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Cestode Infections¶

Chapter 242 | Part 5: Infectious Diseases · Part 5 – Infectious Diseases: Parasitic · Chapter 242

Key Clinical Points¶

Neurocysticercosis diagnosis relies on imaging visualization of a scolex ('dot-in-hole') or specific serology (EITB); calcified lesions are inactive and do not require antiparasitic therapy.
Management of neurocysticercosis prioritizes seizure control and hydrocephalus management before initiating antiparasitic drugs to avoid worsening inflammation.
Echinococcosis treatment is guided by WHO imaging classification (CE1-CE5); PAIR (aspiration, instillation, reaspiration) is preferred for small liver cysts (CE1-CE3), while surgery is required for multilocular disease or complex cases (CE4-CE5).
Paragonimiasis mimics tuberculosis; diagnosis requires detection of eggs in sputum/feces and a history of raw freshwater crab consumption.
Taenia solium eggs are immediately infective for humans; autoinfection can occur via ingestion of eggs from one's own feces.
Praziquantel is the drug of choice for Taeniasis and Paragonimiasis; Albendazole is the primary agent for Echinococcosis.
R. nana infection is unique among human cestodes as it does not require an intermediate host and causes autoinfection.
Echinococcal cyst rupture can cause anaphylaxis; aspiration should only be performed by experienced practitioners with precautions.
Diagnostic criteria for neurocysticercosis (Del Brutto) require one absolute criterion or specific combinations of major/minor neuroimaging and clinical/exposure criteria.
Prevention of Taenia solium infection involves adequate cooking of pork (56°C for 5 min) or freezing at -10°C for 9 days.

1. DEFINITION & OVERVIEW¶

Cestodes, or tapeworms, are members of the flatworm phylum (Platyhelminthes) and comprise the subphylum Cestoda.

Morphology & Habitat: ◦ Adult worms reside in the gastrointestinal tract of definitive hosts ◦ Larval forms are cystic and found in intermediate hosts
Clinical Significance: ◦ Human infections include both tapeworm (adult) and larval-stage parasites
Host Requirements: ◦ Taenia species require intermediate hosts for completion of life cycle ◦ Echinococcus spp. require both intermediate and definitive hosts ◦ R. nana is unique as it does not require an intermediate host ◦ Hymenolepis diminuta infects humans via contaminated food

1.1 Life Cycle Overview¶

Cycle Progression: ◦ Eggs are shed in feces → hatch to release oncospheres → penetrate intestinal mucosa ◦ Oncospheres migrate via bloodstream → form cysticerci in tissues ◦ Cysticerci may develop into adult tapeworms upon ingestion by definitive hosts ◦ Echinococcus larvae form hydatid cysts in intermediate hosts ◦ R. nana completes life cycle within human host
Cestode Life Cycle Stages (Table 1): ◦ Oncosphere: Intestinal lumen | Intermediate host ◦ Cysticercus: Muscle/viscera | Intermediate host ◦ Scolex: Intestinal mucosa | Definitive host ◦ Protoscolex: Hydatid cyst | Intermediate host

2. EPIDEMIOLOGY¶

Taenia saginata: Found globally where raw beef is consumed
T. solium: Endemic in Latin America, sub-Saharan Africa, and Southeast Asia
Echinococcus granulosus: Prevalent in Mediterranean, Middle East, and China
E. multilocularis: Found in Alpine regions and northern hemisphere
R. nana: Common in children with poor sanitation
H. diminuta: Rare human infection from contaminated food

2.1 Global Distribution¶

T. saginata: Sub-Saharan Africa, Middle East
T. solium: Latin America, India, China
E. granulosus: Mediterranean basin, Central Asia
E. multilocularis: Alpine regions, Arctic
Neotropical echinococcosis: Limited to South America

3. ETIOLOGY & PATHOPHYSIOLOGY¶

T. saginata: 8 m long with 1000-2000 proglottids
T. solium: 3 m long with 1000 proglottids, produces 50,000 eggs/proglottid
E. granulosus: Forms unilocular hydatid cysts with brood capsules
E. multilocularis: Creates multilocular alveolar lesions with invasive growth
R. nana: 2 cm adult worm with autoinfection cycle

