Schistosomiases

Schistosomiases are acute or chronic visceral parasitic diseases due to 5 species of trematodes (schistosomes).

The three main species infecting humans are Schistosoma haematobium, Schistosoma mansoni and Schistosoma japonicumSchistosoma mekongi and Schistosoma intercalatum have a more limited distribution (see table below).

Humans are infected while wading/bathing in fresh water infested with schistosome larvae. Symptoms occurring during the phases of parasite invasion (transient localized itching as larvae penetrate the skin) and migration (allergic manifestations and gastrointestinal symptoms during migration of schistosomules) are frequently overlooked. In general, schistosomiasis is suspected when symptoms of established infection become evident (see table below).

Each species gives rise to a specific clinical form: genito-urinary schistosomiasis due to S. haematobium, intestinal schistosomiasis due S. mansoni, S. japonicum, S. mekongi and S. intercalatum.

The severity of the disease depends on the parasite load. Heavily infected patients are prone to visceral lesions with potentially irreversible sequelae.

Children aged 5 to 15 years are particularly at risk: prevalence and parasite load are highest in this age group.

An antiparasitic treatment should be administered to reduce the risk of severe lesions, even if there is a likelihood of re-infection.


Geographic distribution of schistosomiasis in Africa (WHO)



Parasite/Epidemiology

Clinical features/Diagnosis (established infection)

Treatment

Genito-urinary schistosomiasis

S. haematobium
Distribution: Africa, Madagascar and the Arabian peninsula

  • Urinary manifestations:
    • In endemic areas, urinary schistosomiasis should be suspected in any patients who complain of macroscopic haematuria (red coloured urine throughout, or at the end of, micturition). Haematuria is frequently associated with polyuria/ dysuria (frequent and painful micturition).
    • In patients, especially children and adolescents, with urinary symptoms, visual inspection of the urine (and dipstick test for microscopic haematuria if the urine appears grossly normal) is indispensible.
    • Presumptive treatment is recommended in the presence of macro- or microscopic haematuria, when parasitological confirmation (parasite eggs detected in urine) cannot be obtained.
  • Genital manifestations:
    In women, symptoms of genital infection (white-yellow or bloody vaginal discharge, itching, lower abdominal pain, dyspareunia) or vaginal lesions resembling genital warts or ulcerative lesions on the cervix; in men, haematospermia (blood in the semen).
  • If left untreated: risk of recurrent urinary tract infections, fibrosis/calcification of the bladder and ureters, bladder cancer; increased susceptibility to sexually transmitted infections and risk of infertility.
  • In endemic areas, genito-urinary schistosomiasis may be a differential diagnosis to the genito-urinary tuberculosis, and in women, to the sexually transmitted infections (especially in women with an history of haematuria).

The same antiparasitic treatment is used for all species:

praziquantel PO
Children > 2 years and adults1 :
40 mg/kg single dose

Intestinal schistosomiasis

S. mansoni
Distribution: tropical Africa, Madagascar, the Arabian peninsula, South America (especially Brazil)

S. japonicum
Distribution: China, Indonesia, the Philippines

S. mekongi
Distribution: parts of Lao PDR, Cambodia (along the Mekong River)

S. intercalatum
Distribution: parts of DRC, Congo, Gabon, Cameroon, Chad

  • Non-specific digestive symptoms (abdominal pain; diarrhoea, intermittent or chronic, with or without blood) and hepatomegaly.
  • For S. intercalatum: digestive symptoms only (rectal pain, tenesmus, rectal prolapse, bloody diarrhoea).
  • If left untreated: risk of hepatic fibrosis, portal hypertension, cirrhosis, gastrointestinal haemorrhage (hematemesis, melanea, etc.), except with S. intercalatum (less pathogenic than other intestinal schistosomes, no severe hepatic lesions).
  • The diagnosis is confirmed when parasite eggs are detected in stools.
  • In the absence of reliable parasitological diagnosis: in areas where intestinal schistosomiasis is common, diarrhoea (especially bloody diarrhoea) with abdominal pain and/or hepatomegaly may be a basis for presumptive diagnosis and treatment.



Footnotes
Ref Notes
1 For the treatment of schistosomiasis, praziquantel may me administered to pregnant women.