Schistosomiasis

Schistosomiasis

 

Schistosomiasis, a highly prevalent parasitic tropical disease especially in sub-Saharan Africa, causes substantial morbidity and mortality.

Epidemiology

  • Prevalence – >200 million people world-wide are infected
  • Age – highest prevalence in children
  • Transmission – from water with snails as intermediate hosts
    • Occurs in South America, Africa, Southeast Asia and the Middle East

Risk Factors

  • Rural areas with inadequate sanitation and water supplies

Organism

  • Human infection is caused by trematode of the family Schistosomatidae
  • Common schistosomes species that infect humans
    • S. mansoni – Africa, Latin America
    • S. hematobium – Middle East, Africa
    • S. japonicum – East Asia, Pacific
    • S. intercalatum – sub-Saharan Africa
    • S. mekongi – Cambodia, Laos
  • The parasite has a complex life cycle
    • Involves an intermediate stage host – freshwater snails which release cercarial into fresh water until they find a definitive host to penetrate

Risk Factors

  • Rural areas with inadequate sanitation and water supplies

Clinical Presentation

  • Schistosome dermatitis (known as swimmers itch)
    • Infection from cercariae of Schistosoma spp that infect birds or aquatic mammals
    • Common in the Great Lakes region, New England and other parts of the U.S.
    • Itchy macular rash caused by cercaria entering the skin and dying
    • Self-limited
  • Acute schistosomiasis (also known as Katayama syndrome)
    • Systemic hypersensitivity reaction that may occur 2-8 weeks after infection
    • Fever, myalgia, nonproductive cough, fatigue, abdominal pain, eosinophilia and occasionally bloody stools
    • Liver, spleen and lymph nodes are often enlarged
    • In severe cases, death can occur with heavy infections
    • Eggs may not be seen in stools until late in the illness
  • Chronic schistosomiasis
    • Symptoms may be absent or mild especially in the patient with light or moderate egg burden
    • Peripheral blood – eosinophilia is often present
    • Fatigue, colicky abdominal pain, intermittent diarrhea or dysentery
    • Anemia due to blood loss
    • Species-specific symptoms and diseases
      • Periportal fibrosis which may lead to hepatic failure – S. mansoni and S. japonicum
      • Hematuria and dysuria – S. haematobium
        • In later stages of the disease, fibrosis of the bladder may occur which can lead to renal failure and squamous cell cancer of the bladder
      • Neurologic disease (all Schistosoma)
        • Brain infection
        • Myelopathy (most common sites are conus medullaris and cauda equina)

Diagnosis

  • Indications for testing
    • History of fresh water exposure in endemic areas and hematuria
  • Laboratory testing
    • Microscopic examination of urine, feces or tissue for viable eggs
    • ELISA IgG testing
    • Histopathology (colon, bladder, lung)

Treatment

  • Indicated for all patients with schistosomiasis
  • Antiemetic agents such as praziquantel are used

Prevention

  • Avoid contact with fresh water in infested area
  • DEET mosquito repellants may be beneficial against cercariae if applied before contact with water