Blood Worms in Humans

Fact Checked

According to the World Health Organization, schistosomes, or blood worms, kill as many as a million people annually. Because these flukes are endemic to tropical areas, people living in more temperate climates are unaware of the danger these parasites pose.

Primary Host

The schistosoma reproduces in the human body. Production of 200 to 2,000 eggs per day damages blood vessels


Blood vessels break and eggs are discharged into the intestine or urinary track. Infected feces or urine, not properly treated, ends up in water sources.

Intermediate Host

The egg produces the larval form of the parasite. It seeks freshwater snails as an intermediate host and divides into thousands, which are expelled into the water.


Humans swimming or working in infected water contact a schistosoma, which bores into an artery and travels to the intestine or bladder to reside.

Symptoms and Treatment

Early symptoms include abdominal pain and diarrhea. If you suspect exposure and manifest these symptoms, see a doctor immediately.