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11-year-old boy with abdominal fluid and portal hypertension due to schistosomiasis (Agusan del Sur, Philippines)
Classification and external resources
Specialty Infectious disease
ICD-10 B65
ICD-9-CM 120
MedlinePlus 001321
MeSH D012552

Schistosomiasis, also known as bilharzia, snail fever, and Katayama fever,[1][2] is a disease caused by

  • Schistosomiasis at DMOZ
  • UNHCO site on Schistosomiasis
  • River of Hope — documentary about the rise of schistosomiasis along the Senegal river (video, 47 mins)
  • Schistosomiasis information for travellers from IAMAT (International Association for Medical Assistance to Travellers)

External links

Further reading

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  11. ^ p.771 Robbin and Cotran Pathological Basis of Disease 8th
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  17. ^ WHO (2013) Schistosomiasis: Progress report 2001–2011, strategic plan 2012–2020. Geneva: World Health Organization.
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  30. ^ a b Luke F. Pennington and Michael H. Hsieh (2014) Immune Response to Parasitic Infections, Bentham e books, Vol 2, pp. 93-124, ISBN 978-1-60805-148-9
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  33. ^ "Proceedings of the 13h Annual History of Medicine Days", a medical historical paper from University of Calgary. March 2004.
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  41. ^ See, for example,
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Mirazid, an Egyptian drug made from myrrh, was under investigation for oral treatment of the disease up until 2005.[41] The efficacy of praziquantel was proven to be about eight times than that of Mirazid and therefore Mirazid was not recommended as a suitable agent to control schistosomiasis.[42]

The Bill & Melinda Gates Foundation has recently funded an operational research program — the Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) to answer strategic questions about how to move forward with schistosomiasis control and elimination. The focus of SCORE is on development of tools and evaluation of strategies for use in mass drug administration campaigns.

As with other major parasitic diseases, there is ongoing and extensive research into developing a schistosomiasis vaccine that will prevent the parasite from completing its life cycle in humans. In 2009, Eurogentec Biologics developed a vaccine against bilharziosis in partnership with INSERM and researchers from the Pasteur Institute.[38][39][40]


Schistosomiasis was mentioned in an episode of the television sitcom WKRP in Cincinnati. In the episode "Frog Story" from season 3, Dr. Johnny Fever becomes concerned that he may have schistosomiasis.[37] Among human parasitic diseases, schistosomiasis ranks second behind malaria in terms of socio-economic and public health importance in tropical and subtropical areas.

Schistosomiasis is endemic in Egypt, exacerbated by the country's dam and irrigation projects along the Nile. From the late 1950s through the early 1980s, infected villagers were treated with repeated injections of tartar emetic. Epidemiological evidence suggests that this campaign unintentionally contributed to the spread of hepatitis C via unclean needles. Egypt has the world's highest hepatitis C infection rate, and the infection rates in various regions of the country closely track the timing and intensity of the anti-schistosomiasis campaign.[34] From ancient times to the early 20th century, schistosomiasis' symptom of blood in the urine was seen as a male version of menstruation in Egypt and was thus viewed as a rite of passage for boys.[35][36]

Society and culture

It was a common cause of death for Ancient Egyptians in the Greco-Roman Period.[33]

The first physician who described the entire disease cycle was Brazilian parasitologist Pirajá da Silva in 1908. The first known case of infection was discovered in 2014, it belongs to a child who lived 6,200 years ago.[32]

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.


[25].neglected tropical diseases It is the most deadly of the [31] Another 20 million have severe consequences from the disease.[7][3] Estimates regarding the number of deaths vary. Worldwide in 2010 the


Schistosoma haematobium, the infectious agent responsible for urogenital schistosomiasis, infects over 112 million people annually in Sub-Saharan Africa alone.[30] It is responsible for 32 million cases of dysuria, 10 million cases of hydronephrosis, and 150,000 deaths from renal failure annually, making Schistosoma haematobium the world’s deadliest schistosome.[30]

In 2010, approximately 238 million people were infected with schistosomiasis, 85% of whom live in Africa.[26] An earlier estimate from 2006 had put the figure at 200 million people infected.[27] In many of the affected areas, schistosomiasis infects a large proportion of children under 14 years of age. An estimated 600 to 700 million people worldwide are at risk from the disease because they live in countries where the organism is common.[7][25] In 2012, 249 million people were in need of treatment to prevent the disease.[28] This likely makes it the most common parasitic infection with malaria second and causing about 207 million cases in 2013.[25][29]

Infection estimates

The disease is common in about 75 developing countries and mainly affects people living in rural agricultural and peri-urban areas.[24][25]

The disease is found in tropical countries in Africa, the Caribbean, eastern South America, Southeast Asia and in the Middle East. Schistosoma mansoni is found in parts of South America and the Caribbean, Africa, and the Middle East; Schistosoma haematobium in Africa and the Middle East; and Schistosoma japonicum in the Far East. Schistosoma mekongi and Schistosoma intercalatum are found locally in Southeast Asia and central West Africa, respectively.

