Schistosomiasis

Schistosomiasis is infestation by a parasitic blood worm that can damage the liver, bladder, and intestines

Schistosomiasis itch

Schistosomiasis itch

Other names

Schistosomiasis, also known as bilharzia, is a disease caused by parasitic worms.

Clinical features

Although the worms that cause schistosomiasis are not found in the United States, people are infected worldwide. In terms of impact this disease is second only to malaria as the most devastating parasitic disease. Schistosomiasis is considered one of the neglected tropical diseases (NTDs). The parasites that cause schistosomiasis live in certain types of freshwater snails. The infectious form of the parasite, known as cercariae, emerge from the snail into the water. You can become infected when your skin comes in contact with contaminated freshwater. Most human infections are caused by Schistosoma mansoni, S. haematobium, or S. japonicum.

S mansoni egg

S mansoni egg

Diagnosis

• Examination of stool and/or urine for ova is the primary method of diagnosis for suspected schistosome infections.
• The choice of sample to diagnose schistosomiasis depends on the species of parasite likely causing the infection.
• Adult stages of S. mansoni, S. japonicum, S. mekongi, and S. intercalatum reside in the mesenteric venous plexus of infected hosts and eggs are shed in feces;
• S. haematobium adult worms are found in the venous plexus of the lower urinary tract and eggs are shed in urine.

Schistosomiasis Life Cycle

Schistosomiasis Life Cycle

Travel and other history

Careful review of travel and residence history is critical for determining whether infection is likely and which species may be causing infection.

Serological tests

• Serologic testing for antischistosomal antibody is indicated for diagnosis of travelers or immigrants from endemic areas who have not been treated appropriately for schistosomiasis in the past.
• Commonly used serologic tests detect antibody to the adult worm.
• For new infections, the serum sample tested should be collected at least 6 to 8 weeks after likely infection, to allow for full development of the parasite and antibody to the adult stage.
• Serologic testing may not be appropriate for determination of active infection in patients who have been repeatedly infected and treated in the past because specific antibody can persist despite cure.
• In these patients, serologic testing cannot distinguish resolved infection from active infection.
• An antigen test has been developed that can detect active infection based on the presence of schistosomal antigen, but this test is not commercially available in the United States and at this time is undergoing field evaluations for accurate diagnosis of low-intensity infections.

Schistosomiasis haematobia

Schistosomiasis haematobia

Incubation

• The incubation period for patients with acute schistosomiasis is usually 14-84 days; however, many people are asymptomatic and have subclinical disease during both acute and chronic stages of infection.
• Persons with acute infection (also known as Katayama syndrome) may present with rash, fever, headache, myalgia, and respiratory symptoms. Often eosinophilia is present with hepato- and/or splenomegaly.

DPDx Resources

• DPDx: Schistosomiasis
• Specimen collection: Stool
• Specimen collection: Urine

Pathophysiology

Clinical manifestations of chronic disease result from host immune responses to schistosome eggs.

Schistosomiasis in a child

Schistosomiasis in a child

Treatment

• Infections with all major Schistosoma species can be treated with praziquantel.
• The timing of treatment is important since praziquantel is most effective against the adult worm and requires the presence of a mature antibody response to the parasite.
• For travelers, treatment should be at least 6-8 weeks after last exposure to potentially contaminated freshwater.
• 
  

Schistosoma species infection	Praziquantel dose and Duration
Schistosoma mansoni, S. haematobium, S. intercalatum	40 mg/kg per day orally in two divided doses for one day
S. japonicum, S. mekongi	60 mg/kg per day orally in three divided doses for one day

Safety

• There is a lack of safety trial data for the use of praziquantel in children less than 4 years of age or pregnant women.
• WHO reports that there is growing evidence that infected children as young as 1 year old can be effectively treated with praziquantel without serious side effects; however, the drug is commonly available in the form of large, hard-to-swallow pills, which puts young children at risk for choking and other difficulties swallowing the drug.

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