Chris Froome’s Parasite – What is Bilharzia Anyway?

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Chris Froome is an outstanding athlete, despite having apparently suffered repeatedly with schistosomiasis. Image by Brian Townsley: CC BY 2.0

Chris Froome is an outstanding athlete, despite having apparently suffered repeatedly with schistosomiasis. Image by Brian Townsley: CC BY 2.0

About 160 years ago, Theodor Bilharz discovered the cause of a disease that manifested as chronic bloody urine, and thus gave that disease his name.

Although the term bilharzia is still used, today the disease is known as schistosomiasis in medical circles, and the tiny worms that cause it are Schistosoma spp., S. haematobium, S. mansoni; with S. japonicum being the most common.

According to a July 16 Velo News article by Andrew Hood, Tour de France yellow jersey leader, Chris Froome (Team Sky) “has been struggling with bilharzia over the past several seasons.”

Unfortunately, anyone hoping to learn anything about schistosomiasis from that article will come away considerably misinformed.

Bilharzia – The Parasite

The schistosomes are flukes that live in the blood. Male and female worms are typically found in pairs living in the small blood vessels around the bladder or intestine, depending on the species. Mature females deposit eggs in those vessels – eggs which may be swept away by the bloodstream, or may be lodged in blood vessel walls and eventually break through into surrounding tissue. Gradually they make their way through to the bladder lumen where urine collects, or the intestinal lumen, and are thence passed to the outside world with the urine or feces.

A pair of schistosomes magnified many times. The male wraps himself around the long thin female, seen lying diagonally at upper left. Image from Otis Historical Archives of “National Museum of Health & Medicine," CC BY 2.0.

This is a pair of schistosomes magnified many times. The male wraps himself around the long thin female, seen lying diagonally at upper left. Image from Otis Historical Archives of “National Museum of Health & Medicine,” CC BY 2.0.

The eggs do not hatch inside the human body and give rise to more parasites: they need fresh water and a snail host in order to develop. If they find their way into fresh water, the eggs hatch, releasing a microscopic swimming stage of the parasite, which will invade a snail if it finds the right species. Inside the snail, the parasites multiply, eventually releasing many swimming parasites that are now infective to humans.

This is the stage at which Chris Froome would have stepped into the water. He would not have seen the parasites, for they are far too small, but they are attracted to human skin and burrow through it quickly, entering the bloodstream and traveling to the liver. There, they mature for a time before migrating to the blood vessels where they will spend the rest of their lives producing eggs.

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