الفهرس 
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Abstract
Schistosomiasis is a disease caused by digenetic trematodes that belong to the family Schistosomatoidae. Five species of Schistosomes are involved in human infection. The three principal agents are S. mansoni and S. japonicum which are responsible for intestinal schistosomiasis and S. haematobium, the aetiologic agent of urinary schistosomiasis. The other two species responsible for intestinal disease though with low frequency are S. intercalatum and S. mekongi.
The disease affects about 240 million people worldwide while an estimated 779 million people (more than 10% of the world population) are at the risk of infection. About 120 million people infected with schistosomiasis are estimated to be symptomatic while about 20 million develop severe disease. The disability-adjusted life years (DALYs) due to schistosomiasis is about 1.7-4.5 million while between 150,000 to 280,000 people are known to die as a consequence of the disease per year. Africa accounts for 85% of the disease burden. Although, schistosomiasis is a rural focal disease typically associated with farmers and fishermen in the tropics, it is increasingly been reported among Europeans with a history of travel to endemic areas in Africa and Asia. It is transmitted by snails found in cercariae infested fresh water streams. Snails belonging to the species Bulinus, Biomphalaria and Onchomelania are the vectors of S. haematobium, S. mansoni and S. japonicum respectively. Egypt is a cradle of civilization, but has been plagued by schistosomiasis since at least the Middle Kingdom period (1,500 BC). It was traditionally the most important public health problem.
A person can become infected by prolonged contact (like bathing or swimming) with fresh water containing free swimming cercariae, the infective stage of the parasite that then enters the subcutaneous tissues, then the blood stream, migrates to the lungs, then to the liver, and finally to the mesenteric and perivesical venous plexuses. The parasite is excreted from the body via urine and faeces into fresh water and the miracidia eventually infects its intermediate hosts, the fresh water snails, where they develop into cercariae and the unfortunate cycle restarts again.
The main effect of the parasite is chronic granulomatous injury in response to the eggs that are shed. The first sign of infection can be a reactive dermatitis syndrome with pruritis, inflammation, and the presence of a small erythematous macule, at the site of entry of the cercariae in the first few minutes after invasion, which may disappear within a few hours. Up to two weeks later there may be a small papule at the same site, also associated with pruritis. Approximately two months after infection the person can present with katayama fever, lasting for up to two weeks or several months, with temperatures reaching as high as 40°C with rigors, diarrhea, lethargy, myalgia, headache, nausea, and vomiting. Urinary schistosomiasis is caused by S. haematobium and deposition of eggs in the bladder and ureters. The subsequent granulomatous inflammation causes nodules, polypoid lesions, and ulcerations in the lumens of the ureter and bladder, which in turn causes urinary frequency, dysuria, and end stream haematuria. chronic renal failure and carcinoma of the bladder occur with increased frequency in S. haematobium infected patients. When schistosomiasis affects the intestines, the patient can present with colicky abdominal pain, bloody diarrhea, and hepatosplenomegaly. In the lungs the effects can be pulmonary hypertension and corpulmonale. In rare cases it can infect the brain causing seizures. The diagnosis strongly depends on the physician’s awareness of this as a possible differential diagnosis, especially if there is a history of bathing in fresh water in endemic areas of Asia, South Africa, and Africa, a history of a pruritic reaction on an exposed area of skin after bathing, or an unexplained febrile illness several weeks later. A definitive diagnosis can only be made with evidence of viable eggs in the urine, stool, or biopsy specimens. A urine sample best taken at midday after exercise, when most eggs are being shed, is ideal and microscopy often reveals eggs and parasites. In some cases a renal ultrasound, cystoscopy, and biopsy of the bladder mucosa is recommended if the urine microscopy is not conclusive or if the extent of infection and damage to the urinary tract needs further investigation. Identification of the schistosoma eggs in stool with a thick smear method of Kato is very sensitive. Methods of immunoassay like ELISA and RIA are sensitive but not specific and can be considered in early schistosomiasis when there is a strong suspicion. In some cases the serological immunofluorescence antibody test for the presence of specific antibodies has been found to be a sensitive marker of acute and chronic infection.