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Infectious Disease and Microbiology – Cysticercosis
Cysticercosis is a parasitic infection caused by the larval stage of the pork tapeworm, Taenia solium. Humans develop cysticercosis when they ingest tapeworm eggs, which hatch into larvae (oncospheres) that penetrate the intestinal wall and disseminate hematogenously to tissues. The larvae develop into cysticerci—fluid-filled cysts—within various organs. The central nervous system (CNS) is most commonly affected, a condition known as neurocysticercosis. Other commonly involved sites include skeletal muscle, subcutaneous tissue, heart, and eyes. Many infections remain asymptomatic, but symptomatic disease can result in significant neurologic morbidity.
Cysticercosis occurs worldwide and affects more than 50 million people. It is highly prevalent in Central and South America, sub-Saharan Africa, India, Southeast Asia, and parts of Eastern Europe. In endemic villages, 10% or more of the population may be seropositive, and up to 6% may harbor adult intestinal tapeworms at any time. Neurocysticercosis is the most common parasitic infection of the CNS and is the leading cause of seizures in many developing countries. In Mexico, for example, up to 10% of brain CT scans in some institutions show evidence of neurocysticercosis.
Risk factors include consumption of raw or undercooked pork, poor sanitation, close proximity to pigs (particularly where pigs have access to human feces), and inadequate hand hygiene leading to fecal–oral transmission. Humans are the definitive host for the adult intestinal worm, which resides in the small intestine and sheds eggs or gravid proglottids in stool. Pigs serve as intermediate hosts when they ingest eggs, allowing larvae to encyst in muscle tissue. Humans acquire intestinal tapeworm infection by eating undercooked pork containing cysticerci. In contrast, cysticercosis occurs when humans ingest eggs directly—either through contaminated food or water, poor hygiene, or autoinfection in individuals already infected with the adult worm.
In neurocysticercosis, neurologic symptoms primarily result from the inflammatory response that occurs when cysticerci degenerate. Mass effect may also occur when cysts obstruct cerebrospinal fluid flow, leading to hydrocephalus and increased intracranial pressure. Extraneural disease may involve the eyes (commonly vitreous humor or subretinal space), causing visual disturbance or chronic uveitis. Subcutaneous cysts present as firm nodules that may become inflamed. Skeletal muscle involvement is usually asymptomatic but may produce muscular pseudohypertrophy in heavy infestations. Cardiac involvement can lead to conduction abnormalities.
Clinical manifestations vary widely. Patients may present with chronic headache, seizures, focal neurologic deficits, altered mental status, nausea, vomiting, visual disturbances, insomnia, anorexia, or weight loss. Seizures are the most common presentation. Physical examination often reveals absence of fever, nonfocal neurologic findings, papilledema, hyperreflexia, or visual deficits. Intraocular larvae may be visualized on ophthalmoscopy. Subcutaneous nodules resembling sebaceous cysts may be palpable.
Diagnosis relies on imaging and serologic testing. Brain CT and MRI are key diagnostic tools; MRI is especially useful for detecting brainstem or ventricular cysts. Imaging may show viable cysts, ring-enhancing lesions, or calcified granulomas. Soft tissue radiographs may reveal calcified cysts in muscle. Serologic testing includes enzyme-linked immunoelectrotransfer blot (EITB), which has high sensitivity and specificity in patients with multiple cysts, though sensitivity is lower with single lesions. Stool examination may identify ova and parasites if intestinal infection is present. Lumbar puncture findings are nonspecific but may show lymphocytosis, elevated protein, and decreased glucose in cases with significant inflammation. Biopsy of subcutaneous nodules can confirm the diagnosis.
The differential diagnosis of neurocysticercosis includes brain abscess, neoplasms, tuberculosis, toxoplasmosis, encephalitis, stroke, intracranial hemorrhage, meningitis, and other causes of seizures or focal neurologic deficits.
Treatment includes antiparasitic therapy combined with anti-inflammatory management. First-line therapy consists of praziquantel for two weeks along with corticosteroids (prednisone or dexamethasone) to control inflammation. Albendazole is an effective alternative and is commonly used. Anticonvulsant therapy (e.g., phenytoin, phenobarbital, or benzodiazepines for acute seizures) is required for seizure control. Neurosurgical interventions, such as ventricular shunting or burr hole procedures, may be necessary for obstructive hydrocephalus or elevated intracranial pressure. Ophthalmologic or neurosurgical referral is indicated for ocular or severe CNS involvement.
Prognosis is generally excellent with appropriate diagnosis and treatment, although some patients require long-term anticonvulsant therapy due to persistent calcified lesions. Complications include status epilepticus, stroke, intracranial herniation, hydrocephalus requiring shunt placement, shunt-related complications, and permanent vision loss.
Prevention focuses on improved sanitation, hand hygiene, proper cooking of pork, freezing pork to kill cysticerci, strict meat inspection, treatment of infected individuals, and control of infection in pig populations. Education regarding seizure management and avoidance of high-risk activities after seizures is essential for affected patients.
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