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Cysticercosis, or neurocysticercosis, is the most common parasitic infection of the central nervous system worldwide. It is caused by larvae of the tapeworm, Taenia solium, normally found in pork. The larvae, called cysticerci (singular cysticercus; also called bladder worms) form cysts in the body. If these worms are found in the intestine, they cause a different disease that is called teniasis, which is discussed in the Taenia solium and Taenia saginata articles.
Cysticercosis occurs when Taenia solium eggs enter the stomach. This can be from food or water contaminated with infected human fecal material. Also, people with adult tapeworms in their small intestine (teniasis) can autoinfect themselves with cysticercosis by vomiting, which pushes eggs into the stomach. When the eggs return to the intestines, the worms hatch and migrate into the skeletal muscles, heart, eyes and even the brain and spinal cord. Once there, they form small encapsulated cysts containing the worm.
Symptoms
In muscles, cysts cause painless swelling or create nodules under the skin. If cysts form in the eye, they can impair vision by floating in the eye and can cause blindness by causing swelling and detachment of the retina. Heart lesions can lead to abnormal rhythms or heart failure (rare). The most dangerous symptoms are a result of encystment in the central nervous system.
According to a Centers for Disease Control and Prevention Division of Parasitic Diseases, in neurocysticercosis (cysticercosis of the brain), "seizures, and headaches are the most common symptoms. However, confusion, lack of attention to people and surroundings, difficulty with balance, swelling of the brain (called hydrocephalus) may also occur. Death can occur suddenly with heavy infections." Often, there are few symptoms until the parasite dies. When the parasite dies, the host's immune system detects the worm's remains and attacks them, causing swelling and scarring. This is what causes most of the symptoms. Spinal cord lesions can lead to partial loss of motor control, weakness, and even paralysis.
Diagnosis
Neurocysticercosis is difficult to diagnose in its early stage and may be apparent only when the first neurological symptoms start, or when a CT scan, or a MRI of the brain is performed for other reasons. Antibody tests or a biopsy of the affected area may be necessary to complete the diagnosis.
Treatment
The current recommended anti-parasitic drugs for acute cysticercosis are Praziquantel and Albendazole, often in conjunction with steroid anti-inflammatory medication to reduce the swelling (brain edema) that results from immune system attacks on dead worms. If the cyst is in certain locations, such as the eye or the brain, steroids may be started a few days before the antiparasitic, in order to avoid problems caused by swelling. If swelling and immune response are not controlled, the treatment itself can be lethal, so the medication is given in low dosages over several days. Sometimes surgery may be needed to remove the infected area or cysts, but this may be impossible when they are located in areas of difficult or dangerous surgical access. Also, some medications may treat symptoms, such as seizures or irregular heartbeat without affecting the worms.
If the cysticerci has calcified in the brain, or if there is only one lesion, treatment is not considered beneficial.
Prevention
It is possible to avoid infection with T. solium by avoiding undercooked pork and food and water contaminated with human feces. Extra care should be taken in places with poor hygiene or meat inspection laws. Freezing infested pork for a prolonged period will also kill cysticerci.
If a person is already infected with T. solium, they can avoid cysticercosis by treating the infection in the small intestine early, by not ingesting their own feces, and by not vomiting, as this brings eggs to the stomach so they form cysticerci in the small intestine.
References in Popular Culture
House
In the series' pilot episode, the case is solved when the patient turns out to have Cysticercosis.
Notes
- Centers for Disease Control and Prevention Division of Parasitic Diseases fact sheet
"Cysticercosis"