Schistosomiasis

Background

This infection is a worldwide public health problem. It is a parasitic infection caused by several species of Schistosomatoidea. Fresh water becomes contaminated when infected people urinate or defecate in the water, releasing Schistosoma eggs. Fresh water snails harboring the parasite come into contact with your skin. 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. After penetrating the skin, 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.

Within days after becoming infected, a rash or itchy skin may develop. Fever, chills, cough, and muscle aches can begin within 1-2 months of infection. Most people have no symptoms at this early phase of infection. Eggs travel to the liver or pass into the intestine or bladder but eggs may travel to virtually any organ in the body. The symptoms of schistosomiasis are caused by the body's reaction to the eggs produced by worms, and not by the worms themselves.

OUTLINE

Epidemiology

Disease Associations

Pathogenesis

Laboratory/Radiologic/
Other Diagnostic Testing

Gross Appearance
and Clinical Variants

Histopathological Features
and Variants

Special Stains/
Immunohistochemistry/
Electron Microscopy

Differential Diagnosis

Prognosis

Treatment

Commonly Used Terms

Internet Links

EPIDEMIOLOGY CHARACTERISTICS

SYNONYMS Bilharzia

GEOGRAPHY

Africa
Southern Africa, sub-Saharan Africa, Lake Malawi, the Nile River valley in Egypt

South America
Brazil, Suriname, Venezuela

Caribbean
Antigua, Dominican Republic, Guadeloupe, Martinique, Montserrat, Saint Lucia (risk is low)

The Middle East
Iran, Iraq, Saudi Arabia, Syrian Arab Republic, Yemen, Southern China

Southeast Asia
Philippines, Laos, Cambodia, Japan, central Indonesia, Mekong delta

PATHOGENESIS CHARACTERIZATION

Schistosomiasis species-Life cycle
Adult worms in humans reside in the mesenteric venules in various locations, fairly specific for each species

Species can occupy several locations and are capable of moving between locations

Females (size 7 to 20 mm; males slightly smaller) deposit eggs in the small venules of the portal and perivesical systems

Eggs are moved progressively toward the lumen of the intestine (S. mansoni and S. japonicum) and of the bladder and ureters (S. haematobium), and are eliminated with feces or urine, respectively

Under optimal conditions the eggs hatch and release miracidia, which swim and penetrate specific snail intermediate hosts

The stages in the snail include 2 generations of sporocysts and the production of cercariae

Upon release from the snail, the infective cercariae swim, penetrate the skin of the human host, and migrate through several tissues and stages to their residence in the veins

Schistosoma mansoni
South America and the Caribbean, Africa, and the Middle East
more often in the superior mesenteric veins

S. haematobium

Africa and the Middle East

venus plexus of bladder, but it can also be found in the rectal venules.

S. japonicum

Far East
inferior mesenteric veins

Schistosoma mekongi
Southeast Asia

S. intercalatum
Central West Africa

LABORATORY/
RADIOLOGIC CHARACTERIZATION

Laboratory Markers

Microscopic examination of urine and feces

Most practical method for diagnosis-depends upon type of species interested in identifying

Stool examination: S. mansoni or S. japonicum
Urine examination: S. haematobium

Eggs can be present in the stool in infections with all Schistosoma species

Simple smear (1 to 2 mg of fecal material)

Since eggs may be passed intermittently or in small amounts, their detection will be enhanced by repeated examinations and/or concentration procedures (such as the formalin - ethyl acetate technique)

Egg output can be quantified by using the Kato-Katz technique (20 to 50 mg of fecal material) or the Ritchie technique

Eggs can be found in the urine in infections with S. haematobium (recommended time for collection: between noon and 3 PM) and with S. japonicum

Detection will be enhanced by centrifugation and examination of the sediment

Quantification is possible by using filtration through a Nucleopore� membrane of a standard volume of urine followed by egg counts on the membrane

Tissue biopsy (rectal biopsy for all species and biopsy of the bladder for S. haematobium) may demonstrate eggs when stool or urine examinations are negative

GROSS APPEARANCE/
CLINICAL VARIANTS CHARACTERIZATION

General

VARIANTS

Swimmer's itch, also called cercarial dermatitis

Skin rash caused by an allergic reaction to infection with schistosomal parasites of birds and mammals

Microscopic parasites are released from infected snails to swim in fresh and salt water, such as lakes, ponds, and oceans used for swimming and wading

Worldwide

Generally occurs during summer months

Acute schistosomiasis (Katayama's fever)

May occur weeks after the initial infection, especially by S. mansoni and S. japonicum

Fever, cough, abdominal pain, diarrhea, hepatospenomegaly, and eosinophilia with occasionally central nervous system lesions

Chronic infection

Granulomatous reactions and fibrosis in the affected organs:

Colonic polyposis with bloody diarrhea
(Schistosoma mansoni mostly)

Portal hypertension with hematemesis and splenomegaly
(S. mansoni, S. japonicum, S. mansoni)

Cystitis and ureteritis (S. haematobium) with hematuria, which can progress to bladder cancer

Pulmonary hypertension (S. mansoni, S. japonicum, more rarely S. haematobium)

Glomerulonephritis

Central nervous system lesions.

PROGNOSIS AND TREATMENT CHARACTERIZATION

Treatment

Preventive

Avoid swimming or wading in fresh water when you are in countries in which schistosomiasis occurs

Drink safe water by boiling water for at least 1 minute-Iodine treatment alone will not guarantee that all parasites are killed

Vigorous towel drying after an accidental, very brief water exposure may help to prevent the Schistosoma parasite from penetrating the skin

Medical

Henry JB. Clinical Diagnosis and Management by Laboratory Methods. Twentieth Edition. WB Saunders. 2001.

