Taenia Solium - Cysticercosis

Cysticercosis is a parasitic infection caused by the pork tapeworm, Taenia solium.

Epidemiology

Incidence
- Endemic in Mexico, Central and South America
- Etiological agent in 10% of new onset seizures

Organism

Humans can be a definitive host (adult worm in intestine) or a dead-end intermediate host (cysticercosis)
Humans are incidental hosts by contact with contaminated water or undercooked pork
Form depends on site of infection
- Tapeworm in intestine
- Larval forms in tissues

Clinical Presentation

Initial infection often asymptomatic
- Can have rapid onset depending on number of cysts and body site affected
Symptoms begin when cyst dies and depend on where the cysts are located
Dying cyst releases antigenic material, triggering the host inflammatory response
- Neurocysticercosis (cysts in the brain) is associated with seizures, meningitis/encephalitis and obstructive hydrocephalus
- Stroke patients initially present with elevated intracranial pressure (ICP), seizures, headache, nausea or mental status changes
Ocular cysts
- Usually vitreous, can be subretinal
- Blurry or disturbed vision, swelling or retinal detachment

Treatment

Treatment is usually necessary
- CNS disease may require treatment for hydrocephalus

Indications for Testing

Requires high index of suspicion in nonendemic areas

Criteria for Diagnosis

Proposed diagnostic criteria for human cysticercosis
- Absolute criteria
  - Demonstration of cysticerci by histologic or microscopic examination of biopsy materials
  - Visualization of the parasite in the eye by funduscopy
  - Neuroradiologic demonstration of cystic lesions containing a characteristic scolex
- Major criteria
  - Neuroradiologic lesions suggestive of neurocysticercosis
  - Demonstration of antibodies to cysticerci in serum by enzyme-linked immunoelectrotransfer blot
  - Resolution of intracranial cystic lesions spontaneously or after therapy with albendazole or praziquantel alone
- Minor criteria
  - Lesions compatible with neurocysticercosis detected by neuroimaging studies
  - Clinical manifestations suggestive of neurocysticercosis
  - Demonstration of antibodies to cysticerci or cysticercal antigen in CSF by ELISA
  - Evidence of cysticercosis outside the CNS (eg, cigar-shaped soft-tissue calcifications)
- Epidemiologic criteria
  - Residence in a cysticercosis-endemic area
  - Frequent travel to a cysticercosis-endemic area
  - Household contact with an individual infected with Taenia solium
- Key for diagnostic interpretation
  - Confirmation
    - 1 absolute criteria
    - 2 major, 1 minor, and 1 epidemiologic criteria
  - Probable
    - 1 major and 2 minor
    - 1 major, 1 minor, and 1 epidemiologic
    - 3 minor and 1 epidemiologic

Laboratory Testing

Based on consensus criteria
- CSF antibody by ELISA with confirmation by Western blot
- Serology – limited diagnostic use as a stand-alone test
  - 65-98% sensitive; 67-100% specific; may be useful if used with imaging data

Imaging Studies

Diagnosis is most often made by MRI or CT brain scans, but serologic screening by ELISA and confirmation by Western blot show increased sensitivity in the diagnosis of cysticercosis
- CT scan 95% sensitivity and specificity but lower for ventricular or cisternal forms
  - Single or multiple rounded lesions of low density with a small hyperdense mural nodule representing the scolex (starry night appearance)
- MRI – more sensitive than CT but much more expensive

Differential Diagnosis

Vasculitis
- Behcet syndrome
- Wegener granulomatosus
Central nervous system tumor (brain tumor)
Seizure disorders (epilepsy)
Infection
- Mycobacterium tuberculosis (TB)
- Fungal
- Toxoplasma gondii
- Brain abscess
- Nocardia spp
- Encephalitis
- Meningitis
Autoimmune diseases
- Systemic lupus erythematosus
- Sjogren syndrome

Tests generally appear in the order most useful for common clinical situations

Test name: Cysticercosis Antibody, IgG by ELISA

ARUP #: 0055284

Methodology: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Use:

Detect presence of IgG antibodies to T. solium in serum when a clinical suspicion of cysticercosis exists

Limitations:

Most sensitive in disseminated disease

Follow-up:

CT or MRI suggested for neurologic presentations of the disease

Test name: Cysticercosis Antibody, IgG by Western Blot

ARUP #: 0055283

Methodology: Qualitative Western Blot

Use:

Confirm IgG antibodies to T. solium in serum or CSF

Confirm positive results from ELISA testing

Limitations:

Consider testing for contamination by blood or transfer of serum antibodies across the blood-brain barrier

Due to the cross-reactivity that exists between cysticercosis and echinococcus antibodies (approximately 23%) a positive result by ELISA should be confirmed by Western blot

Follow-up:

CT or MRI suggested for neurologic presentations of the disease

Test name: Cysticercosis Antibody, IgG by ELISA (CSF)

ARUP #: 0055285

Methodology: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Use:

Detect the presence of CSF IgG antibodies to T. solium, when a clinical suspicion of cysticercosis exists

Limitations:

Diagnosis of central nervous system infections can be accomplished by demonstrating the presence of intrathecally-produced specific antibody

Interpretation of results may be complicated by low antibody levels found in CSF, passive transfer of antibody from blood, and contamination via bloody taps

Follow-up:

CT or MRI suggested for neurologic presentations of the disease

Test name: Cysticercosis Antibody, IgG by Western Blot (CSF)

ARUP #: 0055282

Methodology: Qualitative Western Blot

Use:

Confirm IgG antibodies to T. solium in CSF

Confirm positive results from ELISA testing

Limitations:

Interpretation of results may be complicated by low antibody levels found in CSF, passive transfer of antibody from blood, and contamination via bloody taps

Follow-up:

CT or MRI suggested for neurologic presentations of the disease

General

Hill, Harry R., MD. Group Medical Director, Laboratory of Immunology, ARUP Laboratories, and Executive Director of the ARUP Institute for Clinical and Experimental Pathology; Professor and Division Head, Pathology (Clinical), University of Utah

Comprehensive Review: April 2011
Last Update: April 2011

Central Nervous System Tumors

Encephalitis, Infectious

Meningitis, Acute

Seizure Disorders