Schistosoma

Background

• Trematode (blood fluke)

Microbiology

• Three main species affecting humans:
  • Schistosoma mansoni: liver and gut
  • Schistosoma haematobium: GU/pelvis
  • Schistosoma japonicum: liver and gut
• Also: Schistosoma mekongi, Schistosoma intercalatum, Schistosoma guineensis, and case reports of hybrid schistosomes of cattle origin that can infect humans
• Non-human-host schistosomes (of birds and mammals) can cause cercarial dermatitis

Risk Factors

• Fresh water exposure in endemic countries

Epidemiology

Region	Species	Seroprevalence in Migrants1
Latin America and the Caribbean	Schistosoma mansoni (Brazil, Venezuela, Suriname, Caribbean)	20%
Middle East and northern Africa	Schistosoma haematobium, Schistosoma mansoni (sporadic reports in Arabian Peninsula)	6%
Sub-Saharan Africa	Schistosoma mansoni, Schistosoma haematobium, Schistosoma intercalatum (DRC), Schistosoma guineensis (West Africa)	24%
South Asia	None	0%
East Asia and the Pacific	Schistosoma japonicum (China, Philippines, Sulawesi), Schistosoma mekongi (Cambodia, Laos)	5%

Clinical Manifestations

Swimmer's Itch

• Cercariae penetrate exposed skin and cause prickling sensation and occasionally urticaria, followed hours later by a macular rash
• Caused by schistosomes that do not cause systemic illness
• Common in Great Lakes region of North America, New England in the US, and other parts of North America and Europe

Katayama Fever

• Syndrome of acute schistosomiasis that follows 4 to 8 weeks (range 2 to 12 weeks), after the flukes have migrated, developed into adults, and have started producing eggs
• The syndrome represents a hypersensitivity reaction to the eggs produced by adult worms
• More common with Schistosoma japonicum and Schistosoma mansoni, and less common with Schistosoma haematobium
• Symptoms include abrypt onset of fever, chills, fatigue, headache, myalgias, abdominal pain, diarrhea, and occasionally bloody stool
• Most also develop cough, dyspnea, chest pain, and diffuse infiltrates on chest x-ray
  • Lung nodules contain granulomas around eggs
• Hepatomegaly, splenomegaly, and lymphadenopathy are common
• Eggs may not be seen in stool until later in the course of the disease
• Symptoms usually resolve within 2 to 10 weeks
• Can involve symptoms anywhere the worms migrate and deposit eggs: CNS, genital tract, and skin
  • However, an induced small-vessel vasculitis can also cause neurological symptoms

Chronic Schistosomiasis

• Can be asymptomatic or paucisymptomatic
• Chronic granulomatous inflammation causes weight loss, anemia, stunted growth
• Eosinophilia is common

Pulmonary Hypertension

• Primarily Schistosoma mansoni2

Investigations

• Labs
  • CBC, showing eosinophilia
  • Schistosoma serology (only positive 6 weeks after infection)
  • Egg detection in stool, urine, semen, or tissue biopsy
• Imaging
  • Eggs can cause granulomatous disease in various organs
  • Bladder polyps and obstruction may be seen on ultrasound

Diagnosis

• Usually based on serology
  • Can cross-react with other helminth co-infections, including trichinosis and filariasis
  • Can remain positive and even fluctuate for years after cure3

Management

• Acute
  • Praziquantel 40mg/kg given over one day split into 3 doses
• Chronic
  • Praziquantel 20-40 mg/kg or 40-60 mg/kg (if at risk for S. japonica)
  • Given over one day split into 3 doses
  • May be repeated 6 weeks later, though this practice is not universal
  • No role for test-of-cure serology

Prognosis

• Increased risk of squamous cell carcinoma, which increase with young age at infection, duration of infection, high burden of infection, and bladder wall fibrosis