Pigs eat the eggs of these tapeworms when they eat food contaminated with feces. The eggs hatch in the pig intestines and develop into cysticerci in the muscles. Cysticerci are the larval form of the tapeworm.When people eat undercooked meat that is contaminated by cystocerci, they develop into adult tapeworms in the small intestines of humans and release thousands of eggs. Cysterici can also travel to the brain and form cysts when this happens it is known as neurocysticercosis. To appreciate what this looks like, first, here is a picture of a normal slice through the middle of the brain:
Here is a picture of a similar area of the brain contaminated with the pork tapeworm showing cysts:
On the left is a normal picture of the brain on a brain MRI (magnetic resonance imaging) scan. On the right is a brain MRI showing neurocysticercosis:
The appearance of neurocysticercosis in the brain depends on which of the four stages the person is in. In stage 1 (vesicular stage), the worm is alive and there is not a significant response from the immune system so there is minimal edema (fluid build up). In stage 2 (colloidal stage), the worm dies, causing the cyst to weaken, the worm to leak out, and the immune system responds, causing significant inflammation. In stage 3 (granular nodular stage), the immune response causes the cysts to harden and collapse. In stage 4 (calcified stage), the cysts calcify and the immune response/inflammation decreases. At any point, abnormal areas in different parts of the brain can be all in one stage or at either of the 4 stages.
Neurocysticercosis is the most common parasite disease of the nervous system and the main cause of acquired epilepsy (repeated seizures) for people in developing countries. This is because of poor hygiene in many developing countries, especially where pigs and humans live close together. The condition rarely happens in Muslim countries, where eating pork is forbidden. In addition to seizures, other signs and symptoms include headaches, dizziness, stroke (rupture or blockage of a blood vessel in the brain), increased blood pressure in the brain, severe impairment of thinking skills, double vision, difficulty speaking, weakness and/or sensory loss on one side of the body, increased or decreased reflexes, difficulty walking, movement disorders, and increased fluid in the brain.
Neurocysticercosis is treated by administering medications to kill the tapeworms, although these medications are often not used in patients with severe edema because the medication causes additional inflammation. Corticosteroids are administered to reduce inflammation. If seizures occur, anticonvulsants will be used to treat them. In some cases, neurosurgery is performed to remove accessible cysts.
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