Taenia solium

Background

Microbiology

• Cestode (tapeworm)
• Scolex (head) attached to strobila (body), which is composed of proglottids
  • Each proglottid contains male and female sexual organs
  • Each proglottid fills itself with eggs, then detaches, breaking down and releasing eggs
  • The proglottids are not motile, unlike T. saginata
• Can grow up to 2 to 8 m in length

Life Cycle

• Definitive host (e.g. humans) ingests meat (usually undercooked pork) containing viable cysts
  • The cysts develop into the tapeworms, releasing embryonated eggs into the environment
  • The tapeworms can live for 10 to 20 years
• Intermediate host (e.g. humans or pigs) ingests eggs in fecally-contaminated food
  • The egg invades into the organism, disseminates hematogenously, and forms a cyst in tissue
• Unique to T. solium is that humans can be both definitive and intermediate hosts
  • The human can become infected by autoinnoculation

Pathophysiology

• The adult tapeworms are very well tolerated, though they can decrease gut absorption

Epidemiology

• Common in Mexico, Central America, South America, the Philippines, and Southeast Asia
  • ~20-25% of randomly-selected people with have calcifications or serology consistent
• Neurocysticercosis causes ~50,000 deaths annually worldwide
  • Also one of the leading causes of seizure worldwide
• Usually acquired abroad, but there are cases of local acquisition from within the household
• Risk factors for cysticercosis include:
  • Residence in endemic country
  • Increasing age
  • Frequent consumption of pork
  • Poor household hygiene

Clinical Presentation

• Can be infected with the tapeworm (i.e. as definitive host) or with the cysts (i.e. as intermediate host), or with both (~25% of infections)

Taeniasis

• No specific symptoms, though may cause some element of malnutrition
• Can become symptomatic if autoinnoculation occurs

Cysticercosis

• Cysts can go anywhere, with the most dangerous and symptomatic locations being the heart and the brain
• They will eventually die and calcify, but will still be seen on plain X-ray

Neurocysticercosis

• Incubation period is usually 3 to 5 years but can be up to 30 years
• Most commonly presents with seizure (70%) or intracranial hypertension
• Intraparenchymal cerebral cysts enlarge slowly, asymptomatic for years or decades until they begin to die, causing inflammation
  • They can leak, provoking inflammation with cerebritis and meningitis
  • These can lead to focal or generalized seizures, focal neurological deficits, intellectual impairment, psychiatric disorders, and hydrocephalus
• Intraventricular and basilar cysts present earlier
  • Obstruction of CSF or local meningeal irritation
  • Can cause cranial nerve or brainstem deficits
  • Racemose cysticercosis (aggressive basilar neurocysticercosis) occurs when cysts proliferate at the base of the brain, causing coma and death
• Cysticercotic encephalitis occurs when there is a massive infection of the brain parenchyma
• Intraparenchymal spinal cord lesions can become symptomatic early due to local effects, or more slowly if outside the cord itself
• Ophthalmologic cysticercosis

Cardiac cysticercosis

• Rare, but can cause heart failure and conduction abnormalities

Diagnosis

Taeniasis

• Stool O&P
  • Eggs are indistinguishable from T. saginata, so ideally needs a proglottid for diagnosis
  • If seen, consider looking for concommitant cysts

Cysticercosis

• No single diagnostic test, but rather a combination of epidemiology, clinical presentation, imaging, and supportive laboratory investigations
• CSF for neurocysticercosis shows lymphocytic or eosinophilic pleiocytosis, hypoglycorrhachia, and elevated protein
  • Can send lentil lectin glycoprotein Western blot (LLGP-WB) or antibody testing, but sensitivity is proportional to number of lesions
• Serology is available, with enzyme-linked immunotransfer blot
  • Sensitivity high, but only confirms previous exposure
  • Sensitivity low in cases of only one cyst
  • High turnaround time

