Schistosomiasis and OtherTrematode Infections¶
Chapter 241 | Part 5: Infectious Diseases · Part 5 – Infectious Diseases: Parasitic · Chapter 241
Key Clinical Points¶
- Schistosomiasis is a major neglected tropical disease, second only to malaria in public health impact.
- Diagnosis relies on egg detection (stool/urine/tissue), PCR for sensitivity, and serology.
- Praziquantel is the primary drug of choice for all human schistosome species.
- S. haematobium is a Group 1 carcinogen linked to bladder squamous cell carcinoma.
- Acute schistosomiasis (Katayama fever) occurs 2–3 months post-exposure and may require glucocorticoids.
- Dracunculiasis (Guinea worm) requires extraction as the sole treatment; it persists in animal reservoirs.
- Food-borne trematodes are zoonotic and acquired via ingestion of raw/undercooked aquatic food or plants.
- Triclabendazole is the drug of choice for Fasciola hepatica and F. gigantica infections.
- Neuroschistosomiasis can cause severe CNS complications like transverse myelitis.
- Climate change may expand snail habitats, potentially shifting the geography of infection.
DEFINITION & CLASSIFICATION¶
• Schistosomiasis: Parasitic disease caused by trematode worms of the genus Schistosoma. • Trematodes: Flatworms (phylum Platyhelminthes) characterized by: ◦ Macroscopic size (1–several cm) ◦ Dorsoventral flattening ◦ Bilateral symmetry with two suckers • Sexual Dimorphism: Unlike most other human parasitic trematodes (which are hermaphroditic), schistosomes have separate sexes. • Dracunculiasis: Caused by Dracunculus medinensis; a poverty-related chronic disease with high morbidity. • Food-borne Trematodes: Zoonotic infections acquired via ingestion of undercooked aquatic food or water plants.
Classification of Trematode Infections¶
• Categorization by Adult Worm Location: ◦ Blood: Schistosomes ◦ Liver: Clonorchis, Opisthorchis, Fasciola ◦ Intestine: Fasciolopsis, Echinostoma, Heterophyes ◦ Lungs: Paragonimus • Clinical Course: Adult worms do not multiply in mammalian hosts but can survive up to 30 years; infections are typically chronic.
EPIDEMIOLOGY¶
• Transmission Factors: Dependent on freshwater habitats for snail intermediate hosts, human activity, and climate. • Prevalence: Endemic in 78 countries; >70% of cases are in sub-Saharan Africa. • Demographics: Children typically acquire infection at ~3–4 years; prevalence peaks during puberty due to delayed immunity. • Impact of Climate Change: Rising temperatures and infrastructure projects (irrigation/hydroelectric) expand snail habitats, potentially shifting disease geography. • Dracunculiasis Status: Incidence has declined but persists in animal reservoirs (dogs/cats); 13 cases reported in 2022.
Risk Factors¶
• Environmental: Increasing temperatures → expanded snail habitats; large-scale irrigation/hydroelectric projects. ◦ Occupational: Water contact (fishermen, rice farmers). ◦ Social: Travel/migration patterns; poor sanitation and lack of safe water access.
ETIOLOGY & PATHOPHYSIOLOGY¶
• Infection Pathway: Cercarial penetration of skin in freshwater → transformation to schistosomula → circulation through lungs → maturation in mesenteric/pelvic veins. • Prepatent Period: 5–7 weeks; ends with egg production. • Pathology Mechanism: 50% of eggs remain in tissues → trigger immune responses (serum sickness-like reactions) → formation of granulomas (lymphocytes, eosinophils, activated macrophages). • Immune Response: Chronic infection leads to regulatory cytokine-mediated immunomodulation.
Life Cycle Details¶
• Dracunculiasis Cycle: Humans ingest water with Cyclops larvae → larvae penetrate GI tract → adult worms mate → female migrates to subcutaneous tissue → blister/ulcer forms → larva released in water → ingested by Cyclops.
Egg Morphology¶
• S. haematobium: 140 μm long with terminal spine. ◦ S. mansoni: 150 μm long with lateral spine. ◦ S. japonicum: ~90 μm, rounder with small lateral spine. ◦ Note: Eggs contain ciliated miracidia for tissue migration.
CLINICAL FEATURES¶
• Acute Schistosomiasis (Katayama fever): ◦ Onset: 2–3 months post-exposure. ◦ Symptoms: Fever, myalgia, fatigue, cough, abdominal pain, eosinophilia. ◦ Severe cases: Weight loss, dyspnea, hepatomegaly, or CNS involvement. • Urogenital Schistosomiasis (S. haematobium): ◦ Active stage: Terminal hematuria, dysuria, suprapubic pain. ◦ Chronic stage: 'Sandy patches' on cystoscopy, obstructive uropathy, hydronephrosis. ◦ Genital: Dyspareunia, hematospermia, perineal pain. • Hepatosplenic Schistosomiasis (S. mansoni/japonicum): ◦ Early phase: Hepatosplenomegaly, left hypochondrial mass. ◦ Late phase: Periportal fibrosis, portal hypertension, esophageal varices. ◦ Complications: Delayed growth, severe anemia, ascites.
