Schistosomiasis Bilharzia or snail fever

What is Schistosomiasis?

Schistosomiasis (also called bilharzia or snail fever) is a parasitic disease caused by certain species of water-borne flatworms or blood flukes.  These parasites are known as schistosomes.

An increasing number of tourists are acquiring the disease with the increased popularity of eco-tourism and travelling off the beaten path.

How do you get Schistosomiasis?

Schistosomiasis is usually contracted by people in developing countries while fishing or farming in contaminated water.  The parasite easily enters through intact skin and matures within organ tissues.

Susceptibility and Resistance

Anyone who travels to an endemic area and is exposed to fresh water sources (usually rivers or lakes) is susceptible to schistosomiasis. Some people who have had shistosomiasis may develop a variable degree of immunity to reinfection, but the duration of any immunity to this illness has not been fully documented.

Incubation Period

The incubation period for Schistosomiasis is 14-42 days.

What are the Symptoms?

Schistosomiasis is mainly a chronic infectious disease.  Many infections do not produce symptoms.  However, acute schistosomiasis may include the following symptoms: diarrhoea, fever, fatigue, abdominal pain, blood in the stool, eosinophilia (increased white blood cell count), hepatosplenomegaly (enlargement of the liver or spleen).  

Late complications of schistosomiasis from chronic infection can include: 

  • S. haematobium can cause urinary symptoms such as dysuria (painful urination), hematuria (blood in the urine), and frequent urination.
  • Obstructive uropathy (condition in which the flow of urine is blocked, injuring the kidneys)  
  • Infertility
  • Portal hypertension (high blood pressure in the portal vein in the abdominal cavity)
  • Liver fibrosis (formation of excess scar tissue in the liver)
  • Colonic polyposis (abnormal growths in the colon)
  • Rarely, S. japonicum can cause seizures and lesions in the central nervous system.
  • There is an increased risk of bladder cancer associated with urinary schistosomiasis.
    The larva of some schistosomes may cause a rash sometimes known as “swimmer’s itch”; however, these schistosomes do not cause schistosomiasis as they do not mature within humans.

Preventative Measures

The best way to reduce the risk of contact with schistosomes is to avoid contact with contaminated water through swimming, bathing, wading, or participating in farming activities in areas where schistosomes are common.


Schistosomiasis is easily treatable with a single dose of the drug Praziquantrel annually. Alternative drugs include oxamniquine to treat S. mansoni, and metrifonate to treat S. haematobium.


Where Does It Commonly Occur?

Different species of schistosomes are found in different parts of the world:

  • S. mansoni is found in Africa, the Eastern Mediterranean, the Caribbean, and South America.
  • S. japonicum is found in China, the Philippines and Sulawesi (Celebes) in Indonesia.
  • S. haematobium occurs in Africa and the Eastern Mediterranean.
  • S. mekongi is found in the Mekong River area of Cambodia and the Lao People’s Democratic Republic.
  • S. intercalatum occurs in parts of western Africa, including Cameroon, Chad, the Democratic Republic of Congo, Gabon, and São Tome.
  • S. malayensis is only found in peninsular Malaysia.
  • Human infection with the bovine parasite, S. mattheei, has been reported from southern Africa.