Neurocysticercosis is a dangerous disease caused by tapeworm larvae invading the brain and central nervous system. It is usually detected during hospital visits for headaches or seizures and can be prevented by practicing proper hygiene and cooking meats thoroughly. Treatment is controversial and depends on the number, condition, and location of the cysts.
Neurocysticercosis is a disease in which larvae of tapeworms of the genus Taenia invade tissues of the brain and central nervous system to form cysts. These cysts, when present in non-neural tissue, are known as cysticerci. They can form in many soft tissues of the body, including the skin, muscles and heart, but neurocysticercosis is the most dangerous form of infection.
The encysted larvae can exist in a dormant state in the brain for years without provoking an attack by the immune system. It is only when there are large numbers of cysts, or when a cyst dies and releases its contents, that the body mounts an immune response against the invading pathogen. Neurocysticercosis was primarily a disease of the developing world but is becoming more frequently observed in the United States. It is usually detected by magnetic resonance imaging (MRI) during hospital visits for headaches or seizures.
Humans come into contact with tapeworm eggs by ingesting food contaminated with human feces, which contains the eggs. Since the adult form of Taenia solium, the pork tapeworm, can only exist in humans, only human fecal material will contain the eggs. Taenia sanginata, the beef tapeworm, rarely causes neurocysticercosis. The protective covering of the eggs is broken down by the stomach acid and the invasive larvae enter the bloodstream. From there, they can travel to a number of tissues.
Cysticercosis can also form in pigs when they ingest food contaminated with tapeworm eggs. These will hatch and form cysts in the pig’s body. If due care is not taken when processing or cooking pork products for human consumption, the larvae can enter the small intestine through the normal digestive process, latch onto the intestinal wall, and develop into an adult tapeworm. In people who carry an adult tapeworm, self-infection is possible through retroperistalsis, when the contents of the digestive tract move in the opposite direction. This usually occurs during vomiting when adult tapeworm segments containing eggs are pushed back into the stomach and the eggs hatch via the normal route of infection.
Neurocysticercosis can be treated in a variety of ways, depending on the number, condition, and location of the cysts in the nervous system. A single cyst in the eye may require surgical treatment to prevent blindness caused by the cyst pressing against the optic nerve; a cyst in the spine can lead to paralysis; cysticerci in the brain can lead to seizures, depending on their location. A viable larval cyst will elicit only a very weak immune response, but a deteriorating cyst will release its contents into the host environment, which will cause an attack by the immune system.
Whether or not a patient should be treated is a controversial topic. Some researchers believe that the use of antiparasitic drugs that kill the larvae will only aggravate the patient’s symptoms, as it is the dead cyst that causes an immune response. When treatment is prescribed, it usually involves a combination of antiparasitic and anti-inflammatory medications. In many cases, patients with a small number of cysts will not be treated with medications. Surgical removal of cysts is accompanied by anti-inflammatory drugs. Patients whose seizures are caused by a dead cyst usually aren’t treated, but symptoms should lessen as the larvae are gradually cleared from the body over time.
Neurocysticercosis is present in 70% to 90% of patients presenting with acute symptomatic seizures. Seizures usually begin when the cyst is still viable or just starting to escalate. However, chronic seizures are mostly caused by dead cysts. The first epileptic episode usually occurs when the cyst begins to break down, releasing its contents into the brain. The location of the cyst in the brain and the patient’s immune response are the factors that trigger the first crisis. Neurocysticercosis can be prevented by practicing proper hygiene and cooking or freezing meats thoroughly. Be careful with any food from places where human waste can be used as fertilizer.
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