Cysticercosis, or neurocysticercosis, is the most common parasitic infestation of the central nervous system worldwide. Humans develop cysticercosis when they ingest eggs or larvae of the tapeworm Taenia solium. The eggs and larvae are usually found in fecally-contaminated water and undercooked pork.
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.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
Cysticercosis is caused by swallowing eggs from T. solium, which are found in contaminated food. Autoinfection is when a person is already infected with adult T. solium, then swallows eggs following improper hand washing after a bowel movement. Risk factors include eating pork, fruits, and vegetables contaminated with T. solium as a result of unhealthy cooking preparation. The disease can also be spread by contact with infected people or fecal matter. The disease is rare in the United States, but is common in many developing countries.
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.
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 suggests that there is probably some small benefit to patients who have active lesions, but no benefit to those with only dead or inactive lesions.