3.1 Pathogenesis of Neurocysticercosis¶

Cysticerci in brain parenchyma: Cause seizures via inflammation
Subarachnoid cysts: Lead to hydrocephalus and arachnoiditis
Calcified lesions: Inactive; do not require treatment
Active lesions: Show enhancement on MRI/CT

4. CLINICAL FEATURES¶

Taeniasis: Asymptomatic or passage of proglottids in stool
Cysticercosis: Neurologic symptoms (seizures, hydrocephalus), ocular involvement, visceral manifestations
Echinococcosis: Abdominal mass, jaundice, pleural effusion, anaphylaxis on rupture

4.1 Neurocysticercosis Manifestations¶

Seizures: Most common presentation
Headache: With increased intracranial pressure
Hydrocephalus: Known as Bruns' syndrome
Meningitis/arachnoiditis: From subarachnoid cysts
Focal neurological deficits: From mass lesions

4.2 Echinococcosis Manifestations¶

Hepatic: Right upper quadrant pain, palpable mass
Pulmonary: Chronic cough, hemoptysis
Rupture: Anaphylaxis, urticaria, eosinophilia
Alveolar form: Slow-growing hepatic mass with progressive liver destruction

5. DIFFERENTIAL DIAGNOSIS¶

Neurocysticercosis: Distinguish from brain tumors, tuberculomas, toxoplasmosis
Echinococcosis: Differentiate from hepatic cysts, metastases
Paragonimiasis: Mimics tuberculosis and lung cancer
Taeniasis: Distinguish from other intestinal tapeworm infections

6. INVESTIGATIONS & DIAGNOSIS¶

Stool examination: For eggs/proglottids (Note: limited sensitivity)
Serology: EITB >99% specific for T. solium
Neuroimaging: MRI preferred for detecting scolex and enhancement
Diagnostic criteria: Del Brutto criteria with absolute/major/minor neuroimaging and clinical/exposure categories

6.1 Neurocysticercosis Diagnostic Criteria (Del Brutto)¶

Absolute criteria: ◦ Histologic demonstration of the parasite from biopsy of a brain or spinal cord lesion ◦ Visualization of subretinal cysticercus ◦ Conclusive demonstration of a scolex with a cystic lesion on neuroimaging studies
Neuroimaging criteria: ◦ Major: Cystic lesions without a discernible scolex, typical small enhancing lesions, multilobulated cystic lesions in the subarachnoid space, typical parenchymal brain calcifications ◦ Confirmative: Resolution of cystic lesions spontaneously or after cysticidal drug therapy; Migration of ventricular cysts documented on sequential neuroimaging studies ◦ Minor: Obstructive hydrocephalus or abnormal enhancement of basal leptomeninges
Clinical/exposure criteria: ◦ Major: Detection of specific anticysticercal antibodies (e.g., by EITB) or cysticercal antigens; Cysticercosis outside the central nervous system; Evidence of a household contact with T. solium infection ◦ Minor: Clinical manifestations suggestive of neurocysticercosis; Individuals coming from or living in an area where cysticercosis is endemic

6.2 Echinococcosis Imaging Classification (WHO)¶

Classification Basis: Based on number of cysts, presence of daughter cysts, and calcification.
CE1: Simple unilocular cyst without daughter cysts or calcification
CE2: Daughter cysts present but no calcification
CE3: Partially calcified cyst with daughter cysts
CE4: Completely calcified cyst with no daughter cysts
CE5: Multilocular, invasive lesion (alveolar form)

