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Cysticercosis is caused by infection with the larval form (or cysticercus) of the tapeworm Taenia solium. The most important clinical manifestations are caused by cysts in the central nervous system, known as neurocysticercosis. The resulting signs and symptoms depend on the number, location, size, and stage (viable, degenerating, or calcified) of the cysticerci and the intensity of the host inflammatory response to degenerating cysts. Seizures are the most common manifestation, present in 70-90% of symptomatic patients in published case series. Less frequent clinical manifestations include intracranial hypertension, hydrocephalus, chronic meningitis, and cranial nerve abnormalities. Diagnosis usually involves both serological testing and brain imaging. The most urgent therapeutic interventions are aimed at managing the neurological complications, and may require anticonvulsant therapy, corticosteroids, neurosurgical intervention and/or treatment of increased intracranial pressure. Anthelminthic treatment may be indicated, but must be administered with caution, because larval death provokes an inflammatory response that may increase symptoms. Concomitant steroids are usually indicated.
The period between initial infection and symptom onset varies from several months to many years. In the United States, infections are detected predominantly in immigrants from Mexico, Guatemala, and other Latin American countries who acquired their infections in their home country. However, taeniasis and cysticercosis occur globally, with the highest rates in areas of Latin America, Asia, and sub-Saharan Africa with poor sanitation and free-ranging pigs with access to human feces.
Clusters and sporadic cases of cysticercosis acquired in the U.S. have been reported. Food handlers with taeniasis are of particular concern in this scenario (see prevention/control section for more information).
In humans, cysticerci (encysted larvae) often occur in skeletal muscles. However, the manifestations that most frequently lead patients to visit health care providers are caused by cysts in the central nervous system (CNS), known as neurocysticercosis. Less frequently, cysticerci may localize in the eyes, skin, or heart.
Neurocysticercosis may be parenchymal (occurring in the brain substance, the most common location) or extraparenchymal (occurring in the meninges, the ventricles, the basilar cisterns, or the subarachnoid space of the brain or spinal cord).
Clinical manifestations of cysticercosis depend on the number, location, size, and stage (viable, degenerating, or calcified) of the cysticerci and the intensity of the inflammatory response to degenerating cysts. Epilepsy is the most common manifestation, present in 70-90% of symptomatic patients in published case series. Less frequent clinical manifestations include intracranial hypertension, hydrocephalus, chronic meningitis, and cranial nerve abnormalities.
The number of cysticerci in the host can vary from one to more than 1,000. In the absence of massive numbers of cysticerci, the initial host tissue reaction is usually minimal. The developing cysticercus affects the surrounding tissue as a slowly growing mass that may cause pressure atrophy. Most live cysts do not cause an inflammatory reaction, but an acute inflammatory response occurs when the cysts degenerate, which results in the release of parasite antigens. Degeneration of a cyst may occur years after the initial infection. Some calcified cysts may intermittently release antigen, though this process is not fully understood. In the CNS, the inflammatory reaction and resultant edema appear as a contrast-enhancing ring around the cyst on imaging. There may be CSF pleocytosis as well. Necrotic larvae are completely or partially resorbed, but may become calcified, resulting in focal scarring that may provide a focus for seizures.
The distinction between parenchymal and extraparenchymal neurocysticercosis has important prognostic implications. Parenchymal disease with small numbers of cysts carries an excellent long-term prognosis (probably even without anthelminthic therapy) compared to parenchymal disease with > 50 cysts and extraparenchymal disease.
Diagnosis typically requires both CNS imaging and serological testing. A careful history should be taken, including questions regarding residence or extended travel in developing countries, and consumption of food prepared by someone who has lived in a high-risk area.
Diagnosis often requires both imaging and serological testing because:
- A patient may have clinical disease from a single or very few cysticerci. In this instance, serological results may be negative, but the lesions may be visible on imaging.
- A patient may have cysticerci in locations other than the brain. In this instance, CNS imaging is negative but serological results might be positive, indicating an antibody response to lesions elsewhere (e.g. the spinal cord).
- The location and characteristics of the lesions on imaging, especially on MRI, are essential to determine the best treatment modalities.
