Vol. 20, No. 46
THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER
Tuesday, November 13, 2001

A. Provided by Karen Fujii, MHS, Division of Outbreak Investigation, Maryland Department of Health and Mental Hygiene.

A 48 year old right-handed Ecuadorian woman presents with a history of seizures for the past 6 years. They are characterized by speech arrest and shaking of the left hand. Initially, the frequency was about three times per month, but have now increased to daily occurrences. Imaging revealed cystic calcification in the superior temporal gyrus. Craniotomy was performed, revealing foreign body giant cell reaction with calcification and degenerated material consistent with a cysticercus.

Introduction: Neurocysticercosis, infection of the central nervous system (CNS) by larvae of the pork tapeworm Taenia solium, is the most common neuroparasitic infection in humans. It has a worldwide distribution but is most common in Central and Latin America, Mexico, Asia, Africa, Spain, Portugal, and Eastern Europe. Most infected patients in industrialized nations are immigrants from endemic regions.

Organism and epidemiology. Humans are the only definitive hosts of the pork tapeworm Taenia solium. Infection is aquired by different routes. In the usual or benign life cycle, humans are infected by eating measly pork (pork which is infected by viable larvae or cysticerci). The ingested cysticerci attach to the jejunum where they mature into adult tapeworms. The tapeworm sheds gravid proglottids into the stool. If contaminated food is ingested by the pig then the eggs hatch, burrow through the pig's gastrointestinal tract, enter the circulation, and encyst in systemic tissue, including the brain, where they develop into the larval or cysticercus form. The life cycle is then complete, with the human acting as definitive host and the pig as intermediate host. Humans, however, may become accidental intermediate hosts by ingesting products which are fecally contaminated with T. solium eggs, either shed in a food handler's feces or in their own feces if they are infected by the adult tapeworm. If the resulting larvae encyst in the brain, neurocysticercosis develops. Cysticercosis in humans only develops by this aberrant mechanism.

Clinical features. The clinical presentation is highly variable and can mimic virtually any disease of the CNS, depending upon the number, size, and location of the cysts. In endemic regions neurocysticercosis is a common cause of seizures and should be included in the differential diagnosis of epilepsy. Subarachnoid lesions may cause meningitis, while intraventricular or aqueductal lesions may lead to hydrocephalus. Signs of increased intracranial pressure such as headache, vomiting, and confusion, may be present. An increased risk for cerebrovascular accidents has been reported.

The presenting CNS symptoms are highly dependent upon the host immune response. Enlarging cysticerci may exert a mass effect but as long as the larvae are viable there is relative immune tolerance and minimal inflammatory response. Many patients with viable cysticerci are therefore asymptomatic. Antigen exposure, however, occurs when the larvae degenerate. This leads to an acute inflammatory response with numerous eosinophils and edema. The inflammation subsequently becomes granulomatous and finally forms a fibrous scar. The cysticerci undergo progressive involution during this process. By the stage of fibrous scarring, only fragmented hooklets may be seen, or no identifiable structures may be present within the cystic scar.

Diagnosis and management. CT scan is the most useful initial study and usually diagnostic, particularly if the patient is coming from an endemic area. CSF analysis shows lymphocytic pleocytosis and increased protein with eosinophilia in 50% of cases.

Seizures must be managed with antiepileptic pharmacotherapy. Since most forms of the disease are self limiting, drug therapy is controversial. Treatment with praziquantel for 15-30 days may be used in combination with steroids to suppress CNS inflammation. Albendazole has also been used, but steroids may decrease the effectiveness of the drug. Surgical intervention may be elected for intractable cases.
 
 

Fig. 1. Life cycle of Taenia solium

References:

1. Shandera, W.X., et al. Neurocysticercosis in Houston, TX: A report of 112 cases. Medicine, 73:37-52, 1994.

2. Center for disease control and prevention, Neurocysticercosis update: international task force for disease eradication. MMWR 41:697-698, 1992.