Taenia solium (Pork Tapeworm)

Classification and Morphology

• Scolex (head): Four muscular cup-shaped suckers plus a rostellum with a double crown of hooklets (this distinguishes it from T. saginata, which has no hooks - hence T. solium = "armed" tapeworm)
• Adult worm length: 10-20 feet (some sources up to 30 feet)
• Proglottids: Terminal proglottids are ~2 cm long, 0.5-1 cm wide, 1-2 mm thick. Gravid proglottids contain fewer than 13 uterine branches (vs ≥14 in T. saginata) - key distinguishing feature
• Ova: 40 µm diameter, surrounded by brown radial striations, embryos with 6 hooks - morphologically identical to T. saginata eggs

Life Cycle

Route 1 - Taeniasis (Definitive Host)

1. Human ingests undercooked pork containing cysticerci (larval cysts)
2. Cysticercus evaginates in the small intestine, scolex attaches to intestinal wall
3. Proglottids form at base of scolex, mature into an adult tapeworm
4. Gravid proglottids and eggs are shed in stool
5. Pigs (intermediate host) ingest eggs from fecally contaminated environment
6. Eggs hatch → oncospheres penetrate pig gut wall → disseminate hematogenously → encyst in muscle as cysticerci

Route 2 - Cysticercosis (Accidental Intermediate Host)

1. Human ingests eggs (not larvae) from fecally contaminated food, water, or via autoinfection
2. Eggs hatch → oncospheres penetrate intestinal wall → hematogenous spread
3. Lodge in tissues (brain, muscle, subcutaneous tissue, eye) → develop into cysticerci
4. Critical: The egg-ingestion route does NOT require pork consumption - vegetarians and people who never eat pork can get cysticercosis from contact with a tapeworm carrier (e.g., infected household worker)

Epidemiology

• Endemic regions: Latin America, sub-Saharan Africa, South/Southeast Asia, Eastern Europe, China, India, Pakistan
• Correlates with poor sanitation, free-ranging pigs, and unregulated slaughter practices
• An estimated 370,000 symptomatic new cases of taeniasis/cysticercosis occurred in 2010, with >28,000 attributed deaths
• Leading cause of acquired epilepsy worldwide - WHO estimates 30% of epilepsy cases in endemic areas are attributable to cysticercosis
• Both conditions are WHO Neglected Tropical Diseases (NTDs)
• In the US, cases are mainly seen in immigrants from endemic countries, with rare autochthonous transmission

Disease Manifestations

1. Taeniasis (intestinal infection with adult worm)

• Usually asymptomatic or mild: nausea, abdominal discomfort, anorexia, pruritus ani
• Motile proglottids may be noted in stool or exiting the anus
• Far less clinically significant than cysticercosis

2. Cysticercosis / Neurocysticercosis (larval tissue infection)

• Viable (vesicular): thin translucent bladder with invaginated scolex, little inflammation
• Degenerating (colloidal): turbid fluid, surrounding edema and enhancement on MRI
• Granular: cyst collapses, granuloma forms
• Calcified: end-stage, may continue to cause perilesional edema and seizures

Diagnosis

Taeniasis

• Stool microscopy: identify ova (identical to T. saginata) or proglottids
• Proglottid morphology: count uterine branches to distinguish species (<13 = T. solium, ≥14 = T. saginata)

Cysticercosis / Neurocysticercosis

• Neuroimaging (CT/MRI): key modality - detects cystic lesions, scolex ("hole-with-dot" sign), calcifications, hydrocephalus, enhancement
• Serology: Enzyme-Linked Immunoelectrotransfer Blot (EITB) using lentil lectin-purified glycoproteins is >99% specific and sensitive for multiple cysts (less sensitive for single or calcified lesions). Crude antigen ELISAs have high false-positive/negative rates and should be avoided
• Biopsy: histologic demonstration of parasite (absolute criterion)
• Subcutaneous nodules: surgical removal and examination

Del Brutto Revised Diagnostic Criteria (2017) - Harrison's 22e

1. Histologic demonstration from brain/spinal cord biopsy
2. Visualization of subretinal cysticercus
3. Scolex within cystic lesion on neuroimaging

Treatment

Taeniasis

• Praziquantel 10 mg/kg single dose (drug of choice) - use with caution if comorbid cysticercosis suspected, as it can trigger CNS inflammation/seizures
• Niclosamide 2 g single dose - equally effective, safer in patients with occult cysticercosis

Neurocysticercosis - Principles

1. Stabilize first: antiseizure medications, manage raised ICP
2. Antiparasitic drugs are contraindicated in patients with elevated ICP or purely calcified lesions

• Single enhancing lesions: may taper ASMs after 6 months if imaging normalizes
• Multiple parenchymal lesions: taper after 2 years if lesions resolve, no calcification, no breakthrough seizures
• Calcified lesions: higher risk of recurrent seizures, especially with perilesional edema

• Ventricular cysts in lateral/3rd ventricle → neuroendoscopic removal (preferred)
• 4th ventricle → microdissection posterior approach or neuroendoscopy
• If complete removal impossible → ventriculoperitoneal (VP) shunting

• Albendazole 15 mg/kg/day for 8-28 days (preferred for parenchymal disease)
• Combination albendazole + praziquantel 50 mg/kg/day - more effective for >2 cystic lesions or subarachnoid disease
• Always co-administer glucocorticoids (dexamethasone 0.1-0.4 mg/kg/day or prednisone 60 mg/day) to limit inflammation from dying parasites

• Ocular cysticercosis: surgical management only (drugs risk irreversible inflammation)
• Subarachnoid/racemose NCC: prolonged antiparasitic + prolonged glucocorticoids + shunting for hydrocephalus; methotrexate or TNF inhibitors as steroid-sparing agents in refractory cases

Prevention and Control

• Taeniasis prevention: cook pork until interior is gray (56°C for 5 min) or freeze at -20°C for ≥7-10 days; meat inspection
• Cysticercosis prevention: handwashing, treated water, proper disposal of human feces; treat tapeworm carriers
• Programmatic control: mass chemotherapy in human and pig populations; porcine vaccine licensed in India (and a few other countries)

Key Distinguishing Points: T. solium vs T. saginata