Acute Schistosomiasis (Katayama Fever)¶
• Presentation: Sudden onset 2–3 months post-exposure in first-time travelers. ◦ Symptoms: Fever, myalgia, fatigue, headache, nonproductive cough, abdominal pain. ◦ Complications: Cerebral/spinal involvement, pulmonary hypertension, cor pulmonale.
Urogenital Schistosomiasis¶
• S. haematobium: ◦ Active (children/young adults): Painless terminal hematuria, dysuria. ◦ Chronic: Obstructive uropathy, hydronephrosis, 'sandy patches' on cystoscopy.
Hepatosplenic Schistosomiasis¶
• S. mansoni/japonicum: ◦ Early (children): Hepatosplenomegaly, left lobe liver enlargement. ◦ Late (adults): Periportal fibrosis, portal hypertension, esophageal varices.
DIFFERENTIAL DIAGNOSIS¶
• Acute Schistosomiasis must be differentiated from: ◦ Malaria, salmonellosis, acute hepatitis. ◦ Trichinosis, tropical eosinophilia, strongyloidiasis. ◦ Visceral larva migrans, Opisthorchis/Clonorchis infections.
DIAGNOSTIC APPROACH¶
- Egg Detection: Identify schistosome eggs in stool (S. mansoni/japonicum), urine (S. haematobium), or tissue biopsies.
- Molecular Testing: PCR for improved sensitivity and specific species identification.
- Serology: ELISA or Western blot for antibody detection.
- Imaging: Ultrasound to evaluate hepatosplenomegaly/fibrosis; cystoscopy to identify 'sandy patches'.
- Clinical Correlation: Match symptoms (e.g., terminal hematuria) with specific parasite types.
MANAGEMENT & TREATMENT¶
- Praziquantel (Drug of Choice for all Schistosomes): ◦ Dose: 40 mg/kg PO in 2 divided doses for 1 day. ◦ Indications: S. mansoni, S. haematobium, S. intercalatum, S. guineensis.
- Triclabendazole (Drug of Choice for Fasciolidae): ◦ Dose: 10 mg/kg PO twice daily for 2 days (for Fasciola infections). ◦ Alternative: 25 mg/kg PO tid for 2 consecutive days (for Clonorchis, Opisthorchis).
- Supportive Care: ◦ Glucocorticoids: Administer for severe acute cases (e.g., Katayama fever).
- Prevention & Control: ◦ Mass drug administration (MDA) in endemic areas. ◦ Snail control programs using molluscicides. ◦ Public health education on water safety and avoiding contaminated sources.
Pharmacologic Treatment Summary¶
• Praziquantel: 40 mg/kg PO (1 day) → Standard for all Schistosomes. ◦ Side effects: Nausea, dizziness. ◦ Note: Contraindicated in pregnancy (except S. haematobium). • Triclabendazole: 10 mg/kg PO (2 days) or 25 mg/kg tid (2 days) → For Fasciola, Clonorchis, Opisthorchis. ◦ Side effects: Nausea, abdominal pain; Contraindicated in pregnancy.
COMPLICATIONS & PROGNOSIS¶
• Urogenital (S. haematobium): ◦ Bladder squamous cell carcinoma (Group 1 carcinogen). ◦ Obstructive uropathy, hydronephrosis. • Hepatic (S. mansoni/japonicum): ◦ Periportal fibrosis, portal hypertension, esophageal varices, ascites. • Neurological: ◦ Neuroschistosomiasis: Transverse myelitis, encephalopathy, ataxia. • Pulmonary: ◦ Fibrosis, pulmonary hypertension, cor pulmonale.
Chronic Sequelae¶
• Urogenital: Squamous cell carcinoma, obstructive uropathy. • Hepatic: Periportal fibrosis, portal hypertension, ascites. • CNS: Neurologic deficits, seizures, myelitis. • Pulmonary: Interstitial fibrosis, cor pulmonale.
SPECIAL POPULATIONS¶
• Pediatric Considerations: ◦ Children have higher prevalence and earlier infection. ◦ 80% of infected children show hepatosplenomegaly. ◦ S. japonicum infections associated with delayed growth/puberty. ◦ Higher risk of severe acute disease in first-time exposures. • Zoonotic Considerations: ◦ Food-borne trematodes require animal reservoir control (e.g., dogs/cats for Dracunculiasis). ◦ Public health education on zoonotic transmission risks and food safety regulations.
KEY PEARLS & HIGH-YIELD POINTS¶
• Clinical Pearls: ◦ Katayama fever may mimic malaria or viral hepatitis. ◦ 'Sandy patches' on cystoscopy are pathognomonic for S. haematobium. ◦ Praziquantel is contraindicated in pregnancy (except for S. haematobium). • Common Pitfalls: ◦ Misdiagnosing urogenital symptoms as UTI or prostatitis. ◦ Underestimating the role of climate change in disease spread. ◦ Overlooking neurologic complications in travelers.
