What is the difference between Schistosoma mansoni and Schistosoma haematobium?

S. mansoni lives mainly in the inferior mesenteric veins, passes eggs with a prominent lateral spine in stool, and causes intestinal and hepatosplenic disease with periportal pipestem fibrosis and portal hypertension. S. haematobium lives in the venous plexus around the bladder, passes eggs with a terminal spine in urine, and causes hematuria, bladder fibrosis and calcification, and squamous cell carcinoma of the bladder. S. mansoni occurs in Africa, the Middle East, South America and the Caribbean, while S. haematobium occurs in Africa and the Middle East.

Which Schistosoma egg has a terminal spine?

Schistosoma haematobium eggs have a conspicuous terminal spine and are found in urine, ideally collected between noon and 3 PM. S. mansoni eggs have a prominent lateral spine and are found in stool. S. japonicum eggs are rounder, with only a small, inconspicuous spine, and are also found in stool.

Why does schistosomiasis cause portal hypertension without liver failure?

Eggs of S. mansoni and S. japonicum are carried by portal blood into the liver, where Th2-mediated granulomas form around them and lay down periportal (Symmers pipestem) fibrosis. The obstruction is presinusoidal, so hepatocytes are largely spared and albumin, bilirubin and INR usually stay normal. Patients present instead with splenomegaly, hypersplenism and esophageal varices that can bleed.

What cancer is associated with Schistosoma haematobium?

Chronic Schistosoma haematobium infection is associated with squamous cell carcinoma of the bladder. Inflammation around eggs trapped in the bladder wall causes squamous metaplasia, which can progress to cancer. By contrast, more than 90% of bladder cancers in the United States are urothelial carcinomas and only about 2% to 7% are squamous cell carcinomas.

How do people get schistosomiasis?

People are infected through skin contact with fresh water, such as lakes, rivers and irrigation canals, that contains cercariae released by infected snails. The cercariae penetrate intact skin, become schistosomula, mature in the liver and settle in the mesenteric or bladder veins, where they lay eggs. Salt water and adequately chlorinated swimming pools are safe, and there is no vaccine.

What is the treatment for schistosomiasis?

Praziquantel is the drug of choice for all Schistosoma species and is given over a single day; the FDA-labeled dose is 20 mg/kg three times in one day. It works best against adult worms, so in acute schistosomiasis (Katayama syndrome) severe symptoms are eased with a short course of low-dose prednisone, praziquantel is given once symptoms settle, and it is repeated 4 to 6 weeks later when the worms have matured. Praziquantel is contraindicated in ocular cysticercosis and with strong CYP3A4 inducers such as rifampin.

Schistosoma USMLE Question: Egg Spines, Liver vs Bladder

Schistosoma species are blood flukes: freshwater snails release cercariae that penetrate intact skin, the adult worms pair up inside veins, and the eggs, not the worms, cause the disease by provoking granulomas and fibrosis. S. mansoni and S. japonicum live in the mesenteric veins, pass eggs in stool and cause periportal "pipestem" fibrosis with presinusoidal portal hypertension (varices, splenomegaly) while liver function is usually preserved. S. haematobium lives in the venous plexus around the bladder, passes eggs in urine and causes hematuria, bladder calcification and squamous cell carcinoma of the bladder. The egg settles most questions (lateral spine = mansoni, terminal spine = haematobium, small inconspicuous spine = japonicum), and praziquantel treats every species.

The Q-bank vignette

A 29-year-old man who grew up in a river town in northeastern Brazil and moved to the United States 3 years ago vomits a large amount of bright red blood. He does not drink alcohol. His spleen is palpable 6 cm below the costal margin, and he has no jaundice, ascites, spider angiomas or asterixis. Albumin, bilirubin, INR and aminotransferases are normal; the platelet count is 82,000/µL. Endoscopy shows large esophageal varices. Ultrasound shows a normal-sized, smooth liver with thick echogenic bands around the portal vein branches. Stool microscopy shows oval eggs about 150 µm long with a prominent lateral spine.

Infection with which organism is the most likely cause?

A. Clonorchis sinensis
B. Echinococcus granulosus
C. Hepatitis B virus
D. Schistosoma haematobium
E. Schistosoma japonicum
F. Schistosoma mansoni

Answer: F. Schistosoma mansoni.

