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Schistosoma mansoni is a blood fluke that causes a disease commonly called Schistosomiasis or Bilharzia. There are many species of schistosoma parasites but schistosoma mansoni affects the gastrointestinal tract, hence it mainly causes intestinal Schistosomiasis.
Schistosoma Mansoni Epidemiology
Schistosoma mansoni is most common in Africa (Nile delta, Libya, southern Sudan, Senegal, Gambia, Cameroon and Zaire) and Latin America (including Puerto Rico); it is also found in Central America, South America and Europe.
Schistosoma Mansoni Transmission
Transmission of schistosoma mansoni occurs when the cercariae (larvae) penetrate the human skin. This usually occurs during swimming or contact with infected water. The freshwater snail of the genus Biomphalaria and Australorbis serves as the intermediate host.
Schistosoma mansoni Pathogenesis
The symptoms and signs mostly seen in schistosoma mansoni infection occur as a result of the passage of the eggs through the mucosa. Schistosoma mansoni affects the gastrointestinal tract directly but affects the urogenital tract indirectly by causing immune complex mediated Glomerulonephritis. The parts of the gut damaged by schistosoma mansoni include the large bowel, the liver, colon and rectum.
Stages of Schistosoma mansoni infection (Intestinal Schistosomiasis Stages and associated Clinical features)
- Stage 1 (stage of Invasion): This stage shows the first clinical signs and symptoms of acute infection and usually the symptoms appear within 24 to 48 hours after exposure. This stage is characterized by itching at the sites of entry of the cercariae, the itch is commonly known as Swimmers itch.
- Stage 2 ( Toxemia stage/ Katayama syndrome) this stages present with an early allergic manifestation resulting from egg deposition. The symptoms and signs of this stage forms a syndrome known as Katayama Syndrome or Katayama Fever and they include Fever, headache, chills, muscle pains, Malaise, diarrhea and vomiting. There may be generalized lymphadenopathy, hepatosplenomegaly, urticaria and leukocytosis with marked eosinophilia.
- Stages 3 and 4 (Chronic stage) this occurs about 3 months to several years after infection and is due to deposition of eggs in the tissues. There may be lethargy, recurrent bloody diarrhea and in some cases, intestinal polyps (bilharziomas) and progressive fibrosis of the intestinal wall leading to formation of strictures; intestinal obstruction is very rare. Other manifestations may include granulomatous hepatitis followed by progressive peri-portal fibrosis (also called pipe stem fibrosis) resulting in portal hypertension with associated splenomegaly, ascites and esophageal varices that occasionally may bleed.
Schistosoma mansoni Symptoms
- Gastrointestinal hemorrhage
- Massive splenomegaly
- Myalgias (Muscle pains)
- Profuse diarrhea
- Nausea and vomiting
- There may be generalized lymphadenopathy
Leukocytosis with marked eosinophilia
Schistosoma Mansoni Life cycle
- The schistosoma mansoni eggs are released by the adult worms in feces. The ova of Schistosoma mansoni is used for diagnosis by identifying the lateral spine of the egg
- The released Schistosoma mansoni eggs then hatch into immature ciliated larvae known as Miracidia which then penetrate only Biomphalaria and Australorbis type of freshwater snails and carry out asexual reproduction and develop into Sporocysts
- Sporocysts now develop into mature larvae named as:Cercariaewhich is infective stage of Schistosoma mansoni.
- Cercariae can now penetrate the human skin to cause Schistosomiasis. When in the body tissue, cercariae lose their tails and are now called Schistosomutae. These Schistosomutae enter the superior mesenteric artery pass into the portal circulation and reach the liver and mature into adults; the adults migrate against the portal flow to reside in the mesenteric venules.
- Adult Schistosoma mansoni worms lay eggs that are then released in stool and the life cycle continues
The life cycle of Schistosoma takes about 12 to 14 weeks to complete.
Schistosoma mansoni Characteristics
- Adult schistosomes exist as separate sexes but live attached to each other
- The female adult schistosome resides in a groove in the male this groove is called the gynecophoric canal (“schist”)
- The male schistosome then continuously fertilizes the female eggs in the gynecophoric canal
- S. mansoni and S. japonicum adults live in the mesenteric veins, whereas Schistosomahaematobium lives in the veins draining the urinary bladder. Schistosomes are therefore known as blood flukes.
Schistosoma mansoni Morphology
- Mature schistosoma larvae are called cercariae and they look like little tadpoles with oral suckers on one end and a tail on the other
- Male adult worms measure 610 mmwhile females are 715 mmin length
Schistosoma Mansoni Egg
The schistosoma mansoni eggs when viewed with a microscope can be seen to have an ovoid shape with a prominent lateral spine. The egg measures about 112 to 175 micrometer by 45 to 70 micrometer. Schistosoma mansoni eggs are capable of damaging the wall of the distal colon (inferior mesenteric venules) by digesting the tissue with proteolytic enzymes.
Schistosoma mansoni Diagnosis
- Diagnosis of Schistosoma mansoni infection is made using a light microscope by identifying the characteristic ova in feces which can easily be identified the large lateral spine
- Sigmoidoscopy and rectal snip helps to identify lesions and ova of the parasite
- Ultrasound of liver and spleen can demonstrate peri-portal fibrosis and spleen enlargement
Schistosoma Mansoni Treatment
- The drug of choice in the treatment of Schistosoma mansoni infection is Praziquantel and it is usually given orally as 40mg/kg single dose
- Oxaminoquine is also an alternative drug that is effective against Schistosoma mansoni but not used for other types of Schistosoma species; the drug dosage is 15mg/kg orally and given once for sensitive strains.
Schistosoma mansoni Complications
- Liver cirrhosis
- Portal hypertension
- Intestinal Stricture (in rare cases)
Schistosoma mansoni Prevention
- Proper disposal of human waste to avoid washing of eggs into water bodies
- Destroying snail populations if possible
- Avoid Swimming in endemic areas of schistosoma mansoni infection