Disability-adjusted life year for schistosomiasis per 100,000 inhabitants.
  no data
  less than 50
  more than 500


Another agent, mefloquine, which has previously been used to treat malaria, was recognised in 2008–2009 to be effective against schistosoma.[23] Mefloquine may be used in combination with praziquantel or artemisinins. Its mechanism of action is not known but it causes extensive and severe morphological, histopathological, and ultrastructural damage to adult and juvenile schistosomes, particularly, the worm tegument, musculature, gut, and vitelline glands of female worms.

Other possible treatments include a combination of praziquantel with metrifonate, artesunate or mefloquine.[22] A Cochrane review found tentative evidence that when used alone metrifonate was as effective as praziquantel.[22]

  • When a village reports more than 50 percent of children have blood in their urine, everyone in the village receives treatment.[21]
  • When 20 to 50 percent of children have bloody urine, only school-age children are treated.[21]
  • When fewer than 20 percent of children have symptoms, mass treatment is not implemented.[21]

The World Health Organization has developed guidelines for community treatment based on the impact the disease has on children in villages in which it is common:[21]

Schistosomiasis is treatable using a single dose of the drug praziquantel by mouth annually.[21]

Ethiopian children treated for schistosoma mansoni


While guidelines on how to design these schemes to minimise the spread of the disease had been published years before, but the designers were unaware of them.[20]

For many years from the 1950s onwards, vast dams and irrigation schemes were constructed, causing a massive rise in water-borne infections from schistosomiasis. The detailed specifications laid out in various UN documents since the 1950s could have minimized this problem. Irrigation schemes can be designed to make it hard for the snails to colonize the water, and to reduce the contact with the local population.[19]

Prevention is best accomplished by eliminating the water-dwelling snails that are the natural reservoir of the disease. Acrolein, copper sulfate, and niclosamide can be used for this purpose. Recent studies have suggested that snail populations can be controlled by the introduction of, or augmentation of existing, crayfish populations.


A 2014 review found tentative evidence that increasing access to clean water and sanitation reduces schistosome infection.[18]

A few countries have eradicated the disease, and many more are working toward it. The praziquantel is used for prevention in high-risk populations living in areas were the disease is common.[17]


Antibody detection can be useful in both clinical management and for epidemiologic surveys.

The eggs of S. haematobium are ellipsoidal with a terminal spine, S. mansoni eggs are also ellipsoidal but with a lateral spine, S. japonicum eggs are spheroidal with a small knob.

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.

Recently a field evaluation of a novel handheld microscope was undertaken in Uganda for the diagnosis of intestinal schistosomiasis by a team led by Russell Stothard from the Natural History Museum of London, working with the Schistosomiasis Control Initiative, London.[16]

Eggs can be found in the urine in infections with S. japonicum and with S. intercalatum (recommended time for collection: between noon and 3 p.m.) 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. Investigation of S. haematobium should also include a pelvic x-ray as bladder wall calcification is highly characteristic of chronic infection.

Eggs can be present in the stool in infections with all Schistosoma species. The examination can be performed on a 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). In addition, for field surveys and investigational purposes, the egg output can be quantified by using the Kato technique (20 to 50 mg of fecal material) or the Ritchie technique.

Contemporary diagnosis involves detection of parasitic antigens by ELISA; all that is required from the patient is a blood sample. This screening method is highly effective. Microscopic identification of eggs in stool or, less commonly, the urine is another way of arriving at a positive diagnosis. For the measurement of eggs in the feces of presenting patients the scientific unit used is eggs per gram (epg). Stool examination should be performed when infection with S. mansoni or S. japonicum is suspected, and urine examination should be performed if S. haematobium is suspected.

S. japonicum eggs in hepatic portal tract.
High powered detailed micrograph of Schistosoma parasite eggs in human bladder tissue.


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.

Parasites reach maturity in six to eight weeks, at which time they begin to produce eggs. Adult S. mansoni pairs residing in the mesenteric vessels may produce up to 300 eggs per day during their reproductive lives. S. japonicum may produce up to 3,000 eggs per day. Many of the eggs pass through the walls of the blood vessels, and through the intestinal wall, to be passed out of the body in feces. 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. Worm pairs can live in the body for an average of four and a half years, but may persist up to twenty years.

The newly transformed schistosomulum may remain in the skin for two days before locating a post-capillary venule; from here the schistosomulum travels 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. S. japonicum migrates more quickly than S. mansoni, and usually reaches the liver within eight days of penetration. Juvenile S. mansoni and S. japonicum worms develop an oral sucker after arriving at the liver, and it is during this period that the parasite begins to feed on red blood cells. The nearly-mature worms pair, with the longer female worm residing in the gynaecophoric channel of the shorter male. Adult worms are about 10 mm long. Worm pairs of S. mansoni and S. japonicum relocate to the mesenteric or rectal veins. S. haematobium schistosomula ultimately migrate from the liver to the perivesical venous plexus of the bladder, ureters, and kidneys through the hemorrhoidal plexus.