Why it's Schistosoma mansoni

Geography: S. mansoni is the only one of the major human schistosomes found in the Americas (Brazil, Venezuela, Suriname and the Caribbean); it also occurs across Africa and the Middle East.
The egg: oval, 114–180 µm long, with a prominent lateral spine near one end, passed in stool.
Where the adults live: mostly in the inferior mesenteric veins draining the large bowel. Eggs that fail to cross the bowel wall are carried by portal blood into the liver.
What the eggs do: each trapped egg provokes a Th2-mediated granuloma (the type 2 response is covered in Th1 vs Th2 immune responses). Over years, this lays down periportal "pipestem" (Symmers) fibrosis.
Why the liver still works: schistosomiasis is a presinusoidal cause of portal hypertension, so hepatocyte function is spared: normal albumin, bilirubin and INR, but splenomegaly, hypersplenism and varices. The varices can bleed and cause hematemesis, as in this patient.
The lungs: once portosystemic collaterals open, eggs can bypass the liver and lodge in the pulmonary vessels, causing pulmonary hypertension and cor pulmonale.

S. mansoni vs S. japonicum vs S. haematobium

Feature	S. mansoni	S. japonicum	S. haematobium
Where	Sub-Saharan Africa, Middle East, Brazil, Venezuela, Suriname, Caribbean	China, Philippines, Indonesia	Africa, Middle East
Snail host	Biomphalaria	Oncomelania	Bulinus
Adult worms (mostly)	Inferior mesenteric veins (large bowel)	Superior mesenteric veins (small bowel)	Vesical and pelvic venous plexus (bladder)
Egg	114–180 µm, prominent lateral spine	70–100 µm, rounder, small, inconspicuous spine	110–170 µm, terminal spine
Specimen	Stool	Stool	Urine, ideally collected between noon and 3 PM
Chronic disease	Intestinal (pain, diarrhea, blood in stool, polyps) and hepatosplenic: pipestem fibrosis, portal hypertension, varices	Same pattern, often heavier: about 500–3,500 eggs a day vs 100–300 for S. mansoni	Urogenital: hematuria, dysuria, bladder fibrosis and calcification, ureteral strictures, hydronephrosis
Board-favorite complication	Variceal bleeding; spinal cord disease (transverse myelitis)	Variceal bleeding; most brain schistosomiasis (seizures)	Squamous cell carcinoma of the bladder; female genital schistosomiasis

Life cycle and timeline

Eggs reach fresh water in stool or urine and hatch into miracidia, which infect a specific snail.
The snail releases fork-tailed cercariae that penetrate intact skin during swimming, bathing or wading.
They shed their tails and become schistosomula, which travel in venous blood to the lungs and heart, mature in the liver, pair up and move to their final veins.
Adults are coated with host antigens and survive for years (Merck cites estimates of 3–7 years).
Eggs appear in stool or urine 1–3 months after exposure.

Phase	Timing	What you see
Cercarial dermatitis	Hours to a week after exposure	Itchy papular rash where cercariae entered
Acute schistosomiasis (Katayama syndrome)	Usually 14–84 days, around the onset of egg laying	Fever, headache, myalgia, cough, urticaria, diarrhea, marked eosinophilia, hepatosplenomegaly; more common and more severe in visitors than in residents of endemic areas
Chronic schistosomiasis	Years	Egg granulomas and fibrosis in the bowel and liver, or in the bladder and genital tract

Why every other answer choice is wrong

A. Clonorchis sinensis. Also a fluke with a snail host, but it lives in the bile ducts, not the portal veins, and is caught from raw, pickled or smoked freshwater fish in East Asia. It causes right upper quadrant pain, cholangitis, stones and cholangiocarcinoma (see the cholangiocarcinoma guide). Its eggs are tiny (27–35 µm) and operculated, with the lid resting on "shoulders" and a small knob, not a spine, at the other end.

B. Echinococcus granulosus. The dog tapeworm. Humans swallow eggs from dog feces and become accidental intermediate hosts, growing hydatid cysts in the liver or lungs; a ruptured cyst can cause anaphylaxis. Humans pass no eggs in stool, and the lesion is a cyst, not periportal fibrosis.

C. Hepatitis B virus. HBV cirrhosis causes sinusoidal portal hypertension with a nodular liver and failing synthetic function (low albumin, prolonged INR, jaundice). Normal liver function with spined eggs in stool points to a presinusoidal, parasitic cause. The cirrhosis pattern is laid out in the cirrhosis and portal hypertension guide.

D. Schistosoma haematobium. Right genus, wrong veins: it lives around the bladder, sheds terminal-spined eggs in urine and presents with hematuria. It occurs in Africa and the Middle East, not Brazil.