Reference Tables¶
TABLE 241-1 Major Human Trematode Infections TREMATODE Blood Flukes Intestinal schistosomiasis Schistosoma mansoni…¶
Harrison's 22e, p.1826
| TREMATODE | TRANSMISSION ROUTE | GEOGRAPHIC DISTRIBUTION |
|---|---|---|
| Blood Flukes | ||
| Intestinal schistosomiasis | ||
| Schistosoma mansoni |
Skin penetration by cercariae released from snails (Biomphalaria spp.) |
Africa, Brazil, Venezuela, Surinam, the Caribbean (low risk) |
| Shistosoma japonicum |
Skin penetration by cercariae released from snails (Oncomelania spp.) |
China, Indonesia, Philippines |
| Schistosoma guineensis and Schistosoma intercalatum |
Skin penetration by cercariae released from snails (Bulinus spp.) |
Rainforest areas of Central Africa |
| Schistosoma mekongi |
Skin penetration by cercariae released from snails (Neotricula aperta) |
Several districts of Cambodia and Lao People’s Democratic Republic (PDR) |
| Liver Flukes | ||
| Clonorchis sinensis | Ingestion of metacercariae in freshwater fish |
Asia, including Republic of Korea, China, Taiwan, Vietnam |
| Ingestion of metacercariae in freshwater fish |
||
| Opisthorchis felineus |
Ingestion of metacercariae in freshwater fish |
Former Soviet Union, Kazakhstan, Ukraine, Turkey |
| Ingestion of metacercariae on aquatic plants or in water |
||
| Fasciola gigantica | Ingestion of metacercariae on aquatic plants or in water |
Africa, Asia |
| Intestinal Flukes | ||
| Ingestion of metacercariae on aquatic plants |
||
| Echinostoma spp. | Ingestion of freshwater fish, frogs, mussels, snails |
China, India, Indonesia, Japan, Malaysia, Russia, Republic of Korea, Philippines, Thailand |
| Ingestion of metacercariae in freshwater or brackish- water fish |
||
| Lung Flukes | ||
| Paragonimus westermani |
Ingestion of metacercariae in crayfish or crabs |
Tropical and subtropical areas of eastern and southern Asia and sub-Saharan Africa |
| Ingestion of metacercariae in crayfish or crabs |
TABLE 241-2 Treatment of Schistosomiasis and Food-Borne Trematode Infections INFECTION Schistosoma mansoni, S.…¶
Harrison's 22e, p.1830
| INFECTION | DRUG OF CHOICE | ADULT DOSEa |
|---|---|---|
| Schistosoma mansoni, S. haematobium, S. intercalatum, S. guineensis |
Praziquantelb | 40 mg/kg PO in 2 divided doses for 1 day |
| Praziquantel | ||
| Clonorchis sinensis, Opisthorchis viverrini, Opisthorchis felineus |
Praziquantel | 25 mg/kg PO tid for 2 consecutive days |
| Triclabendazolec | ||
| Fasciolopsis buski | Praziquantel | 75 mg/kg PO in 3 divided doses for 1 day |
| Praziquantel | ||
| Paragonimus westermani, Paragonimus kellicotti |
Praziquantel Triclabendazolec |
25 mg/kg PO tid for 2 consecutive days 10 mg/kg PO once (or twice, 12–24 h apart) |
TABLE 241-3 Clinical Features of Food-Borne Trematode Infections INFECTION Liver Flukes Clonorchis sinensis…¶
Harrison's 22e, p.1831
| INFECTION | SYMPTOMS OR SIGNS | COMPLICATIONS | |
|---|---|---|---|
| EARLY OR ACUTE STAGE | ESTABLISHED OR CHRONIC STAGE | ||
| Liver Flukes | |||
| Clonorchis sinensis, Opisthorchis viverrini, Opisthorchis felineus |
Often asymptomatic; sometimes hepatitis-like symptoms and high fever (especially with O. felineus) |
Biliary colic, cholestatic jaundice, recurrent cholangitis and cholelithiasis; hepatomegaly, gallbladder enlargement, periductal fibrosis. Light infections are often asymptomatic and remain so for years. |
Pancreatitis, cholangiocarcinomaa |
| Acute onset (1–4 weeks after infection) with high fever, weight loss, sometimes urticaria and liver tenderness |
Biliary colic, cholestatic jaundice, recurrent cholangitis and cholelithiasis; thickening, enlargement, and fibrosis of biliary ducts; sometimes repeated relapses of acute symptoms |
||
| Intestinal Flukes | |||
| Fasciolopsis buski, Echinostoma spp., Heterophyes heterophyes, several other species |
Often asymptomatic; sometimes nonspecific gastrointestinal symptoms |
Heavy infection may lead to ulceration of intestinal mucosa and malabsorption. Mild infections are often asymptomatic. |
Malnutrition, anemia; rarely, ectopic infection in the central nervous system |
| Lung Flukes | |||
| Often asymptomatic; sometimes insidious onset with anorexia and weight loss |
Bronchitis-, asthma-, and tuberculosis-like symptoms and signs such as chronic cough, dyspnea, bloody (“rusty”) sputum |