Cysticercosis: How a parasitic infection causes seizures

Epilepsy is more common in developing regions, including Latin America, India, Africa, and China, than developed ones. A parasitic brain disease called cysticercosis is thought to account for almost all of the “extra” epilepsy in these regions. At the 10^th International Child Neurology Congress, held in June 2006 in Montreal, Wendy Mitchell of Children’s Hospital Los Angeles and the Keck School of Medicine, University of Southern California, reviewed the impact of this disease.

What causes cysticercosis?

The pork tapeworm, Taenia solium, is endemic where sanitation is poor and pigs are allowed to roam freely. When a pig consumes tapeworm eggs or segments in human feces, it becomes infected. The eggs hatch in the pig’s digestive tract. Tapeworm larvae migrate to the pig’s muscles and form cysts. If a human eats one of these cysts in undercooked pork, a tapeworm grows in that person’s intestine, completing the life cycle. This type of tapeworm infection is called taeniasis.

Cysticercosis can happen when tapeworm eggs or segments are eaten by humans because of poor sanitation and lack of handwashing. As in the pig, the eggs hatch in the human’s digestive tract. The larvae migrate to the muscles or other tissues, where they form cysts. When a cyst forms in the brain, this is known as neurocysticercosis.

Each cyst contains a living tapeworm larva. A cyst can lie dormant without symptoms for many years. However, when the larva dies, the cyst becomes inflamed. This often causes acute symptomatic seizures.

The acute seizures may go away again in three to six months, after the inflammation dies down. Approximately 30% of people who have such seizures go on to develop chronic epilepsy.

In some cases, depending where they are located in the brain, live cysts may also cause seizures or hydrocephalus. If a person has multiple cysts, these may cause symptoms due to a so-called mass effect.

There have been cases of sudden death due to cysticercosis, often as a result of hydrocephalus.

How common is cysticercosis?

Cysticercosis is usually overlooked until it starts to cause symptoms, and even then it may not be detected without a CT scan. Prevalence studies use blood tests and sometimes CT scans to look for infection, but these methods may not detect all cases. For these reasons, it is hard to tell exactly how common cysticercosis is. However, researchers estimate that in some developing areas, over 10% of people have cysticercosis. In the same areas, it may cause as many as half the cases of epilepsy that start in adulthood.

Cysticercosis also appears to be on the rise in the developed world. In one U.S. study of emergency room patients aged five years or older, 2.1% of patients with seizures had neurocysticercosis. In areas with large immigrant populations, this number rose to almost 10%. So far, most cases of cysticercosis in the United States have been found in recent immigrants, their families, or people who employed them as domestic workers. However, some U.S. studies have found that 17% to 26% of children with the disease were infected in the United States.

Preventing and treating cysticercosis

Handwashing

Once an infection is found, it can be treated with antiparasitic drugs. There is some evidence that de-worming treatment and steroids reduce the risk of later seizures. However, Dr. Mitchell observed that prevention is probably much more effective and less expensive than treatment. The cycle of tapeworm infection is almost completely preventable through:

• improved sanitation, such as plumbing, sanitary latrines, or outhouses
• keeping pigs in fenced areas
• meat inspection
• cutting cysts out of infected pork during butchering
• thorough cooking to kill cysts
• proper handwashing, especially before handling food