Cysticercosis is a tissue infection caused by the metacestode (larval stage) of Taenia solium.
It is acquired through the accidental ingestion of T. solium eggs.
The disease is endemic in many parts of the developing world, including Latin America, Asia, and sub-Saharan Africa.
Cysticercosis is the most common intra-orbital parasitic infection.
It is observed in 13–46% of infected individuals.
The larvae of T. solium enter tissues such as muscle and brain, where they form cysts known as cysticerci.
Clinical manifestations
The incubation period of cysticercosis is variable; infected individuals may remain asymptomatic for up to a year.
Symptoms can appear months to years after the initial infection, typically when the cysts begin to die.
When the cysts die, the surrounding brain or other tissues may swell, causing symptoms.
Clinical effects vary based on the site of larval lodging, the number of larvae (larval burden), and the host’s immune response.
Clinical features are dependent on the specific site affected by the cysts.
a. Subcutaneous cysticercosis
Subcutaneous cysticercosis presents as small, movable, painless nodules.
These nodules are commonly observed in the arms or chest.
After a few months or even years, the nodules may become swollen, tender, and inflamed.
Eventually, the nodules gradually disappear.
b. Muscular cysticercosis
Muscular cysticercosis appears as dot-shaped or ellipsoidal calcifications.
Three types of clinical manifestations have been described in muscular cysticercosis, depending on the pathogenesis:
The myalgic type, which presents with muscle pain.
The mass-like, pseudotumor, or abscess-like type, which resembles a tumor or abscess.
The rare pseudohypertrophic type, characterized by abnormal muscle enlargement.
c. Neurocysticercosis
Neurocysticercosis is the most common and serious form of cysticercosis, occurring in the brain due to mass effects and inflammation caused by the degeneration of cysticerci and the release of antigens.
It is endemic in most Latin American countries, sub-Saharan Africa, and large regions of Asia, including the Indian subcontinent, most of Southeast Asia, and China.
Neurocysticercosis is observed in 60–90% of infected patients.
Brain cysts typically range from 4–20 mm in length, with most averaging between 8–10 mm.
Seizures and headaches are the most common symptoms, occurring in 70–90% of affected individuals.
Other symptoms include dizziness, involuntary muscle movements, intracranial hypertension, dementia, hydrocephalus (excess fluid around the brain), psychiatric disturbances, meningoencephalitis, transient paresis, behavioral disorders, aphasia, and visual disturbances.
It is considered the second most common cause of intracranial space-occupying lesions (ICSOL) in India, after tuberculosis.
Brain cysts are responsible for the most morbidity, with the brain being the most common site of cyst localization (seen in 60–90% of all cases).
d. Ocular cysticercosis
Ocular cysticercosis is present in approximately 20% of cases.
In this condition, cysts are located in the vitreous humor, subretinal space, and conjunctiva.
It may present as blurred vision or loss of vision, iritis, uveitis, and palpebral conjunctivitis.
In severe cases, the infection can lead to complete detachment of the retina.
Laboratory diagnosis
Diagnosis of cysticercosis is often challenging due to the nonspecific nature of its symptoms.
Proper diagnosis typically relies on a combination of clinical findings, serological tests, and epidemiological data.
1. Microscopy
Sample: Biopsy
Definitive diagnosis of cysticercosis is made by biopsy of the lesion followed by microscopic examination.
Microscopy reveals the presence of an invaginated scolex with suckers and hooks.
2. Imaging Methods
a. X-ray
Calcified cysticerci can be detected by radiography of subcutaneous tissues and muscles, especially in the buttocks and thigh.
Skull X-rays may reveal cerebral calcified cysts and intracranial lesions in cases of neurocysticercosis.
b. Computed tomography (CT)
CT scan of the brain is the best method for detecting dead, calcified cysts.
Cysticercal lesions appear as small hypodense areas (ring- or disc-like) with a bright central spot.
c. Magnetic resonance imaging (MRI)
MRI scan of the brain is more effective for detecting noncalcified cysts and ventricular cysts.