Neuroimaging

• Imaging with both non-contrast CT and MRI
• Shows multiple enhancing and nonenhancing unilocular cysts
• Average of 7 to 10 per patient
• Appearance on MRI depends on stage of development
  • Vesicular cysticerci are small and rounded, without edema, and can have a pathognomonic eccentric hyperdense nodule (represents the scolex)
  • Early vesicular stage shows smooth, thin-walled cysts, rarely with edema and contrast enhancement, but with a scolex often present
    • Typically <2 cm in diameter
    • The mural nodule of the scolex is pathognomonic
  • In the colloidal-vesicular stage, as the cyst degenerates, pericystic edema and cyst wall enhancement are visible
  • In the granular nodular stage, edema and contrast enhancement persist, with the cyst isointense on T1 and iso- to hypointense on T2
  • In the quiescent or residual stage, only small calcified nodules without mass effect and usually without enhancement are seen
• Colloidal and granular cysticerci are il-defined, with surrounding edema
• Calcified cysts can be detected on CT as hyperdense nodules without contrast enhancement

Classification of Neurocysticercosis

Form	Imaging	Histopathology
Parenchymal
Non-viable, calcified	Nodular calcifications <20 mm in diameter with or without edema and/or contrast enhancement	Calcified granuloma with or without surrounding inflammation and/or gliosis
Single, small enhancing	Cystic or nodular enhancing lesion <2 cm in size	Single parenchymal parasite in the process of degeneration with surrounding inflammation and variable opacification or absence of the cyst fluid
Viable parenchymal	Vesicular lesions often with evidence of associated contrast enhancement and/or surrounding edema; scolex often visible on high-definition	Parasites with intact cyst wall, vesicular fluid and scolex, with variable inflammation suurounding the parasite sometimes invading cyst wall
Extraparenchymal
Intraventricular	Cysticerci within the ventricles, obstructive hydrocephalus or loculated hydrocephalus with disproportionate dilatation of the ventricles	Viable cysticercus cyst within the ventricle and/or obstructive hydrocephalus
Subarachnoid	Cysticerci in the Sylvian fissure, in the basilar cisterns, or interhemispheric spaces. Strokes or meningitis without discrete cysts.	Cysticerci in the subarach space with arachnoiditis and vasculitis. The cysticerci are often in clusters with proliferating memranges (racemose) and may lack scolex
Spinal	Cysticerci within spinal subarach space with or without inflammation/arachnoiditis. Intramedullary cysticerci within the spinal cord	Subarach cysticerci often with associated arachnoiditis. Intramedullary csticerci similar pathologically to parenchymal cysticerci

Diagnostic Criteria

1. Parenchymal neurocysticercosis
   • Definitive parenchymal neurocysticercosis, one of the following:
     1. Parenchymal cyst with pathological diagnosis
     2. Single or multiple active parenchymal cysts, with at least one cyst with scolex on CT or MRI
     3. Multiple parenchymal vesicles without scolex associated with at least one of the following:
        1. Seizures: focal or generalized tonic‐clonic
        2. Positive serum or CSF immunological test (ELISA, EITB)
     4. Any combination of the parenchymal cysticercus in different evolutive stages: vesicular with or without scolex, degenerative (colloidal or nodular), and calcified
   • Probable parenchymal neurocysticercosis, one of the following:
     1. Single parenchymal calcification or vesicle (without scolex) or degenerating cyst(s), establishing differential diagnoses with other etiologies, associated with at least two of the following:
        1. Seizures: focal or generalized tonic‐clonic
        2. Subcutaneous or muscle cysts location confirmed by biopsy
        3. Positive serum or CSF immunological test (ELISA, EITB)
        4. Plain X‐ray films showing “cigar‐shaped” calcifications
        5. Individual who lives or has lived in or has traveled frequently to endemic countries
     2. Multiple parenchymal calcifications in an individual who lives or has lived in or has traveled frequently to endemic countries and in whom clinical state excludes other etiologies of calcifications
2. Extraparenchymal neurocysticercosis (intraventricular/basal subarachnoid)
   • Definitive extraparenchymal neurocysticercosis, one of the following:
     1. Extraparenchymal cyst with pathological diagnosis
     2. One or more extraparenchymal cysts on MRI special sequences with scolex in at least one of them
     3. One or more extraparenchymal cysts on MRI special sequences without scolex associated with at least two of the following:
        1. Hydrocephalus
        2. Inflammatory CSF
        3. Positive CSF immunological test (ELISA, EITB)
        4. Presence of single or multiple calcifications or parenchymal vesicular or degenerative cyst
3. Definitive parenchymal and extraparenchymal neurocysticercosis
   • Combination of the above definitive parenchymal and definitive extraparenchymal criteria