7. MANAGEMENT & TREATMENT¶

Neurocysticercosis Management:
Step 1: Seizure control with AEDs (e.g., Levetiracetam) before initiating antiparasitic therapy
Step 2: Corticosteroids (Dexamethasone 4-8 mg/day) to reduce inflammation
Step 3: Antiparasitic therapy (Albendazole 15 mg/kg BID for 14-30 days)
Step 4: Hydrocephalus management (Ventriculoperitoneal shunt if indicated)
Echinococcosis Management:
Step 1: Identify cyst type via WHO classification (CE1-CE5)
Step 2: For CE1-CE3 → Perform PAIR (Aspiration, instillation of scolicidal agents like 20% hypertonic saline, reaspiration) + Albendazole 10 mg/kg BID for 6 months
Step 3: For CE4-CE5 → Surgical resection + Albendazole 10 mg/kg BID for 6 months
Step 4: Ruptured cysts → Emergency surgical intervention + corticosteroids
Drug Therapy Summary:
Taeniasis: Praziquantel 25 mg/kg TID PO for 3 days
Neurocysticercosis: Albendazole 15 mg/kg BID PO for 14-30 days
Echinococcosis: Albendazole 10 mg/kg BID PO for 6 months
Paragonimiasis: Praziquantel 25 mg/kg TID PO for 28 days + corticosteroids

7.1 Neurocysticercosis Management¶

First-line: Albendazole 15 mg/kg BID for 14-30 days
Adjunctive: Dexamethasone 4-8 mg/day
Seizure control: Levetiracetam 50-1000 mg/day

7.2 Echinococcosis Management¶

PAIR Procedure: Aspiration, instillation of scolicidal agents (e.g., 20% hypertonic saline), reaspiration
Surgery: Required for CE4-CE5 or if PAIR fails
Post-procedure: Albendazole 10 mg/kg BID for 6 months

8. PROGNOSIS & COMPLICATIONS¶

Neurocysticercosis: Mortality 5-10% from status epilepticus or hydrocephalus
Echinococcosis: 10-year survival ≈ 70% with treatment; 30% without
Ruptured hydatid cysts: Anaphylaxis risk (20-40%) requiring emergency care

9. SPECIAL CONSIDERATIONS¶

Autoinfection: Occurs in Taenia solium and R. nana infections
Pregnancy: Avoid albendazole; use praziquantel for taeniasis
Immunocompromised patients: Higher risk of disseminated infection

10. KEY PEARLS & HIGH-YIELD POINTS¶

Neurocysticercosis: Scolex ('dot-in-hole') or EITB are key for diagnosis; calcified lesions do not need antiparasitics.
Echinococcosis: Management is driven by WHO CE1-CE5 classification; PAIR vs. Surgery.
Paragonimiasis: Look for lung symptoms + raw crab history + eggs in sputum/feces.
Taenia solium: High risk of autoinfection; prevention via cooking (56°C for 5 min) or freezing (-10°C for 9 days).
R. nana: Unique because it does not require an intermediate host.

Reference Tables¶

TABLE 242-1 Revised Diagnostic Criteria for Neurocysticercosis a 1. Absolute criteria¶

Harrison's 22e, p.1834

1. Absolute criteria
  a. Histologic demonstration of the parasite from biopsy of a brain or spinal
  cord lesion
  b. Visualization of subretinal cysticercus
  c. Conclusive demonstration of a scolex with a cystic lesion on neuroimaging
  studies
  2. Neuroimaging criteria
  a. Major neuroimaging criteria
  Cystic lesions without a discernible scolex, typical small enhancing
  lesions, multilobulated cystic lesions in the subarachnoid space, typical
  parenchymal brain calcifications
  b. Confirmative neuroimaging criteria
  Resolution of cystic lesions spontaneously or after cysticidal drug therapy
  Migration of ventricular cysts documented on sequential neuroimaging
  studies
  c. Minor neuroimaging criteria
  Obstructive hydrocephalus or abnormal enhancement of basal
  leptomeninges
  3. Clinical/exposure criteria
  a. Major clinical/exposure criteria
  Detection of specific anticysticercal antibodies (e.g., by enzyme-linked
  immunoelectrotransfer blot [EITB]) or cysticercal antigens by well-
  standardized immunodiagnostic tests
  Cysticercosis outside the central nervous system
  Evidence of a household contact with T. solium infection
  b. Minor clinical/exposure criteria
  Clinical manifestations suggestive of neurocysticercosis
  Individuals coming from or living in an area where cysticercosis is endemic