Case Study: Schistosomiasis

Dr. Jennifer Coetzee

CMID / Ampath

Clinical Presentation

• 8 year old boy

• Referred to renal clinic from peripheral hospital

• Two year history of painless, macroscopic hematuria

• Urine microscopy: eggs of Schistosoma haematobium

Objectives

• Describe the life cycle of the bilharzia parasite

• Discuss the pathogenesis of bilharzia as a prototype of a parasitic infection

• Briefly describe the principles of the diagnosis and management of this infection

Ross A et al. N Engl J Med 2002;346:1212-1220

Life Cycle of the SchistosomeLife Cycle of the Bilharzia Parasite

Pathophysiology and Clinical Disease

• Acute disease:– Cercarial dermatitis after penetration of the

cercaria– “Swimmers itch” if cercaria from birds involved– After onset of egg laying, may develop acute

reaction (Katayama fever) if never exposed before

– Symptoms resolve as immune system adapts

Chronic Stages

• Eggs entrapped in host tissues secrete antigens

• Incite an inflammatory granulomatous response

• Granulomas eventually replaced by dense fibrosis obstruct blood flow

• Clinical symptoms vary according to species, total worm burden, patient’s stage of health at time of infection

Gastrointestinal Complications

• Wall of distal colon damaged as eggs pass through, become lodged

• Inflammatory response can cause focal ulcers or polyps

• May develop diarrhoea, abdominal pain or colitis

• ?Predisposing factor for colorectal carcinoma

Hepatosplenic Complications

• Eggs may incite granulomatous response in liver

• May become walled off with dense layers of fibrous tissue

• Pipestem fibrosis - obstructs portal veins

• Leads to portal hypertension, oesophageal varices, splenomegaly

Genitourinary Complications

• Eggs lodged in bladder wall - inflammatory infiltrate around the egg

• Overlying bladder epithelium hyperplastic, polyps

• Polyps erode, ulcerate - cause hematuria

• Log standing and severe infections may lead to carcinoma

• Fibrosis may lead to ureteric stricturing, hydronephrosis

Ross A et al. N Engl J Med 2002;346:1212-1220

Clinical Findings in Two Patients Infected with Schistosoma Species

Other Complications

• Cardiopulmonary Complications:– Eggs from shunted portosystemic blood lodged

in pulmonary arterioles– Granuloma formation, pulmonary hypertension,

cor pulmonale

• Central nervous system:– Eggs deposited in spinal column transverse

myelitis-like syndrome

Laboratory Diagnosis• Microscopy

– Detection of eggs in wet mounts of stool or urine– S. manoni has a lateral spine, S. haematobium has a

terminal spine

• Rectal or bladder biopsies may be necessary• Also antigen and antibody detection

– Antibodies cross react with other helminth infections– Problematic in endemic areas

Kaplan B and Meyers K. N Engl J Med 2000;343:1085

An eight-year-old boy was referred to the nephrology clinic with a two-year history of painless, gross macroscopic hematuria

Management and Prevention

• Anti-schistosomal drugs– Praziquantel

• Symptomatic management of complications

• Chemoprophylaxis available

• Vaccines under development

• Snail control!

Bibliography

• Ross A.G.P., Bartley P.B. et al. Schistosomiasis. New Eng J Med 2002; 346(16): 1212-1219

• Coon D.R. Schistosomiasis: Overview of the history, biology, clinicopathology, and laboratory diagosis. Clin Micro Newsletter 27(21): 163-169