Photomicrography of bladder in S. hematobium infection, showing clusters of the parasite eggs with intense eosinophilia.

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 most common way of getting schistosomiasis in developing countries is by wading or swimming in lakes, ponds and other bodies of water that are infested with the snails (usually of the genera Biomphalaria, Bulinus, or Oncomelania) that are the natural reservoirs of the Schistosoma pathogen.

Cercariae emerge daily from the snail host in a circadian rhythm, dependent on ambient temperature and light. Young cercariae are highly mobile, 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.

The life cycles of all five human schistosomes are broadly similar: parasite eggs are released into the environment from infected individuals, hatching on contact with fresh water to release the free-swimming miracidium. Miracidia infect freshwater snails by penetrating the snail's foot. After infection, close to the site of penetration, the miracidium transforms into a primary (mother) sporocyst. Germ cells within the primary sporocyst will then begin dividing to produce secondary (daughter) sporocysts, which migrate to the snail's hepatopancreas. Once at the hepatopancreas, germ cells within the secondary sporocyst begin to divide again, this time producing thousands of new parasites, known as cercariae, which are the larvae capable of infecting mammals.


Schistosomes have a typical trematode vertebrate-invertebrate lifecycle, with humans being the definitive host. Infections by this parasitic worm is in a family of diseases known as helminthiases.

Schistosoma life cycle.

Life cycle


Bladder cancer diagnosis and mortality are generally elevated in affected areas.

Continuing infection may cause granulomatous reactions and fibrosis in the affected organs, which may result in manifestations that include:

Calcification of the bladder wall on a plain x-ray image of the pelvis, in a 44-year-old sub-Saharan man. This is due to urinary schistosomiasis.

Occasionally central nervous system lesions occur: cerebral granulomatous disease may be caused by ectopic S. japonicum eggs in the brain, and granulomatous lesions around ectopic eggs in the spinal cord from S. mansoni and S. haematobium infections may result in a transverse myelitis with flaccid paraplegia.[15]

  • Abdominal pain
  • Cough
  • Diarrhea
  • Eosinophilia — extremely high eosinophil granulocyte (white blood cell) count.
  • Fever
  • Fatigue
  • Hepatosplenomegaly — the enlargement of both the liver and the spleen.
    • Hepatic schistosomiasis is the second most common cause of esophageal varices[11] worldwide.
  • Genital sores — lesions that increase vulnerability to HIV infection. Lesions caused by schistosomiasis may continue to be a problem after control of the schistosomiasis infection itself. Early treatment, especially of children, which is relatively inexpensive, prevents formation of the sores.[12][13]
  • Skin symptoms: At the start of infection, mild itching and a papular dermatitis of the feet and other parts after swimming in polluted streams containing cercariae.[14]:432

Above all, schistosomiasis is a chronic disease. Many infections are subclinically symptomatic, with mild anemia and malnutrition being common in endemic areas. Acute schistosomiasis (Katayama's fever) may occur weeks after the initial infection, especially by S. mansoni and S. japonicum. Manifestations include:

Skin blisters on the forearm, created by the entrance of Schistosoma parasite

Signs and symptoms

S. bovis — normally infects cattle, sheep and goats in Africa, parts of Southern Europe and the Middle East
S. mattheei — normally infects cattle, sheep and goats in Central and Southern Africa
S. margrebowiei — normally infects antelope, buffalo and waterbuck in Southern and Central Africa
S. curassoni — normally infects domestic ruminants in West Africa
S. rodhaini — normally infects rodents and carnivores in parts of Central Africa

Species of Schistosoma that can infect other animals:

Avian schistosomiasis species cause swimmer's itch.

Species of Schistosoma that can infect humans:



  • Classification 1
  • Signs and symptoms 2
  • Pathophysiology 3
    • Life cycle 3.1
      • Snails 3.1.1
      • Humans 3.1.2
  • Diagnosis 4
  • Prevention 5
    • Snails 5.1
  • Treatment 6
  • Epidemiology 7
    • Infection estimates 7.1
    • Deaths 7.2
  • History 8
  • Society and culture 9
  • Research 10
  • References 11
  • Further reading 12
  • External links 13

[10].neglected tropical disease It is classified as a [9], as a parasitic disease with the greatest economic impact.malaria In tropical countries, schistosomiasis is second only to [8][7] Around 700 million people, in more than 70 countries, live in areas where the disease is common.[3].South America and Asia, as well as Africa The disease is most commonly found in [7] to 200,000 people die from it a year.[6] and an estimated 12,000[5] Schistosomiasis affects almost 210 million people worldwide,[3]

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