Schistosomiasis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]

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.

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.

Schistosomiasis may be classified based on the organ involvement into intestinal and urogenital schistosomiasis.

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.

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.

Schistosomiasis must be differentiated from tapeworm infections that cause abdominal pain, fever, chills, cough, and muscle aches such as like diphyllobothriasis, hymenolepiasis, and taeniasis.

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.

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.

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.

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.

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).

Common physical examination findings of schistosomiasis include generalized lymphadenopathy, hepatosplenomegaly, rash, fever, right upper quadrant tenderness, urticaria, bloody stool.

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.

There are no ECG findings associated with schistosomiasis.

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.

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.

There are no MRI findings associated with schistosomiasis.

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.

There are no other imaging findings associated with schistosomiasis.

There are no other diagnostic studies associated with schistosomiasis.

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.

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.

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 preventive measures of schistosomiasis are similar to primary preventive measures.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]

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.

• In 1847, Japanese Doctor Y. Fujii described “Katayama fever” as a manifestation of acute schistosomiasis.
• 1851, Dr.Theodore Billharz, working in Egypt, identified the worms responsible for Schistosomiasis.^[1]
• 1904, S. japonicum was identified in a housecat.
• In 1908, Dr Pirajá da Silva described the entire disease cycle for the first time.
• 1915, the snail was identified as an intermediate host for Schistosomiasis.^[2]

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]

Schistosomiasis may be classified into intestinal and urogenital schistosomiasis based on the organ involvement.

Schistosomiasis may be classified into intestinal and urogenital schistosomiasis based on the organ involvement.^[1]

Organ involved	Species	Geographical distribution
Intestinal schistosomiasis	Schistosoma mansoni	Africa, Middle East, Caribbean, Brazil, Venezuela and Suriname
	Schistosoma japonicum	China, Indonesia, Philippines
	Schistosoma mekongi	Several districts of Cambodia and the Lao People’s Democratic Republic
	Schistosoma guineensis Schistosoma intercalatum	Rain forest areas of central Africa
Urogenital schistosomiasis	Schistosoma haematobium	Africa, Middle East, Corsica (France)

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]

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 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.

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.^[1][2]

• Schistosomal eggs are released into the environment from infected individuals.
• The schistosomal eggs hatch on contact with fresh water to release the free-swimming miracidium.
• Miracidia infect fresh-water snails by penetrating the snail’s foot.
• After infection, the miracidium transforms into a primary sporocyst.
• Germ cells within the primary sporocyst will then begin dividing to produce secondary sporocysts, which migrate to the snail’s hepatopancreas.
• Once at the hepatopancreas, germ cells within the secondary sporocyst begin to divide producing thousands of new parasites, known as cercariae, which are the larvae capable of infecting mammals.
• Cercariae emerge daily from the snail host in a circadian rhythm, dependent on ambient temperature and light.
• Young cercariae are highly motile, alternating between vigorous upward movement and sinking to maintain their position in the water.
• Cercarial activity is particularly stimulated by water turbulence, by shadows and by chemicals found on human skin.

• Penetration of the human skin occurs after the cercaria have attached to and explored the skin.
• The parasite secretes enzymes that break down the skin’s protein to enable penetration of the cercarial head through the skin.
• As the cercaria penetrates the skin it transforms into a migrating schistosomulum stage.
• The newly transformed schistosomulum may remain inside the skin for 2 days before locating a post-capillary venule.
• The schistosomulum travels from the skin to the lungs where it undergoes further developmental changes necessary for subsequent migration to the liver.
• Eight to ten days after penetration of the skin, the parasite migrates to the liver sinusoids.
• The nearly-mature worms pair, with the longer female worm residing in the gynaecophoric channel of the male.
• S. haematobium schistosomula ultimately migrates from the liver to the perivesical venous plexus of the bladder, ureters, and kidneys through the hemorrhoidal plexus.
• Parasites reach maturity in six to eight weeks, at which time they begin to produce eggs.
• S. haematobium eggs pass through the ureteral or bladder wall and into the urine.
• Only mature eggs are capable of crossing into the digestive tract, possibly through the release of proteolytic enzymes, but also as a function of host immune response, which fosters local tissue ulceration.
• Up to half the eggs released by the worm pairs become trapped in the mesenteric veins, or will be washed back into the liver, where they will become lodged.
• Trapped eggs mature normally, secreting antigens that elicit a vigorous immune response.
• The eggs themselves do not damage the body rather it is the cellular infiltration resultant from the immune response that causes the pathology classically associated with schistosomiasis.

