Cysticercosis

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 oncospheres, form cysts in the body. If these worms are found in the intestine, they cause a different disease that is called taeniasis, 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 (taeniasis) 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.

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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, hydrocephalus (compression of the brain tissue due to obstruction of cerebrospinal fluid flow) may also occur." Often, there are few symptoms until the parasite dies.^[1] 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.

When death occurs, it is most often due to involvement of the brain resulting in hydrocephalus, cerebral edema, cerebral compression, or epileptic seizures.^[2]

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 an 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 anti-parasitic drugs Praziquantel and Albendazole may be used to treat neurocysticercosis. Steroid anti-inflammatory medication is also often used in conjunction to reduce the swelling (brain edema) that results from immune system attacks on dead worms. It is still controversial whether patients benefit from treatment, because live cysticerci do not provoke seizures; only dead or dying parasites invoke an inflammatory response and seizures. In theory, therefore, treating a patient with drugs that kill living parasites can induce seizures in someone who is otherwise well and seizure-free; likewise, treating someone with seizures may not have any effect on outcome as the parasites are already dead and no improvement can be expected. A meta-analysis of 11 trials suggest that is that there is probably some small benefit to patients who have active lesions, but no benefit to those with only dead or inactive lesions.^[3]

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.^[1]

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.

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References

1. ^ ^{a b} Centers for Disease Control and Prevention Division of Parasitic Diseases fact sheet
2. ^ Sorvillo FJ, DeGiorgio C, Waterman SH (2007). "Deaths from cysticercosis, United States". Emerg Infect Dis 13 (2): 230–5.
3. ^ Del Brutto OH, Roos KL, Coffey CS, Garcia HH (2006). "Meta-analysis: Cysticidal drugs for neurocysticercosis: albendazole and praziquantel". Ann Intern Med 145 (1): 43–51. PMID 16818928.