What is schistosomiasis?

Schistosomiasis: Definition, Pathophysiology, and Clinical Implications

Schistosomiasis is a neglected tropical disease caused by parasitic blood flukes of the genus Schistosoma, with three major species (S. haematobium, S. mansoni, and S. japonicum) responsible for significant morbidity and mortality worldwide, particularly in sub-Saharan Africa, the Middle East, Southeast Asia, and South America. 1

Parasite Life Cycle and Transmission

• Schistosomiasis is transmitted through a complex life cycle involving freshwater snails as intermediate hosts, where the infective larvae (cercariae) develop before penetrating human skin upon contact with infested water 1, 2
• After skin penetration, the parasites mature into adult worms that reside in specific venous plexuses: mesenteric veins (S. mansoni and S. japonicum) or pelvic veins (S. haematobium) 1
• Female worms produce eggs that either pass into the environment through feces or urine, or become trapped in surrounding tissues, causing inflammatory immune responses and granuloma formation 1, 3
• The transmission cycle continues when eggs reach freshwater and hatch into miracidia that infect susceptible snail species 1

Clinical Manifestations

Acute Phase

• Initial infection may present with self-limiting hypersensitivity reactions known as Katayama fever 3
• This acute phase often goes unrecognized, especially in endemic areas 3

Chronic Phase

• Urogenital schistosomiasis (S. haematobium):

  • Characterized by dysuria and hematuria 3
  • Can lead to fibrosis and calcification in the lower urinary tract, causing obstruction, reflux, infection, and stone formation 4
  • Complications include renal failure and squamous cell carcinoma of the bladder 3, 4
  • May present with tubular dysfunction syndrome before progressing to end-stage renal disease 4

• Intestinal schistosomiasis (S. mansoni, S. japonicum):

  • Presents with abdominal pain and diarrhea, with or without blood 3
  • Complications include hepatic fibrosis, portal hypertension, splenomegaly, and variceal bleeding 3

• Other organ involvement:

  • CNS and respiratory tract can be affected in both forms 3
  • Glomerulonephritis may occur due to immune complex deposition containing worm antigens 4

Diagnosis

• Conventional diagnosis relies on detection of eggs in feces (S. mansoni, S. japonicum) or urine (S. haematobium), though sensitivity may be low, especially in low-prevalence areas 3, 5

• Traditional diagnostic approaches include:

  • Microscopic examination of excreta for parasite eggs 5
  • Detection of antibodies against schistosome antigens 5
  • Imaging techniques to assess organ damage 6

• Newer, more sensitive diagnostic methods include:

  • Detection of worm antigens in urine or serum, such as circulating cathodic antigen (CCA) and circulating anodic antigen (CAA) 5
  • Molecular techniques like PCR-based methods for genetic analysis 6
  • Mass spectrometry for detection of biological molecules 6

• Recent studies show that conventional diagnostic methods may significantly underestimate infection prevalence, with newer antigen detection tests revealing 6-10 times more infections in low-prevalence areas 5

Treatment and Management

• Praziquantel is the first-line treatment for all Schistosoma species, typically administered as a single oral dose of 40 mg/kg 7, 3
• For S. haematobium specifically, the American Journal of Kidney Diseases recommends praziquantel 40 mg/kg orally as a single dose, though dosage may vary based on clinical presentation 7
• Ensure sufficient dosage to completely eradicate the organism 7
• No immunosuppressive agents are indicated in schistosomal nephropathy 7
• While acute and early chronic lesions may regress with antiparasitic treatment, chronic sequelae are often irreversible 4
• End-stage renal disease requires dialysis and transplantation 4

Special Clinical Considerations

• Patients with elevated serum creatinine or hematuria should be evaluated for bladder cancer and urinary obstruction, which are common complications of S. haematobium infection 7
• Monitor patients with hepatic fibrosis from schistosomiasis for the development of kidney disease 7
• Test for endemic coinfections such as Salmonella, HBV, HCV, and HIV, as targeted treatment of these may alter the course of schistosomiasis complications 7
• Be aware that serology may remain positive for years after successful treatment and cannot be used to assess treatment success 7

Public Health Implications

• Schistosomiasis elimination requires a multifaceted approach including treatment, snail control, education, improved water and sanitation, accurate diagnostics, and surveillance systems 1
• Mass drug administration campaigns with praziquantel are widely implemented in endemic areas 3
• The discovery that schistosomiasis is more prevalent than previously thought (using newer diagnostic methods) has significant implications for public health goals and elimination strategies 5
• The existence of "egg-negative/worm-positive schistosomiasis" presents challenges for elimination programs, as these individuals may still contribute to transmission 5