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Bilharzia (Snail Fever Parasite Infection)

What is bilharzia?

Bilharzia or snail fever (schistomiasis) is an infective disease caused by different species of trematodes (flukes) belonging to the genus Schistosoma. It is also referred to as bilharziasis. After malaria,  bilharziasis is the most common parasitic infection in humans. The disease spreads through contact with contaminated water. Snails act as the intermediary host between Schistosoma parasite and humans. The infection is not life threatening but when left untreated develops into chronic disease with chances of damaging internal organs and even leading to bladder cancer. The disease is highly prevalent (endemic) in tropical and sub-tropical countries due to poor sanitation.

Bilharzia Symptoms

Bilharziasis is mainly a chronic disease but within weeks of infection, acute symptoms (Katayama’s fever) may appear with the following manifestations :

  • Abdominal pain
  • Coughing
  • Diarrhea
  • Fever, weakness
  • Chills
  • Swollen neck glands (lymph nodes)
  • Lump in the abdomen – enlarged liver and spleen (hepatosplenomegaly)
  • Itching of the exposed skin along with rashes (swimmer’s itch)
  • Ulcer on genitals

Chronic infection leads to a different set of symptoms :

  • Anemia(due to blood loss)
  • Malnutrition
  • Weakness (or paralysis) of the limbs :due to brain involvement
  • Bloody diarrhea
  • Bloody vomiting
  • Difficult (painful) urination sometimes with frank bleeding

The most important complications associated with long term bilharzia is bladder cancer and internal organ damage (kidney, liver)

Causes of Bilharzia

Bilharziasis is caused by trematodes (flukes) of the Schistosoma genus (Schistosoma mansoni, S. japonicum, S. haematobium, S. mekongi) The life cycle of the parasite involve two hosts – snails (non-vertebrate) and humans (vertebrate).

Life cycle in snails

Eggs of Schistosoma parasites, from fecal matter of humans, are released into fresh water, hatch and enter the snail’s body. Further maturation of the parasites in the snails’ body leads to the formation of initial primary and later secondary sporocysts. In the liver and pancreas of the snail,  secondary sporocysts produce and release cercariae (human infective form of larva) into fresh water.

Life cycle in humans

Cercariae enter the human body by penetrating the skin, converts into a migrating form and ultimately reach the bloodstream. Via the blood they reach the lungs and finally the liver. It takes almost 8 days after skin penetration to reach the hepatic sinusoids of the liver. The parasites become mature enough at this stage to feed on red blood cells. Some of the parasites reach the blood vessels surrounding the bladder, kidney and ureters. After about 6 to 8 weeks the parasites (both male and female) become sexually active and produce eggs that exit the human body via both urine and stool and reach fresh water due to poor sanitation. Some eggs remain trapped in the body and cause severe allergic reactions which is responsible for long term organ damage. It is not the parasites itself that causes organ damage but the body’s reaction to the parasites.

Who is at risk of bilharzia?

  • Residents of endemic regions Asia, Africa, Middle east and South America (tropical and subtropical region).
  • Poor sanitation.
  • Poor hygiene maintenance.
  • Contact with contaminated (with cercariae) fresh water.

The infection is very often contracted by young children who swim in rivers within these endemic regions.

Treatment for Bilharzia

Rashes due to cercariae penetration require no treatment. Acute conditions are treated with steroids and praziquantel. Praziquantel is the drug of choice but other drugs like (oxamniquine) can be prescribed. Bilharziasis can be controlled by reducing the fresh water dwelling snail population as the infective form in humans (cercariae) develops only in the snails. Snail eradication is just a means of disrupting the life cycle of the Schistosome parasites.


Posted by in Infections and Infestations

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