Management

Adult Tapeworm

• Praziquantel 5 to 10 mg/kg once
  • Well-tolerated, cysticidal
• Niclosamide 2 g once
  • Not absorbed, stays in the gut, therefore only kills the adult worms
• Don't treat during pregnancy unless necessary

Cysticercosis

• Surgical resection and antihelminthic therapy both can be used
• Screen everyone for ophthalmologic cysticercosis before treatment

Neurocysticercosis

• Non-contrast CT (for calcifications) and MRI brain
• Screen for LTBI if likely to need long steroids
• Screen for Strongyloides if likely to need long steroids
• Fundoscopy prior to starting antihelminthic
• Screen household members

Intraparenchymal Lesions

• Indications
  • Treat if viable cysts
  • Don't treat if only calcified cysts
  • May not need treatment if they are from India (overall good prognosis)
• Antiparasitic
  • If 1-2 viable cysticerci: albendazole 15 mg/kg/day (max 1200 mg/day) divided bid for 10 to 14 days with food
    • 60% resolve spontaneously by 1-2 years
    • Medications may increase time to resolution, but will lower risk of seizure recurrence
  • If >2 viable cysticerci: albendazole 15 mg/kg/day plus praziquantel 50 mg/kg/day for 10 to 14 days
  • If only calcified cysticerci: supportive treatment only
  • If diffuse encephalitis: avoid treating
• Adjuncts
  • Adjunctive corticosteroids for all for 6-8 weeks then taper
    • Need to start at least 24 hours before starting antiparasitic
  • If refractory seizures, consider neurosurgery service
  • Antiepileptic medications, which may later be tapered
• Monitoring
  • Monitor liver enzymes and leukopenia if >14+ days
  • MRI every 6 months until resolution
  • Re-treat if parenchymal cysts persist for 6 months after initial treatment

Extraparenchymal and Intraventricular Lesions

• Neurosurgical removal with minimally-invasive neuroendoscopy for lateral and third ventricles, and possibly fourth ventricle
  • If unable to, may need VP shunt
• Corticosteroids perioperatively
• Antihelminthic therapy only necessary in those that cannot have surgical removal

Subarachnoid Lesions

• Screen with spinal MRI for concommitant spinal cysticercus
• Treat with antihelminthic until radiographic resolution on MRI (at least 2-3 months, can be more than a year)
  • Variable response with high rate of relapse
• Corticosteroids prior to antiparasitic drugs
• Consider methotrexate as steroid-sparing agent
• VP shunt preferred to neurosurgery

Spinal Lesions

• Consider steroids and antihelminthic, as well as surgical options

Ocular Lesions

• Surgical removal

Pregnancy

• Defer antihelminthic until after pregnancy, if possible

Prevention

• Mainly prevented by good sanitation, animal husbandry, and food preparation
• Cook meats thoroughly, or freeze them thoroughly

Further Reading

• Diagnosis and Treatment of Neurocysticercosis: 2017 Clinical Practice Guidelines by the IDSA and ASTMH. Clin Infect Dis. 2018;66(8):e49-e75.
• New diagnostic criteria for neurocysticercosis: Reliability and validity. Ann Neurol. 2016;80(3):434-442.