An Overview of the Biology of the Schistosoma Parasite

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"An Overview of the Biology of the Schistosoma Parasite"
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After Malaria, infection by the parasite known as Schistosoma (S) is considered to be the second most devastating, debilitating, disfiguring and sometimes deadly disease which affects million of people worldwide.  Yet it has been classified as one of the neglected tropical diseases.

The parasite is carried by freshwater snails which are highly prevalent in places such as Asia, Africa and South America. It can be contracted at any age; however children in those areas who play in muddy and contaminated water are most susceptible to catching the disease.

There are three main species of Schistosoma which include S. Mansoni, S. Haemstobium and  S. Japonicum, the larvae of which invades the body by burrowing through four layers of intact skin to gain access to the vascular system.  During migration it transforms into a second larval form, known as the schistosomule, thereafter it travels via the lungs to the hepatic portal vein in the liver where it matures into its adult form.

Once they have reach maturity, depending on the specie, they migrate to various parts of the body to occupy their preferred cites, which can include the liver, the portal vein, bladder, intestines, spleen, rectum, lungs and brain.  They then begin to mate, with the females being capable of producing hundreds of thousands of eggs daily, which is then excreted in the faeces to begin its lifecycle anew.

If the eggs manage to reach fresh water they hatch and begin to swim freely, guided by the light and chemical stimuli in search of their host, the amphibious snail in with to take up residence.  Once inside the snail they begin to propagate asexually producing numerous larvae.

Symptoms vary depending on the specie of the Schistosome parasite and the phase of the infection.  However, the most common symptoms includes itchiness and a rash at the penetration cite, fever, chills, enlargement of the liver, spleen and lymph nodes, abdominal pains, blood stained diarrhoea, frequent and painful and blood stained urination during excretion.

If any of the above symptoms appear, especially in those who have travelled abroad to areas where the infection is prevalent, then the physician should be contacted. He will usually undertake a series of tests to confirm diagnosis, perhaps beginning with a stool test to detect the presence of schistosome eggs in the faeces. This is likely to be followed by a series of blood tests, to check the platelets levels and the levels of the red and white blood cells. He will also check the antigens levels; perhaps undertake a biopsy of the infected tissue and lastly an analyse of the urine.

The infection is treated usually with Praziquantel (Biltricide) which is an Anthelmintic drug, commonly used in the treatment of flatworms and in severe cases where the brain is involved; corticosteroids may be added into the equation. The prognosis is generally good if the symptoms are treated before any significant damage has been done.

The infection can be prevented if swimming in contaminated water is avoided. Water that may be contaminated should be boiled before drinking. The avoidance of water that might contain freshwater snails and lastly bathing in water where the contamination levels are unknown should be avoided.




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