MRI also helps visualize spinal cysticerci.
However, the high costs of these radiologic methods significantly limit their availability and accessibility in most underdeveloped countries where cysticercosis is endemic.
3. Serology
a. Antibody detection
Samples: Cerebrospinal fluid (CSF) and serum
Anticysticercus antibodies in serum or CSF can be detected by ELISA and enzyme-linked immunoelectrotransfer blot (EITB) tests.
Native antigens: The EITB assay uses an affinity-purified lentil-lectin glycoprotein fraction (LLGP) as antigens and is considered the gold standard for neurocysticercosis serodiagnosis.
EITB has a sensitivity of 90% and specificity of 50–70%.
However, EITB is less effective at detecting antibodies when only a single cyst is present.
ELISA is less sensitive but technically simpler, making it widely used in clinical settings.
b. Antigen detection
Samples: Cerebrospinal fluid (CSF) and serum
Antigens can be detected in serum and CSF by ELISA using monoclonal antibodies.
The presence of antigens in serum or CSF indicates a recent or active infection.
Indirect immunofluorescence assay (IFA), which also uses monoclonal antibodies, is another method for antigen detection in neurocysticercosis.
4. DNA detection
Samples: Cerebrospinal fluid (CSF) and biopsy
PCR-based amplification methods are commonly used, targeting sequences such as repetitive DNA, ribosomal DNA, mitochondrial DNA, and the Antigen 2 (Ag2) gene.
Amplification of the pTsol9 repetitive sequence using conventional and real-time PCR, as well as seminested-HDP2-PCR, has been successfully applied for neurocysticercosis diagnosis.
These methods demonstrate high sensitivity and excellent specificity in identifying neurocysticercosis cases.
5. Others
Ocular cysticercosis can be diagnosed by ophthalmoscopy.
Eosinophilia often occurs in the early stages of cysticercosis but is not consistently present.
Elevated cerebrospinal fluid (CSF) protein levels are common in neurocysticercosis.
CSF may show lymphocytosis, with mononuclear pleocytosis frequently observed.
Glucose levels in CSF may be mildly to moderately low.
CSF cell counts rarely exceed 300 cells/mm³.
Treatments
Excision (surgical removal) is the best treatment method for cysticercosis whenever possible.
Asymptomatic neurocysticercosis typically requires no treatment.
For symptomatic cases, the two main anticysticercal drugs are praziquantel and albendazole.
Dosages:
Praziquantel: 50 mg/kg divided into 3 doses daily for 20–30 days.
Albendazole: 400 mg twice daily for 30 days.
Corticosteroids may be administered alongside praziquantel or albendazole to reduce inflammation caused by dying cysticerci.
Antiepileptic drugs should be given until brain inflammation subsides.
Surgical removal of cysts was the primary treatment before anticysticercal drugs but is now less favored due to its invasiveness and high risk of complications compared to chemotherapy.
Prophylaxis
Beef and pork intended for human consumption should undergo thorough inspection for cysticerci at slaughterhouses.
Avoid eating raw or undercooked beef and pork; cysticerci are killed by heating to 56°C for at least 5 minutes.
Maintain good personal hygiene and general sanitation practices.
Vaccines targeting pigs may help control disease spread since pigs have a short lifespan (about one year), making short-term immunity sufficient.
Vaccinating pigs is often preferred over confiscation, benefiting local farmers.
The most effective vaccines use recombinant oncosphere antigens TSOL18 and TSOL45 expressed in E. coli, with TSOL18 providing over 99% protection in trials.
Current efforts focus on making these vaccines widely available and practically effective.
Combining recombinant vaccines in pigs with anticysticercal chemotherapy in humans is considered the most effective strategy to control or eradicate cysticercosis.
References
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Meena, D., Gupta, M., Jain, V. K., & Arya, R. K. (2016). Isolated intramuscular cysticercosis: Clinicopathological features, diagnosis, and management – A review. Journal of Clinical Orthopaedics and Trauma, 7(Suppl 2), 243–249. https://doi.org/10.1016/j.jcot.2016.06.016
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