Computerized tomography (CT) is superior to magnetic resonance imaging (MRI) for demonstrating small calcifications. However, MRI shows cysts in some locations (cerebral convexity, ventricular ependyma) better than CT, is more sensitive than CT to demonstrate surrounding edema, and may show internal changes indicating the death of cysticerci.
In recent years, the use of CT and MRI has permitted identification of neurocysticercosis cases with a benign course that would not have been detected previously. It is now recognized that most infections are asymptomatic, or mildly symptomatic and benign. Mortality is low in patients with parenchymal cysts or calcification without hydrocephalus. However, untreated cysticercosis with hydrocephalus, large basilar or supratentorial cysts, massive numbers of cysts, intracranial hypertension, or cerebral infarction can be life-threatening.
There are two available serologic tests to detect cysticercosis, the enzyme-linked immunoelectrotransfer blot or EITB, and commercial enzyme-linked immunoassays. The immunoblot is the test preferred by CDC, because its sensitivity and specificity have been well characterized in published analyses.
At least one commercial laboratory offers EITB testing. For confirmatory testing in cases where EITB is not available, contact the CDC directly. Cysticercosis is a reportable disease in several states. Health care providers should check with their state health department to determine if they require notification of patients testing positive for cysticercosis.
The choice of treatment for neurocysticercosis depends on the clinical manifestations and the location, number, size, and stage of cysticerci. Anthelminthic chemotherapy for symptomatic neurocysticercosis is almost never a medical emergency. The focus of initial therapy is control of seizures, edema, intracranial hypertension, or hydrocephalus, when one of these conditions is present. Under certain circumstances, a ventricular shunt or other neurosurgical procedure may be indicated. Rarely, neurocysticercosis — especially large and/or subarachnoid (racemose) lesions — may present with imminent threat of intracranial herniation, a neurosurgical emergency.
Anthelminthic therapy, because it kills viable cysts and provokes an inflammatory response, may actually increase symptoms acutely. Co-administration of corticosteroids that cross the blood brain barrier (e.g. dexamethasone) is used to mitigate these effects. Recent placebo-controlled trials confirm that albendazole treatment in appropriately selected neurocysticercosis patients is effective in decreasing the frequency of generalized seizures in long-term follow-up.
Although the heterogeneity of the clinical picture of neurocysticercosis requires individual tailoring of treatment and management, several general principles apply:
- Anthelminthic therapy is generally indicated for symptomatic patients with multiple, live (noncalcified) cysticerci.
- Anthelminthic treatment will not benefit patients with dead worms (calcified cysts).
- Concomitant administration of steroids (e.g. dexamethasone) is often indicated to suppress the inflammatory response induced by destruction of live cysticerci.
- Conventional anticonvulsant therapy is the mainstay of management of neurocysticercosis-associated seizure disorders.
- Intraventricular cysts should usually be treated by surgical removal (endoscopic if possible). Anthelminthics are relatively contraindicated, because the resulting inflammatory response could precipitate obstructive hydrocephalus.
- Although our understanding of subarachnoid neurocysticercosis is evolving, treatment with both anthelminthics and corticosteroids is usually required. Ventricular shunting is often necessary as well.
Even when anthelminthic therapy is successful, continued use of anticonvulsant and other symptomatic medications may still be needed because the pathology may be irreversible. Decisions regarding discontinuation of anticonvulsant regimens must be made on an individual clinical basis, but data suggest that many patients can be eventually weaned from anticonvulsant therapy.
Several studies suggest that albendazole (conventional dosage 15 mg/kg/day in 2 divided doses for 15 days) may be superior to praziquantel (50 mg/kg/day for 15 days) for the treatment of neurocysticercosis. In comparative clinical trials, albendazole was equivalent or superior to praziquantel in reducing the number of live cysticerci. A recent placebo-controlled, double-blinded trial demonstrated that albendazole treatment (400 mg twice daily plus 6 mg dexamethasone QD for 10 days) significantly decreased generalized seizures over 30 months of follow-up.
More prolonged treatment courses (e.g. 30 days of albendazole, which may be repeated) may be needed for extraparenchymal or extensive disease. Albendazole is more likely to be effective against extraparenchymal forms of the disease because of better penetration than praziquantel into the CSF. Another possible contributing factor to the greater efficacy of albendazole is that serum and CSF metabolite levels appear to be potentiated by concomitant corticosteroids, whereas praziquantel levels are depressed. Albendazole, unlike praziquantel, has been reported to be effective in giant subarachnoid cysticerci (racemose cysts) and in extraocular muscle cysts. Both drugs appear to have a role in therapy, since cases that have not responded to one of the drugs have been reported to respond to the other.
