Schistosomiasis or Bilharzia was known to the Egyptians at the time of the pharaohs. Theodor Bilharz, a German pathologist, discovered the causative agent, a parasitic trematode worm, in 1851. There are five different species of Schistosoma implicated in human infections and over 200 million people are infected worldwide.
S. mansoni causes intestinal schistosomiasis it is endemic in South America, the Caribbean, Africa and the Middle East. S. haematobium causes urinary schistosomiasis it is endemic in African and the Middle East. S. japonicum causes intestinal schistosomiasis and is endemic in China, the Philippines and South East Asia. The other two species are comparatively rare causes of intestinal schistosomiasis. S. intercalatum is endemic to the rain forest of Central West Africa. S. mekongi is endemic to Laos, Cambodia and the Mekong delta.
All five species infect humans who enter a contaminated fresh water source. The adult parasites use humans as their definitive hosts. The larval form infects fresh water snails. Free-swimming called cercaria and miracidia infect humans and snails respectively.
Asymptomatic schistosomal infections are common, particularly if the patient has a low parasitic load. An acute form of schistosomiasis, known as Katayama fever, gives rise to a fever, bloody diarrhea and abdominal pain.
Chronic schistosomiasis is the most commonly seen form of the disease. The parasites release eggs into either the intestines or the bladder. Some of the eggs will become lodged in the intestinal or bladder wall instead of passing out from the body. As the eggs are highly immunogenic, the body mounts an attack on the eggs building up granulomatous tissue around the site. Eggs can pass via the portal vein to the liver and hence round the body. The body’s immune response damages organs in which eggs are lodged. The symptoms resulting from this chronic illness will depend on which organs of the body are involved.
Diagnosis of schistosomiasis is by detection of the eggs in either a urine or a stool sample. Schistosome eggs are an elongated oval shape. S .haematobium eggs have a terminal spine while S. mansoni eggs have sub-terminal spine. An adult female schistosome will lay between 200 and 2000 eggs a day.
Not every sample collected from an infected individual will have eggs in sufficient numbers to be detected, particularly in a light infection. Stools are processed with using a parasite concentration technique and the resulting pellet examined microscopically for the characteristic eggs. To maximize the possibility of finding eggs of S. haematobium, a terminal urine taken after exercise is the best sample to examine. Urine samples can be filtered or centrifuged to concentrate the schistosome eggs prior to microscopy.
Testing of urine and stool samples for the presence of blood will aid diagnosis. A full blood count of a patient with schistosomiasis reveals anemia and a marked eosinophilia. Serological tests for antibodies to schistosomes may take up to 22 weeks after initial infection to become positive. Other tests include biopsies of the intestinal wall and x-rays. A chronic infection with S haematobium leads to calcification of the bladder wall. Such calcification is visible on an X-ray.
Treatment of all types of Schistosoma infection is with the drug Praziquantel. This is a very effective and safe drug. Recently laboratory testing has shown some parasites are becoming resistant to Praziquantel. Other drugs used in treating schistosomiasis are Oxamniquine for S. mansoni infections and Metrifonate to treat infections with S. haematobium. Occasionally treating acute schistosomiasis induces a hypersensitivity reaction. In such cases, concurrent treatment with corticosteroid drugs is required