Infection can occur by:

• Penetration of the human skin by cercaria
• Handling of contaminated soil
• Consumption of contaminated water or food sources (e.g, unwashed garden vegetables)

• Cercaria gets transformed into migrating schistosomulum stage in the skin.
• Migrating schistosomulum are transported via the blood stream to respective organ system.

• The incubation period for acute schistosomiasis is usually 14-84 days.

• Cercaria are the infective stage of schistosomiasis to humans.

• Miracidium is diagnostic for schistosomiasis.

• The pathogenesis of acute human schistosomiasis is related to egg deposition and liberation of antigens of adult worms and eggs.^[3]
• A strong inflammatory response characterized by high levels of pro-inflammatory cytokines, such as interleukins 1 and 6 and tumor necrosis factor-α, and by circulating immune complexes participates in the pathogenesis of the acute phase of the disease.

• Both the early and late manifestations of schistosomiasis are immunologically mediated.^[4][5]
• The major pathology of infection occurs with chronic schistosomiasis.
• Eggs may be trapped at sites of deposition (urinary bladder, ureters, intestine) or be carried by the bloodstream to other organs, most commonly the liver and less often the lungs and central nervous system.
• The host response to these eggs involves local as well as systemic manifestations.
• The cell-mediated immune response leads to granulomas composed of lymphocytes, macrophages, and eosinophils that surround the trapped eggs and add significantly to the degree of tissue destruction.
• Granuloma formation in the bladder wall and at the ureterovesical junction results in the major disease manifestations of schistosomiasis haematobia (hematuria, dysuria, and obstructive uropathy).
• Intestinal, as well as hepatic granulomas, underlie the pathologic sequelae of the other schistosome infections( ulcerations and fibrosis of intestinal wall, hepatosplenomegaly, and portal hypertension) due to pre-sinusoidal obstruction of blood flow.
• Anti-schistosome inflammation increases circulating levels of proinflammatory cytokines.
• These responses are associated with hepcidin-mediated inhibition of iron uptake and use, leading to anemia of chronic inflammation.
• Schistosomiasis-related undernutrition may be the result of similar pathways of chronic inflammation.
• Acquired partial protective immunity against schistosomiasis has been demonstrated in some animal species and may occur in humans.

• Recurrent Salmonella infections can occur in patients with schistosomiasis. Salmonella bacteria live in symbiosis within the parasite’s integument, allowing them to evade eradication by many antibiotics.^[6]
• Chloramphenicol-sensitive Salmonella entericaserovar Typhi has been shown to be refractory to chloramphenicol therapy in patients coinfected with Schistosoma.
• Patients coinfected with hepatitis C virus and Schistosoma have increased progression of liver fibrosis compared to patients with hepatitis C alone.^[7]
• Urogenital schistosomiasis is a co-factor in the spread and progression of human immunodeficiency virus (HIV) infection and other sexually transmitted infections, especially in women, and also is associated with female infertility.^[8]

• Adult worms are about 10 mm long

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

• Schistosoma mansoni
• Schistosoma intercalatum
• Schistosoma haematobium
• Schistosoma japonicum
• Schistosoma mekongi

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Furqan M M. M.B.B.S[2]

Schistosomiasis must be differentiated from tapeworm infections that cause abdominal pain, fever, chills, cough, and muscle aches such as like diphyllobothriasis, hymenolepiasis, and taeniasis.