Note on Treatment in Pregnancy
Albendazole is pregnancy category C. Data on the use of albendazole in pregnant women are limited, though the available evidence suggests no difference in congenital abnormalities in the children of women who were accidentally treated with albendazole during mass prevention campaigns compared with those who were not. In mass prevention campaigns for which the World Health Organization (WHO) has determined that the benefit of treatment outweighs the risk, WHO allows use of albendazole in the 2nd and 3rd trimesters of pregnancy. However, the risk of treatment in pregnant women who are known to have an infection needs to be balanced with the risk of disease progression in the absence of treatment.
Pregnancy Category C: Either studies in animals have revealed adverse effects on the fetus (teratogenic or embryocidal, or other) and there are no controlled studies in women or studies in women and animals are not available. Drugs should be given only if the potential benefit justifies the potential risk to the fetus.
Note on Treatment During Lactation
It is not known whether albendazole is excreted in human milk. Albendazole should be used with caution in breastfeeding women.
Note on Treatment in Pediatric Patients
The safety of albendazole in children less than 6 years old is not certain. Studies of the use of albendazole in children as young as one year old suggest that its use is safe. According to WHO guidelines for mass prevention campaigns, albendazole can be used in children as young as 1 year old. Many children less than 6 years old have been treated in these campaigns with albendazole, albeit at a reduced dose.
Oral praziquantel is available for human use in the United States.
Note on Treatment in Pregnancy
Praziquantel is pregnancy category B. There are no adequate and well-controlled studies in pregnant women. However, the available evidence suggests no difference in adverse birth outcomes in the children of women who were accidentally treated with praziquantel during mass prevention campaigns compared with those who were not. In mass prevention campaigns for which the World Health Organization (WHO) has determined that the benefit of treatment outweighs the risk, WHO encourages the use of praziquantel in any stage of pregnancy. For individual patients in clinical settings, the risk of treatment in pregnant women who are known to have an infection needs to be balanced with the risk of disease progression in the absence of treatment.
Pregnancy Category B: Either animal-reproduction studies have not demonstrated a fetal risk but there are no controlled studies in pregnant women or animal-reproduction studies have shown an adverse effect (other than a decrease in fertility) that was not confirmed in controlled studies in women in the first trimester (and there is no evidence of a risk in later trimesters).
Note on Treatment During Lactation
Praziquantel is excreted in low concentrations in human milk. According to WHO guidelines for mass prevention campaigns, the use of praziquantel during lactation is encouraged. For individual patients in clinical settings, praziquantel should be used in breast-feeding women only when the risk to the infant is outweighed by the risk of disease progress in the mother in the absence of treatment.
Note on Treatment in Pediatric Patients
The safety of praziquantel in children aged less than 4 years has not been established. Many children younger than 4 years old have been treated without reported adverse effects in mass prevention campaigns and in studies of schistosomiasis. For individual patients in clinical settings, the risk of treatment of children younger than 4 years old who are known to have an infection needs to be balanced with the risk of disease progression in the absence of treatment.
Prevention & Control
The control and prevention of cysticercosis depends on preventing fecal-oral transmission of eggs from persons with taeniasis. Follow-up of cysticercosis cases reported to the Los Angeles County Health Department from 1988 to 1991 demonstrated at least one active tapeworm carrier among family contacts of 22% of locally acquired cases, and 5% of imported cases. Identification and treatment of tapeworm carriers is an important public health measure that can prevent further cases.
When traveling to areas with poor sanitation, persons should be particularly careful to avoid foods that might be contaminated by human feces. Food handlers should be educated in good handwashing practices. Based on investigations of cases of neurocysticercosis in U.S. citizens who acquired their infections from asymptomatic household employees from Latin America, CDC recommended that such employees should have stool examinations for taeniasis and be treated if found to be infected. CDC does not recommend the routine testing of commercial food handlers, but does support policies aimed at ensuring that food handlers are taught and adhere to good handwashing practices.