As the film explains, the woman, who lives in Arizona, first started to experience flu-like symptoms, followed by numbness in her left arm which grew progressively worse. Neurosurgeon Peter Nakaji operated, expecting to find a tumour in the brainstem, but instead found and removed a tapeworm.
It goes on to say that the woman was infected either by eating uncooked pork or unwashed food contaminated with infected human faeces (making this most probably a pork tapeworm infection); that this was the sixth such case seen by Nakaji in the past few months; and that this is extremely rare but has started to increase recently.
Horrific as this all sounds, the woman in the film was in fact very fortunate, because if it had been the tapeworm larvae, instead of the worm itself, which had entered her brain, the consequences of her infection would have been much more severe.
The pork tapeworm, Taenia solium, is the most common brain parasite in the world: it has infected more than 50 million people, kills some 50,000 people every year and is the leading cause of epilepsy in parts of the developing world. T. solium is endemic in Latin America, and is therefore becoming a public health problem in the United States, due to immigration. In the southwestern U.S., this parasite accounts for about 10% of patients who visit emergency rooms with seizures.
The most serious consequence of infection is a disease called neurocysticercosis, which occurs when the larval cysts (or cysticerci) of the parasite enter the central nervous system and become lodged in the brain, spinal cord or eyes. When the cysts start to degenerate, they are engulfed by immune cells which try to destroy them, but which then clump together to form structures called granulomas, which harden as a result of calcium deposition. These calcified cysts, or lesions, are the pathological hallmarks of neurocysticercosis. The degenerating cysts can be 4 cm or more in diameter and so cause extensive tissue damage. The symptoms that occur as a result depend on the number and location of cysticerci.
Most often, the cysts lodge in the grey matter, leading to epileptic seizures (see this new study which suggests that seizures are also associated with the fluid-filled cavities that surround the cysts); if attached to the ventricles, they cause headaches, nausea, and dizziness; if in the cerebellum, the symptoms include impaired balance; and in the eye, blurred vision. Hydrocephalus and inflammation of the brain are also common symptoms, and often lead to severe brain damage or even sudden death as a result of cardiovascular problems.
However, T. solium has a complex life cycle which involves the pig as an intermediate host, and whether or not an infection leads to neurocysticercosis depends on when in the parasite’s life cycle the infection occured. Infection normally takes place by ingestion of cysticerci in uncooked meat. The cysts enter the small intestine and attach themselves to the intestinal wall with the scolex (above), an organ consisting of four large suckers and a double row of hooks. This then grows into an adult tapeworm, which can reach to up to 7 meters in length. Under some circumstances, a small adult worm can enter the brain.
An adult worm living in the intestine produces hundreds of thousands of eggs which are removed in the faeces, and so can easily be ingested in unsanitary conditions or because of unhygenic practices, thus completing the parasite’s life cycle. The eggs hatch upon exposure to the stomach acids and begin to grow into larvae called oncospheres which in turn develop to form cysticeri. These then enter the bloodstream and migrate to other parts of the body.