Schistosomiasis must be differentiated from tapeworm infections that cause abdominal pain, fever, chills, cough, and muscle aches such as diphyllobothriasis, hymenolepiasis, and taeniasis.The table below summarizes the findings that differentiate schistosomiasis from other conditions that may cause abdominal pain, fever, chills, cough, and muscle aches.^[1]

Infections	Common causative threadworms	Suggestive findings	Diagnostic approach	Treatment
Schistosomiasis	(Schistosoma japonicum,Schistosoma mansoni and Schistosoma haematobium)	Abdominal pain Cough Diarrhea Fever Fatigue	Stool examination for the eggs USG liver	Praziquantel
Taeniasis	Taenia solium and Taenia saginata	Nausea Vomiting Epigastric pain	Stool examination for the eggs and proglottids Brain CT scan or Biopsy (for cysticercosis)	Praziquantel
Diphyllobothriasis	Diphyllobothrium latum	Epigastric pain Diarrhea Fatigue Nausea Vomiting Numbness Tingling	Stool examination for the eggs and adults PCR	Praziquantel
Hymenolepiasis	Hymenolepis nana	Nausea Vomiting Abdominal pain Dizziness	Stool examination for the eggs and proglottids	Praziquantel

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]

The prevalence of schistosomiasis is approximately 268 per 100,000 individuals worldwide. 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.

• The prevalence of schistosomiasis is approximately 268 per 100,000 individuals worldwide.

• Patients of all age groups may develop schistosomiasis, but school-aged children and adolescents living in endemic areas tend to have the highest intensity of disease.^[1]

• There is no racial predilection to schistosomiasis.

• Schistosomiasis affects men and women equally.

• The disease is found in tropical countries in Africa, Caribbean, Eastern South America, Southeast Asia and in Middle East.
• Schistosoma mansoni is found in parts of South America and Caribbean, Africa, and Middle East.
• S. haematobium is found in Africa and Middle East; and S. japonicum in Far East.
• S. mekongi and S. intercalatum are found locally in Southeast Asia and Central West Africa, respectively.
• Schistosomiasis is endemic in 74-76 developing countries, infecting more than 207 million people, 85% of whom live in Africa.^[2]

Organ involved	Species	Geographical distribution
Intestinal schistosomiasis	Schistosoma mansoni	Africa, Middle East, Caribbean, Brazil, Venezuela and Suriname
	Schistosoma japonicum	China, Indonesia, Philippines
	Schistosoma mekongi	Several districts of Cambodia and the Lao People’s Democratic Republic
	Schistosoma guineensis Schistosoma intercalatum	Rain forest areas of Central Africa
Urogenital schistosomiasis	Schistosoma haematobium	Africa, Middle East, Corsica (France)

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]

The most potent risk factor in the development of schistosomiasis is skin exposure to contaminated fresh water and travel to endemic areas.

Risk factors in the development of schistosomiasis include:

• Exposure to contaminated fresh water
• Travel to endemic area^[1][2]

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]

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.

If left untreated, most of the patients with schistosomiasis may progress to develop ulceration or cancer of the bladder, liver or kidney failure.^[1]

Common complications of schistosomiasis include:^[2][3]

• Hematuria
• Malnutrition
• Growth retardation
• Anemia of chronic disease
• Cervicitis
• Iron-deficiency anemia
• Splenomegaly
• Intestinal polyps
• Hydronephrosis
• Glomerulonephritis
• Recurrent Salmonella bacteremia
• Bladder polyps
• Bladder cancer
• Infertility
• Ectopic pregnancy
• Portal hypertension
• Esophageal varices
• Ascites
• Intestinal obstruction
• Obstructive uropathy
• Renal failure
• Generalized seizures
• Spinal cord compression
• Cor pulmonale

• Depending on the extent of the disease progression at the time of diagnosis, the prognosis of schistosomiasis may vary.
• Prognosis is good with treatment.
• The 1-year mortality rate of patients with schistosomiasis ranges approximately 0.1-11% depending upon underlying complications.
• If symptoms of schistosomiasis persists after 2 rounds of praziquantel treatment, more urine or stool samples should be taken and tested for viable parasite eggs, and re-treatment must be given if persistent infection is detected.^[4][5]