Schistosomiasis

Schistosomiasis is a parasitic blood fluke infection that can cause severe complications in longstanding chronic infections. It is especially prevalent in sub-Saharan Africa (see Map). Most African refugee patients will know this infection as “bilharzia”.

The adult worms can live for years in the blood vessels surrounding the patient’s organs (mainly the bowel, liver and bladder) and will produce eggs that cause inflammation as they migrate through the tissues. This inflammation can lead to complications such as bowel ulceration and blood loss, portal hypertension, hematuria and bladder cancer.

Eosinophilia is also often observed in patients with schistosomiasis.

 

POSITIVE SEROLOGY

In patients with a positive schistosoma serology, we usually inquire about potential associated symptoms such as macroscopic hematuria, dysuria, abdominal pain, diarrhea and rectorrhagia. We also look for signs of portal hypertension.

We only order abdominal imaging in patients with symptoms or signs of potential liver involvement. We currently do not recommend performing a urinalysis to look for microscopic hematuria in schistosomiasis patients, since it can lead to additional unnecessary investigations. A urinalysis is not an appropriate test-of-cure for schistosomiasis. Patients with macroscopic hematuria should however be investigated accordingly.

 

TREATMENT

In patients with a positive schistosoma serology, the treatment of choice is a single dose of praziquantel:

Praziquantel 40 mg/kg* taken in one day Can be divided in 2 separate doses (AM-PM) for better tolerance

* Because S. japonicum and S. mekongi infections require a higher dose of praziquantel, patients from Southeast Asia should instead be treated with a dose of 60 mg/kg divided in 3 doses. S. mansoni infections from Brazil should also be treated with a higher dose.
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Praziquantel​ is available in 600 mg tablets.

Side effects are usually mild and can include dizziness, headache, vomiting, abdominal pain, diarrhea, and pruritus.

Praziquantel is approved by Health Canada and is covered by the Interim Federal Health Program. It is however not available in most regular pharmacies and physicians should contact their local pharmacies to inquire about its availability.

 

CONTRAINDICATIONS TO PRAZIQUANTEL

Before being prescribed praziquantel, patients should be asked about any focal neurological symptom or a history of seizure. If this is the case, praziquantel should NOT be given to these patients since it could provoke an inflammatory response in cases of undiagnosed neuroschistosomiasis or cysticercosis. The patient should be referred to an Infectious Diseases specialist for further investigations.

Praziquantel is safe (and recommended) to use in pregnancy to treat schistosomiasis (Friedman et al., 2018). Since the effects of praziquantel during the first trimester have not been well assessed yet, it is preferable to wait until the second trimester to offer treatment.

 

TEST-OF-CURE

Unlike strongyloidiasis, a repeat serology should not be used as a test-of-cure. This is because anti-schistosoma antibodies titers can stay elevated for years after treatment. There is currently no test-of-cure available in Canada. However, if a patient with schistosomiasis also has eosinophilia, a repeat CBC can be an adequate follow-up test post-treatment (at least 4 weeks later).

 

EQUIVOCAL SEROLOGY

In patients with an equivocal schistosoma serology, a repeat serology can be ordered. On the second serology, a positive or a second equivocal result warrants treatment. However, as for strongyloidiasis, considering the simplicity and safety of the treatment, it is reasonable to offer praziquantel right away without repeating the serology.

 

>> Refer to the Centers for Disease Control and Prevention (CDC) website for more information on schistosomiasis.