Commonly Used Terms

Basic Principles of Disease
Learn the basic disease classifications of cancers, infections, and inflammation

Commonly Used Terms
This is a glossary of terms often found in a pathology report.

Diagnostic Process
Learn how a pathologist makes a diagnosis using a microscope

Surgical Pathology Report
Examine an actual biopsy report to understand what each section means

Special Stains
Understand the tools the pathologist utilizes to aid in the diagnosis

How Accurate is My Report?
Pathologists actively oversee every area of the laboratory to ensure your report is accurate

Got Path?
Recent teaching cases and lectures presented in conferences

Internet Links

Pathologists Who Make A Difference
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Microscopic Photo

Last Updated 1/5/2004

Epidemiology
Disease Associations
Pathogenesis
Laboratory/Radiologic/ Other Diagnostic Testing
Gross Appearance and Clinical Variants
Histopathological Features and Variants
Special Stains/ Immunohistochemistry/ Electron Microscopy
Differential Diagnosis
Prognosis
Treatment
Commonly Used Terms
Internet Links

EPIDEMIOLOGY	CHARACTERISTICS
SYNONYMS	Bilharzia
GEOGRAPHY
Africa	Southern Africa, sub-Saharan Africa, Lake Malawi, the Nile River valley in Egypt
South America	Brazil, Suriname, Venezuela
Caribbean	Antigua, Dominican Republic, Guadeloupe, Martinique, Montserrat, Saint Lucia (risk is low)
The Middle East	Iran, Iraq, Saudi Arabia, Syrian Arab Republic, Yemen, Southern China
Southeast Asia	Philippines, Laos, Cambodia, Japan, central Indonesia, Mekong delta

PATHOGENESIS	CHARACTERIZATION
Schistosomiasis species-Life cycle	Adult worms in humans reside in the mesenteric venules in various locations, fairly specific for each species Species can occupy several locations and are capable of moving between locations Females (size 7 to 20 mm; males slightly smaller) deposit eggs in the small venules of the portal and perivesical systems Eggs are moved progressively toward the lumen of the intestine (S. mansoni and S. japonicum) and of the bladder and ureters (S. haematobium), and are eliminated with feces or urine, respectively Under optimal conditions the eggs hatch and release miracidia, which swim and penetrate specific snail intermediate hosts The stages in the snail include 2 generations of sporocysts and the production of cercariae Upon release from the snail, the infective cercariae swim, penetrate the skin of the human host, and migrate through several tissues and stages to their residence in the veins
Schistosoma mansoni	South America and the Caribbean, Africa, and the Middle East more often in the superior mesenteric veins
S. haematobium	Africa and the Middle East venus plexus of bladder, but it can also be found in the rectal venules.
S. japonicum	Far East inferior mesenteric veins
Schistosoma mekongi	Southeast Asia
S. intercalatum	Central West Africa

LABORATORY/ RADIOLOGIC	CHARACTERIZATION
Laboratory Markers
Microscopic examination of urine and feces	Most practical method for diagnosis-depends upon type of species interested in identifying Stool examination: S. mansoni or S. japonicum Urine examination: S. haematobium Eggs can be present in the stool in infections with all Schistosoma species Simple smear (1 to 2 mg of fecal material) Since eggs may be passed intermittently or in small amounts, their detection will be enhanced by repeated examinations and/or concentration procedures (such as the formalin - ethyl acetate technique)
	Egg output can be quantified by using the Kato-Katz technique (20 to 50 mg of fecal material) or the Ritchie technique Eggs can be found in the urine in infections with S. haematobium (recommended time for collection: between noon and 3 PM) and with S. japonicum Detection will be enhanced by centrifugation and examination of the sediment Quantification is possible by using filtration through a Nucleopore� membrane of a standard volume of urine followed by egg counts on the membrane Tissue biopsy (rectal biopsy for all species and biopsy of the bladder for S. haematobium) may demonstrate eggs when stool or urine examinations are negative

GROSS APPEARANCE/ CLINICAL VARIANTS	CHARACTERIZATION
General
VARIANTS
Swimmer's itch, also called cercarial dermatitis	Skin rash caused by an allergic reaction to infection with schistosomal parasites of birds and mammals Microscopic parasites are released from infected snails to swim in fresh and salt water, such as lakes, ponds, and oceans used for swimming and wading Worldwide Generally occurs during summer months
Acute schistosomiasis (Katayama's fever)	May occur weeks after the initial infection, especially by S. mansoni and S. japonicum Fever, cough, abdominal pain, diarrhea, hepatospenomegaly, and eosinophilia with occasionally central nervous system lesions
Chronic infection	Granulomatous reactions and fibrosis in the affected organs: Colonic polyposis with bloody diarrhea (Schistosoma mansoni mostly) Portal hypertension with hematemesis and splenomegaly (S. mansoni, S. japonicum, S. mansoni) Cystitis and ureteritis (S. haematobium) with hematuria, which can progress to bladder cancer Pulmonary hypertension (S. mansoni, S. japonicum, more rarely S. haematobium) Glomerulonephritis Central nervous system lesions.

PROGNOSIS AND TREATMENT	CHARACTERIZATION
Treatment
Preventive	Avoid swimming or wading in fresh water when you are in countries in which schistosomiasis occurs Drink safe water by boiling water for at least 1 minute-Iodine treatment alone will not guarantee that all parasites are killed Vigorous towel drying after an accidental, very brief water exposure may help to prevent the Schistosoma parasite from penetrating the skin
Medical