Schistosomiasis: It's no fluke!

It's southern China and a perfect afternoon for a quick swim in the tame-looking canal. But lurking down below may be a tiny worm parasite called a blood fluke that can cause big problems. If water doesn't move sufficiently, it could be the perfect home for a type of snail that plays host to the blood flukes. When people enter the water, their skin comes into contact with the larvae. The result may not be pretty.

The blood fluke that causes so much suffering. The Schistosomiasis Control Initiative combats schisto among school-age children and women Source: www.schisto.org

SCHISTOSOMIASIS: THE BASICS

Symptoms

• Within days of infection: rash or itchy skin may appear. Many people have no symptoms in the early phase.
• Within one-two months: late afternoon fever, chills, cough, muscle aches.
• People with repeat infections: tenderness or swelling around the liver, blood in the stool or urine, and possible damage to liver, intestines, lungs, and bladder.

• Occurs in many tropical and subtropical regions around the world (Africa, South America, the Caribbean, Middle East, southern China, and southeast Asia). Not yet found in the U.S.
• Infects as many as 200 million people each year. Of these, 20 million are severely infected.
• Second (to malaria) most common disease caused by a parasite.

• Tiny, parasitic flatworms known as blood flukes (source)
• Blood flukes lay eggs in humans. If eggs end up in water, larvae hatch and infect snails, which becomes the intermediate host.
  
  

  Schistosoma eggs that live inside infected people Source: CDC

  
  
• The blood flukes mature within the snail (takes about a month) and then mature larvae escape into the water (survive for 48 hours).
• Tiny, parasitic flatworms known as blood flukes (source)
• People wade or bathe in infected water. Farm workers wade in irrigation ditches without boots.
• Larvae of blood flukes burrow into the skin.
• Blood flukes move through the victim's blood vessels, releasing eggs that travel and damage the bladder or intestines.
• They are passed out of the body along with urine or stool.
• If they find their way back to water (which is usually very easy) the process repeats itself.

This cycle is very complicated. The snail (or host) has to be present in order for the disease to spread. Source: CDC

Source: WHO

• Dams, irrigation systems, and other water control projects create new habitats for snails, which serve as hosts for young blood flukes.
• The larger the area that uses irrigation water, the farther the disease can spread.
• When rivers flood—which can be caused by human disruption to nearby ecosystems—snails and the disease spread.
• Fresh water also becomes contaminated with Schistosomiasis eggs when an infected person urinates or defecates into the water.