Schistosomiasis

 

• Background

  Aka bilharzia, blood fluke.

  Transmission and pathophysiology

  • A trematode (aka fluke) infection. The intermediate hosts are freshwater snails, from which Schistosoma are released as free-swimming larvae ('cercariae'), which can penetrate human skin.
  • Once through the skin, they migrate to the pulmonary vessels and then systemic circulation, mating in the portal veins.
  • Then travel to the intestines (S. mansoni and S. japonicum) or bladder (S. haematobium) to produce eggs, which are highly antigenic and induce a granulomatous response.

• Presentation

  Acute infection:

  • Usually asymptomatic or just 'swimmer's itch', an itchy papular or urticarial rash which appears a few days after exposure, typically on the lower legs or feet.
  • In some patients, Katayama fever (aka acute schistosomiasis syndrome) develops 1-2 months later: malaise, arthralgia, diarrhoea, hepatosplenomegaly, RUQ pain, lymphadenopathy, urticaria, and wheeze. Most common with S. japonicum.

  Disease burden primarily comes from chronic complications:

  • S. haematobium (Egypt): cystitis with haematuria and eventually bladder squamous cell carcinoma.
  • S. mansoni (Central Africa, South America) and S. japonicum (South East Asia): portal hypertension (which may lead to varices and haematemesis), liver disease, and splenomegaly.

• Investigations

  • Microscopy: faeces (S. Japonicum, S. mansoni), midday urine (S. haematobium).
  • Bloods: eosinophilia, serology +ve after 3 months.
  • Urinalysis: blood.

• Management

  • Praziquantel
  • Give steroids before if ↑↑eosinophils or had Katayama due to risk of paradoxical response.