Taenia solium - Cysticercosis and Taeniasis

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Contributor

Jackson

Adjunct Professor of Pathology and Biomedical Informatics, University of Utah

Medical Director, Business Development, ARUP Laboratories

Cysticercosis and taeniasis are parasitic infections caused by the pork tapeworm Taenia solium during separate phases of its two-part life cycle. Cysticercosis results from infection of T. solium cystic larvae throughout the body (eg, in the muscular system); taeniasis, by contrast, is caused by adult T. solium tapeworms living within the intestinal tract. Taeniasis and muscular cysticercosis tend to be mild or asymptomatic, whereas cysticercosis infection within the central nervous system (CNS), known as neurocysticercosis (NCC), can involve serious or even life-threatening symptoms. Recommended testing methods vary depending on whether cysticercosis or taeniasis is suspected. Cysticercosis and NCC are typically diagnosed through a combination of serologic testing and CNS imaging. Taeniasis can be detected through stool microscopy.

Quick Answers for Clinicians

How are cysticercosis and taeniasis transmitted, and who is at risk of infection?

Cysticercosis (infection by T. solium cystic larvae) develops within the muscular system or central nervous system (CNS) following the accidental fecal-oral transmission of ova, whereas taeniasis (intestinal infection by adult-stage T. solium) occurs when undercooked meat containing cystic larvae is consumed. Individuals at risk of infection include those who have lived or extensively traveled in endemic areas (eg, developing regions where humans have close contact with host animals). Notably, individuals with taeniasis and those who have had close contact with taeniasis-infected individuals are also at risk of developing cysticercosis, as tapeworm ova are shed in their stool and can lead to infection. Although rare, transmission is possible in nonendemic areas.

What are the signs and symptoms of cysticercosis, and when is testing appropriate?

The symptoms of cysticercosis infection vary depending on the location, size, stage, and quantity of the encysted larvae (cysticerci) present. Infection in most locations of the body causes few or no symptoms, whereas individuals with neurocysticercosis (NCC) may experience seizures (present in up to 90% of symptomatic cases), intracranial hypertension, chronic meningitis, hydrocephalus, and other neurologic manifestations. Testing for cysticercosis is appropriate in symptomatic individuals when other common etiologies (eg, vasculitis, primary brain tumors, etc.) have been ruled out. Testing may also be appropriate in individuals diagnosed with taeniasis and members of their household when clinical assessment reveals signs that point to cysticercosis.

Why is a combined testing approach recommended to confirm suspected cysticercosis?

Because laboratory testing and central nervous system (CNS) imaging vary in diagnostic utility depending on an infection’s characteristics (eg, location, size, stage, and larva quantity), a combined testing approach for cysticercosis, including neurocysticercosis, is recommended to confirm infection and inform treatment strategy. For example, when infection is not extensive, serology may yield a false-negative result, whereas CNS imaging may indicate the need for treatment. Positive serology with negative imaging is also possible.

Are there any specific diagnostic criteria for neurocysticercosis?

Yes. To help increase the probability of an accurate diagnosis of neurocysticercosis (NCC), a panel of neurologic and infectious disease experts has released a list of stratified criteria for NCC diagnosis. These criteria also include an interpretive framework for defining diagnoses as definitive or probable. For specific information, refer to the Revised diagnostic criteria for neurocysticercosis.

Indications for Testing

Laboratory testing for cysticercosis is indicated in symptomatic individuals who are considered at risk when other common etiologies have been ruled out. Testing for taeniasis is indicated in at-risk individuals who report a history of expelling proglottids. In light of a cysticercosis or taeniasis diagnosis, subsequent testing for concurrent T. solium infections may also be indicated.

Laboratory Testing

When suspicion of cysticercosis (including NCC) exists, noncontrast computed tomography (CT) and magnetic resonance imaging (MRI) of the CNS should be followed up with confirmatory serologic testing. Notably, the CDC recommends the use of serology even when imaging does not identify the presence of cysticerci in the CNS, given that infection may be present elsewhere in the body.

For those with suspected taeniasis, intestinal infection can be identified through stool microscopy. Additional methods to detect taeniasis (ie, coproantigen, nucleic acid-based, and serologic testing) are currently only available on a research basis.

Subsequent testing via serology and/or stool microscopy is recommended in diagnosed individuals and members of their household to identify other possible T. solium infections that may be present. The following table summarizes the recommended additional testing for individuals diagnosed with cysticercosis and taeniasis.

Subsequent Laboratory Testing
Diagnosis	Additional Testing
Cysticercosis	Test patient and household for taeniasis via stool microscopy
Taeniasis	Clinically assess patient and household for cysticercosis; consider imaging and serology when signs and symptoms suggest the possibility of cysticercosis
References: Zammarchi, 2017; CDC

Serology

The enzyme-linked immunoelectrotransfer blot (EITB, or Western blot) test is widely preferred to detect anticysticercal antibodies and can be performed using serum (considered more sensitive) or cerebrospinal fluid (CSF). EITB testing may be found on a limited basis through commercial laboratories and can also be ordered directly through the CDC. Where EITB is unavailable, an enzyme-linked immunosorbent assay (ELISA) can be used for antigen detection and antibody detection, although the latter application is subject to cross-reactivity with other helminth organisms (eg, Echinococcus and Schistosoma). Serologic testing may vary in sensitivity based on the characteristics of infection (eg, severity and viability); therefore, a negative result should not be interpreted as ruling out infection.

Stool Microscopy

Microscopic demonstration of ova and proglottids, typically within a fecal sample, is currently the only commercial means to diagnose taeniasis. Analysis of three fecal samples collected on separate days is recommended to increase testing sensitivity. Repeat testing may increase the probability of detecting minor infections.

Taeniasis can occur due to other Taenia species. Because T. solium diagnoses entail subsequent testing, species identification via stool microscopy is recommended when possible. Mature proglottid or scolex examination is the primary means of identifying T. solium; the microscopic detection of ova is insufficient to provide a species-specific diagnosis.