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Schistosomiasis Penny Tompkins
VT216
General Info
Schistosomiasis, is a parasitic infection caused by trematodes, also known as flatworms or flukes, from the genus Schistosoma.
After malaria, schistosomiasis is the second most prevalent tropical disease in the world.
The Recent World Health Organization (WHO) reported an estimate of 500-600 million people in 74 tropical and subtropical countries are at risk for schistosomiasis.
More than 200 million people in these countries are infected. Of these, 120 million are symptomatic, with 20 million having severe clinical disease.
Types
There are five species of flatworms that cause schistosomiasis, and each causes a different clinical presentation of the disease.
Schistosomiasis may localize in different parts of the body, and its localization determines its particular clinical profile.
Schistosoma mansoni and Schistosoma intercalatum cause intestinal schistosomiasis
Schistosoma haematobium causes urinary schistosomiasis
Schistosoma japonicum and Schistosoma mekongi cause the Asian form of intestinal schistosomiasis
SchistosomiasisClassification and
external resources
Skin vesicles created by the penetration of
Schistosoma. Source: CDC
Transmission
Infection occurs when your skin comes in contact with contaminated freshwater where certain types of snails that carry schistosomes are living.
The eggs hatch, and if certain types of snails are present in the water, the parasites grow and develop inside the snails.
The parasite leaves the snail and enters the water where it can survive for about 48 hours. Schistosoma parasites can penetrate the skin of persons who are wading, swimming, bathing, or washing in contaminated water.
Within several weeks, worms grow inside the blood vessels of the body and produce eggs. Some of these eggs travel to the bladder or intestines and are passed into the urine or stool.
Clinical Signs
Abdominal pain Cough Diarrhea Eosinophilia - extremely high eosinophil
granulocyte count. Fever Fatigue Hepatosplenomegaly - the enlargement
of both the liver and the spleen.
Clinical Signs Cont…
Colonic polyposis with bloody diarrhea
Portal hypertension with hematemesis and splenomegaly
Cystitis and ureteritis with hematuria, which can progress to bladder cancer;
Pulmonary hypertension
Diagnosis
Diagnosis is made by finding the characteristic eggs in stool or urine. Because eggs may be excreted intermittently, several specimens should be examined.
Occasionally, a rectal or bladder biopsy may be necessary.
Serology is the most sensitive diagnostic tool and is particularly useful for detecting light infections.
SC
HIS
TO
SO
MIA
SIS An embryonated egg of Schistosoma bovis as seen in a fecal sample from a
cow. Courtesy of Professor M. G. Taylor
Treatment
Safe and effective drugs are available for the treatment of schistosomiasis. Praziquantel (25 mg/kg) is highly effective, although 2 treatments 3-5 wk apart may be required.
Reduction of transmission is accomplished by providing safe water supplies and proper sanitation facilities.
Much of the focus of current schistosomiasis control strategies is to minimize the morbidity caused by the infection through mass treatment of at risk populations with praziquantel. This approach also leads to the reduction of egg output and transmission.
Prevention Avoid swimming or wading in
freshwater when you are in countries where schistosomiasis occurs. Swimming in the ocean and in chlorinated swimming pools is generally thought to be safe.
Bath water should be heated for 5 minutes at 150°F. Water held in a storage tank for at least 48 hours should be safe for showering.
Drink safe water. Because there is no way to make sure that water coming directly from canals, lakes, rivers, streams or springs is safe, you should either boil water for 1 minute or filter water before drinking it.
Boiling water for at least 1 minute will kill any harmful parasites, bacteria, or viruses present.
References
Bierman WF, Wetsteyn JC, van Gool T. Presentation and diagnosis of imported schistosomiasis: relevance of eosinophilia, microscopy for ova, and serology. J Travel Med. 2005 Jan-Feb;12(1):9-13.
Jordan P. Schistosomiasis. The St. Lucia Project. New York: Cambridge University Press
Ali El-Garem, A. (1998). "Schistosomiasis." Digestion 59:589–605. Bica, I.; Hamer, D. H.; and Stadecker, M. J. (2000). "Hepatic
Schistosomiasis." Infectious Disease Clinics of North America 14(3):583–604.
Dunne, D. W.; Hagan, P.; and Abath, F. G. C. (1995). "Prospects for Immunological Control of Schistosomiasis." Lancet 345:1488–1492.
Elliot, D. E. (1996). "Schistosomiasis, Pathophysiology, Diagnosis and Treatment." Gastroenterology Clinics of North America 25(3):599–625.
