Over centuries man has been in contact with other living species and while benefitting from it, has acquired some diseases as well. Schistosomiasis is one of them.
Schistosomes (parasites causing schistosomiasis) are blood flukes that affect 200 to 300 million people world wide in tropical climates.
There are 5 species of which 3 are known 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, where infected snails exist are at high risk of acquiring the infection. As larvae mature into adult worms inside the body, they pass from 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 due to the body’s efforts to contain the infection. Severity of the sickness depends on amount of eggs deposited, resistance of the infected person and affected organ in the body.
Initially the person may have a macular papular pruritic rash all over the body, due to allergy produced by the parasite. Involvement of the urinary system will lead to a painless passing of blood in urine. People with bladder involvement are at high risk of developing cancer of the urinary bladder. There may be abdominal pain and fever. Kidneys can 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. This will in turn cause enlargement of liver and spleen and collection of fluid in the peritoneal cavity. 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, the patient becomes very weak and anemic. Lungs are also affected by this parasite. One can 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.
Considering the multiplicity of organs affected by schistosomiasis, one can understand the gravity of the infection. Moreover after treatment, the infection may clear but damage caused to organs persists.
Therefore, early diagnosis and treatment are advocated to prevent organ damage. Schistosomiasis should be considered in some person with features of allergy, urinary tract or liver problems, 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.
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 possible practically on a large scale. People need to be educated widely about this chronic devastating disease and if possible should avoid entering such water bodies. Those who indulge in activities inside 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.
Dr Rachna Pande,
specialist – internal medicine