For centuries, man has been in close contact with other living species in one way or another. Man has benefited in multiple ways by this contact but has also acquired some diseases in turn. Schistosomiasis is one such disease.
Schistosomes (parasites causing schistosomiasis) are blood flukes that affect 200 to 300 million people worldwide in tropical climates.
There are 5 species of which schistosoma mansoni, S. intercalatum and S. haematobium are said to cause disease in Africa.
Infestation occurs by penetration of intact skin by the larval forms of the parasite, released from snails in fresh water bodies. People bathing, swimming or fishing in lakes and ponds, e.t.c., where infected snails exist, are at high risk of acquiring the infection.
As they mature into adult worms inside the body, they pass from portal veins and its small branches to urinary bladder, ureter (tubes connecting kidney to bladder) or intestines, produce and deposit eggs.
Some of these eggs are passed out through the urine or stool. They may reach the water and continue their life cycle, i.e. by infecting snails.
Clinical manifestations develop not due to these eggs which remain in the body but the body’s efforts to contain the infection. Severity of the symptoms depends on amount of eggs deposited, resistance of the infected person and affected organ in the body.
To begin with, the person may have a macular popular pruritic rash all over the body, due to allergy produced by the parasite.
Involvement of the urinary system will lead to a painless haematuria (passing of blood in urine). People with involvement of the bladder are at high risk of developing cancer of the urinary bladder. There may be abdominal pain and fever. Kidneys can also be affected leading to kidney failure.
Due to affection of the portal venous system (that drains impurities from abdominal cavity), there is increase in the tension of portal vein a condition called portal hypertension.
This portal hypertension will in turn cause enlargement of liver and spleen and collection of fluid in the peritoneal cavity (ascites).
Liver cells are damaged by the schistosomes and also by portal hypertension. Slowly, the patient develops liver failure and its complications, can pass into coma and die.
Some species of the worms develop a sucker after entering the liver and begin to feed on the red blood cells.
Due to this and other multiple factors, the patient becomes very weak and anaemic.
Lungs are also not spared by this parasite. One may develop cough due to allergy to the presence of worms in the body. Apart from this, Schistosomes may also damage pulmonary vessels causing pulmonary hypertension and related clinical problems.
Sores may be formed on genital parts that make the person more vulnerable to HIV infection.
Rarely, eggs may be deposited in brain or spinal cord causing paralysis and various neurological problems.
Seeing the multiplicity of organs affected by schistosomiasis, one can understand the gravity of the infection. Moreover after treatment, though the infection may clear, the damage caused to organs persists.
Therefore, early diagnosis and treatment are advocated to prevent organ damage. Schistosomiasis should be remembered while considering parasitic infection in someone, particularly those who live around lakes and ponds.
Diagnosis can be established by simple stool and urine examinations. Serological tests and biopsy of the affected parts is also useful. W.H.O. has established guidelines for community treatment of schistosomiasis in endemic areas to prevent the heavy morbidity and mortality.
This includes giving empirical treatment to people living in such areas, depending on the percentage of children passing blood in urine.
Prevention ideally lies in eliminating the snails which are a natural reservoir of the infection. Chemicals like acrolein, copper sulphate, can be used for this purpose. But this is not practically possible on a large scale.
People need to be widely educated about this chronic devastating disease. People, who live near fresh water bodies and indulge in activities in the water, should seek medical intervention at development of earliest symptom like skin rashes or vesicles.
There is ongoing extensive research for developing an effective vaccine for schistosomiasis. We all hope that it should be successful soon so that many human beings can be protected from it.
The author is a specialist in Internal Medicine