby) forms of the parasite, known as miracidia, to hatch from the eggs. Using their tails, these babies swam about in the water as they looked for a place to call home. That home, the intermediate host in this life cycle, was a snail.

As soon as the larvae found this home, they gleefully bored into the poor snail's tissues and multiplied inside. The next larval stage, known as cercaria, was produced inside the snail as a result. The cercariae are the infective form of the parasite, and they eventually escape the snail and contaminate the water source.

The life cycle of the parasites that cause schistosomiasis.
The life cycle of the parasites that cause schistosomiasis.

Inside of Man

Once in the water source, the cercariae swam around for a few days. If, during this period of time, our ancient Egyptian man decided to take a swim in the water, they would have penetrated his skin. That's how he got infected! Oh, and by the way, the skin doesn't have to be broken due to something like a cut for these parasites to get inside. No, they can secrete chemicals that will allow them to bore through your skin even if it's perfectly healthy and intact.

Once they entered the skin, the cercariae lost their tails and became known as schistosomulae. The schistosomulae entered the man's bloodstream and eventually came to inhabit the blood vessels near the liver, intestinal tract, or urinary bladder. Here, they matured and began to mate and lay eggs. And from here, the eggs were eliminated in the feces or urine, and so the life-cycle was completed.

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