Schistosomiasis overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]
Overview
Schistosomiasis is an infection acquired through contact with fresh water infested with the infectious larval form of Schistosoma flat worms (trematodes). Although schistosomiasis is a tropical disease, travelers, students, immigrants, veterans, and tourists who previously lived in or visited regions where schistosomiasis is endemic, present worldwide. Early disease is usually asymptomatic, unless Katayama fever, an acute immune complex disease occurs. Late disease is symptomatic and includes hepatosplenic schistosomiasis (pre sinusoidal portal hypertension), urinary and urogenital schistosomiasis (urinary obstruction, genital symptoms), schistosomal glomerulopathy (chronic immune complex deposition in the kidney), and ectopic disease in areas such as the lungs and central nervous system (CNS). Diagnostic methods include visualization of Schistosoma eggs in formed stool, urine, and crushed biopsy tissues; serologic assays; and urinary antigen testing. Scarring patterns characteristic of hepatosplenic and urogenital disease may be seen on ultrasonography. Praziquantel is first-line treatment.
Historical Perspective
Schistosomiasis is known as bilharzia or bilharziosis in many countries, after German physician Theodor Bilharz, who first described the cause of urinary schistosomiasis in 1851. The first doctor who described the entire disease cycle was Pirajá da Silva in 1908. It was a common cause of death for ancient Egyptians in the Greco-Roman period.
Classification
Schistosomiasis may be classified based on the organ involvement into intestinal and urogenital schistosomiasis.
Pathophysiology
The pathogenesis of acute human schistosomiasis is mainly related to egg deposition and liberation of antigens of adult worms and eggs. A strong inflammatory response characterized by high levels of pro-inflammatory cytokines, such as interleukins 1, 6, tumor necrosis factor-α, and by circulating immune complexes participates in the pathogenesis of the acute phase of the disease. Schistosomes have a typical trematode vertebrate-invertebrate lifecycle, with humans being the definitive host. The life cycles of all five human schistosomes are broadly similar. Infection can occur by penetration of the human skin by cercaria or following the handling of contaminated soil. Cercaria gets transformed into migrating schistosomulum stage in the skin. The incubation period for acute schistosomiasis is usually 14-84 days. Both the early and late manifestations of schistosomiasis are immunologically mediated. The major pathology of infection occurs with chronic schistosomiasis in which retention of eggs in the host tissues is associated with chronic granulomatous injury.
Causes
Schistosomiasis is caused by Schistosoma. The major intestinal schistosomes include S.japonicum, S.mekongi, S.mansoni, S.intercalatum. The major urogenital schistosome is S.haematobium.
Differentiating Schistosomiasis from Other Diseases
Schistosomiasis must be differentiated from tapeworm infections that cause abdominal pain, fever, chills, cough, and muscle aches such as like diphyllobothriasis, hymenolepiasis, and taeniasis.
Epidemiology and Demographics
More than 600 million persons are exposed to Schistosoma parasites, 200 million persons are infected, and 20 million symptomatic cases of schistosomiasis are reported worldwide. All age groups are vulnerable to Schistosoma infection, but school-aged children and adolescents living in endemic areas tend to have the highest intensity of disease. There is no racial predilection to schistosomiasis. Schistosomiasis affects men and women equally.
Risk Factors
The most potent risk factor in the development of schistosomiasis is skin exposure to contaminated fresh water (wading, swimming, washing, or working in fresh water that is infested with cercariae). Other risk factors include travel to endemic areas.
Screening
Routine screening of travelers for schistosomiasis is not recommended. Screening is recommended only to guide mass public health treatment programs to targeted villages in endemic areas.
Natural History, Complications and Prognosis
If left untreated, most of the patients with schistosomiasis may progress to develop ulceration or cancer of the bladder, liver or kidney failure. Common complications of schistosomiasis include hematuria, malnutrition, intestinal polyps, hydronephrosis, glomerulonephritis, bladder polyps, bladder cancer, infertility, ectopic pregnancy, renal failure, and cor-pulmonale. Depending on the extent of the disease progression at the time of diagnosis, the prognosis of schistosomiasis may vary. However, the prognosis is generally regarded as good with treatment.
Diagnosis
History and Symptoms
The majority of patients with schistosomiasis in early phase are asymptomatic, unless katayama fever, an acute immune complex disease, occurs. Late Schistosomiasis is symptomatic and includes hepatosplenic schistosomiasis (pre sinusoidal portal hypertension), urinary and urogenital schistosomiasis (urinary obstruction, genital symptoms), schistosomal glomerulopathy (chronic immune complex deposition in the kidney), and ectopic disease in areas such as the lungs and central nervous system (CNS).
Physical Examination
Common physical examination findings of schistosomiasis include generalized lymphadenopathy, hepatosplenomegaly, rash, fever, right upper quadrant tenderness, urticaria, bloody stool.
Laboratory Findings
Methods for diagnosing schistosomiasis include visualization of Schistosoma eggs in formed stool, urine, and crushed biopsy tissues; serologic assays; and urinary antigen testing. Laboratory findings consistent with the diagnosis of schistosomiasis include detection of circulating antibodies to schistosomes and schistosomal antigen in serum.
Electrocardiogram
There are no ECG findings associated with schistosomiasis.
X-ray
A chest x-ray may be helpful in the diagnosis of pulmonary schistosomiasis. Findings on a chest x-ray suggestive pulmonary schistosomiasis include patchy infiltrates, signs of increased vascular and interstitial marking and mild lymphadenopathy.
CT scan
Head, abdomen and lung CT may be helpful in the diagnosis of schistosomiasis. Findings include nodular and ring-enhancing lesions with surrounding edema in neuro-schistosomiasis, calcified capsules in hepatosplenic schistosomiasis and interstitial fibrosis in pulmonary schistosomiasis.
MRI
There are no MRI findings associated with schistosomiasis.
Ultrasound
Ultrasound may be helpful in the diagnosis of urogenital and intestinal schistosomiasis. Findings on an ultrasound suggestive of urogenital schistosomiasis include scarring patterns of bladder wall. Findings on an ultrasound suggestive of intestinal schistosomiasis (periportal fibrosis) include multiple echogenic areas, each with central echo lucency.
Other imaging findings
There are no other imaging findings associated with schistosomiasis.
Other diagnostic studies
There are no other diagnostic studies associated with schistosomiasis.
Treatment
Medical Therapy
The mainstay of treatment for schistosomiasis is pharmacotherapy. Praziquantel is the drug of choice in treating schistosomiasis. Corticosteroids should be administered in addition to praziquantel in patients with symptoms due to neuro-schistosomiasis and patients with severe katayama fever. The goals of treatment of schistosomiasis are to eradicate the helminth and correct any sequelae of infection. While praziquantel is safe and highly effective in curing an infected patient, it does not prevent re-infection by cercariae and is thus not an optimum treatment for people living in endemic areas.
Surgery
Surgical intervention is not usually recommended for the management of schistosomiasis but may be indicated to treat associated complications. Surgery does not treat or eradicate Schistosoma infection. Surgical options include portacaval shunting, ligations of esophageal varices, and surgical removal of genitourinary granulomatous masses.
Primary Prevention
Effective measures for the primary prevention of schistosomiasis include avoiding swimming or wading in freshwater that may be infested with cercariae, water used for bathing should be brought to a rolling boil for 1 minute to kill any cercariae, and then cooled before bathing to avoid scalding. Vigorous towel drying after an accidental water exposure may help to prevent the Schistosoma parasite from penetrating the skin.
Secondary Prevention
Secondary preventive measures of schistosomiasis are similar to primary preventive measures.