Background. Schistosomiasis is one of a helminth parasitic disease and the third most devastating tropical disease in the world, being a major source of morbidity and mortality for developing countries. This diseases is caused by flukes (trematodes) from the genus Schistosoma. There are five medically important species: Schistosoma haematobium, S. mansoni, S. japonicum, S. mekongi, dan S. intercalatum. Most human schistosomiasis is caused by S. haematobium, S. mansoni, and S. japonicum.
Epidemiology. It is estimated that about 600 million people in 79 countries suffer from schistosomiasis (Bilharziasis). This disease is being a major source of morbidity and mortality for developing countries in Africa, South America, the Caribbean, the Middle East, and Asia. More than 207 million people, 85% of who live in Africa, are infected with schistosomiasis, and an estimated 700 million people are at risk of infection in 76 countries where the disease is considered endemic, as their agricultural work, domestic chores, and recreational activities expose them to infested water. Globally, 200,000 deaths are attributed to schistosomiasis annually. Transmission is interrupted in some countries.
Characteristics. The Schistosomatidae is the one family of trematodes in which the sexes are separate. The adult male is 10 mm long and the female 15 mm but much narrower. When both are mature the female becomes permanently associated with the male which lives within her gynocophoric groove. The female S. japonicum adult worm lays about 500-3,500 eggs daily. The eggs are ovoid, bearing only a minute lateral spine or a small knob posterolaterally. The intermediate hosts are freshwater snails and each species of the worm has a different genus or species of snail host. S. mansoni uses the snail host Biomphalaria spp; S. japonicum has Oncomelania spp and both S. haematobium and S. intercalatum have Bulinus. Although trematodes have a mouth and gut they also absorb food through their tegument and most of it will be amino-acids and sugar associated with blood. Both male and female worms have suckers which are used for attachment. In the female, the birth pore is above the posterior sucker which can penetrate the endothelium cells of the walls of the blood vessels.
Pathophysiology. The clinical course of schistosomiasis usually begins with an allergic reaction to the parasites and their by-products. The schistosomes also cause intestinal, hepatosplenic, pulmonary, urogenital, cerebral and other forms of schistosomiasis. Symptoms may include inflammation, cough, late-afternoon fever, skin eruption (giant urticaria), and swelling and tenderness of the liver.
Treatment. Praziquantel, a prescription medication, is taken for 1-2 days to treat infections caused by all schistosome species.
References:
Ahmed, S.H. Schistosomiasis (Bilharzia) [updated September 20, 2018]. Available from: https://emedicine.medscape.com/article/228392-overview
Dawit A., Ephrem K., S. Nagesh, Solomon G., Fetene D., Jemal A. Medical Parasitology. USAID collaboration with Ethiopia Public Health Training Initiative, The Carter Center, the Ethiopia Ministry of Health, and the Ethiopia Ministry of Education. 2006.
Chernin, J. Parasitology – Lifeline (Modules in life sciences). CRC Press, London: 2000.