E. Schistosoma japonicum. Same hepatosplenic disease, often more severe because it lays many more eggs, but it is an Asian species, and its rounder egg has only a small, inconspicuous spine.

Worked example: the urinary version

Vignette. A 44-year-old farmer from a village in sub-Saharan Africa has had blood in his urine on and off since boyhood and was never treated. He has never smoked or worked with industrial chemicals. He now has painless gross hematuria. A plain film shows a thin line of calcification outlining the bladder wall, cystoscopy shows an exophytic bladder mass, and urine microscopy shows eggs with a terminal spine. Biopsy of the mass is most likely to show which tumor?

Answer: squamous cell carcinoma. Chronic inflammation around trapped S. haematobium eggs drives squamous metaplasia of the bladder lining, and the National Cancer Institute lists S. haematobium infection ("bilharzial bladder cancer") as a bladder cancer risk factor.

Why not the others?

Urothelial (transitional cell) carcinoma: more than 90% of US bladder cancers, versus about 2–7% for squamous cell carcinoma. Think smoking (up to half of all bladder cancers), aromatic amines from dye, paint, metal and petroleum work, cyclophosphamide or ifosfamide, pelvic radiation and arsenic.
Adenocarcinoma: about 2% of US bladder cancers; it arises from a urachal remnant or from glandular metaplasia of chronically irritated epithelium.
Cholangiocarcinoma: the liver fluke cancer (Clonorchis, Opisthorchis), not a blood fluke cancer.

Diagnosis and treatment

Microscopy: eggs in stool (S. mansoni, S. japonicum) or urine (S. haematobium). Repeated or concentrated samples raise the yield, and a rectal or bladder biopsy can show eggs in tissue.
Serology: helpful in light infections and returning travelers, but it cannot separate past from current infection, and Merck advises waiting at least 6–12 weeks after the last freshwater exposure before testing.
Praziquantel for every species. The FDA label dose is 20 mg/kg three times in 1 day, 4–6 hours apart; Merck lists 2 doses for S. haematobium and S. mansoni and 3 for S. japonicum and S. mekongi. It changes the worm's membrane permeability (to calcium, in the usual board phrasing), causing rapid contraction and breakdown of the tegument.
Acute schistosomiasis: CDC notes that praziquantel works best against adult worms and needs a mature antibody response, so treatment given too early may have to be repeated. Merck advises 5 days of low-dose prednisone for severe symptoms, then praziquantel once symptoms settle, repeated 4–6 weeks later when the worms have matured. For light infections, the Yellow Book notes that a repeat course after 2–4 weeks may be needed.
Praziquantel contraindications: ocular cysticercosis and strong CYP3A4 inducers such as rifampin.
Prevention: avoid freshwater contact in endemic areas; salt water and adequately chlorinated pools are safe, and there is no vaccine. WHO estimates that at least 253.7 million people needed preventive praziquantel in 2024, about 94% of them in Africa.

Exam traps

Haematobium sounds like hematuria: bladder, urine, terminal spine. Mansoni and japonicum are the gut-and-liver species.
Varices with normal liver function = presinusoidal portal hypertension: think schistosomiasis in anyone from an endemic area.
Bladder squamous cell carcinoma in a non-smoker from Africa or the Middle East = S. haematobium; in a US smoker, bladder cancer is usually urothelial.
Liver fluke vs blood fluke: Clonorchis (raw fish, bile ducts) → cholangiocarcinoma; Schistosoma (skin contact with fresh water, veins) → pipestem fibrosis or bladder cancer.
Swimmer's itch after a US lake is cercarial dermatitis from schistosomes of birds (ducks, geese, gulls) and some mammals. Their larvae burrow into the skin but cannot develop in humans, so they cause only a self-limited itchy rash, not schistosomiasis.
Female genital schistosomiasis (S. haematobium) causes bleeding, pain with intercourse and infertility, and raises the risk of acquiring HIV.

Key takeaways

Schistosomes enter through skin in fresh water (cercariae from snails); the eggs cause disease through Th2 granulomas and fibrosis.
S. mansoni: lateral spine, stool, inferior mesenteric veins, pipestem fibrosis → presinusoidal portal hypertension with preserved liver function; the only major species in the Americas.
S. japonicum: Asia, small inconspicuous spine, superior mesenteric veins, heaviest egg output, most brain cases.
S. haematobium: terminal spine, urine, bladder venous plexus, hematuria, bladder calcification, squamous cell carcinoma.
Katayama syndrome (fever, urticaria, eosinophilia) appears about 2–12 weeks after exposure.
Praziquantel treats all species.