What is neurocysticercosis?

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Neurocysticercosis is the most common parasitic infection of the central nervous system (CNS).

The disease affects people who ingest the tapeworm Taenia solium, and it develops when the worm’s larvae build up in the muscles, eyes, skin, and CNS.

The World Health Organization (WHO) report that T. solium may enter the body if a person:

• eats undercooked pork from a pig with the infection
• consumes water that contains the parasite
• has poor hygiene

Reports show that neurocysticercosis affects around 50 million people worldwide, and according to a 2017 entry in the International Encyclopedia of Public Health, the disease is a major cause of epilepsy and seizures across the globe.

There are five stages of neurocysticercosis, and these align with the lifecycle of the parasite that causes it.

Noncystic

At this stage, the embryo of the parasite does not appear on CT or MRI scans.

However, there will be small areas of swelling. Within a few months, these become lesions, as the embryo evolves to form the cysts that characterize this disease.

Vesicular

At this stage, the cysts have translucent walls and hold transparent fluid containing the parasite.

As long as the cysts stay intact, the person tends to have no reaction.

Colloidal vesicular

The cysts develop thick walls, the liquid becomes cloudy, and the person develops an intense inflammatory reaction. This may be due to the parasite beginning to deteriorate, either from treatment or the natural course of the infection.

By this point, a radiographic examination likely reveals cystic lesions with swelling. It is common for the person to experience seizures.

Granular vesicular

At this stage, the swelling has subsided, but seizures can still occur.

Seizures tend to happen during the colloidal and granular stages due to areas of inflammation that surround the dying parasite.

Calcific stage

This occurs after the parasite has died.

According to a 2016 article, the calcifications formed are not solid nodules, but they contain the remnants of the parasitic membranes.

Seizures may still occur due to inflammation related to the exposure of the immune system to remnants of the parasite.

Neurocysticercosis occurs due to infection with the T. solium tapeworm.

A person may develop the infection if they eat pork containing the worm’s larvae. Cooking pork fully kills the parasite, making the pork safe to eat.

A person can also develop the infection if they consume water that contains the parasite.

Other times, poor personal hygiene, particularly among food handlers, can lead to T. solium infection. The WHO emphasize the importance of workplace hygiene and sanitation.

Once a live T. solium tapeworm enters the body, it attaches to the intestinal wall and matures.

The head of the tapeworm contains many small segments called proglottids, each of which contains a complete reproductive system. There are 1,000–2,000 fertile eggs in each of these segments.

The person passes these eggs out in stool. The larvae then live in environments such as soil, water, and vegetation, where they may be ingested by a pig or human.

A pig’s body cannot completely support the parasites, so the larvae do not fully develop. However, the human body contains the necessary enzymes.

If, after ingesting the parasite, the tapeworm stays at the opening of the person’s bowels, it can cause a disease called taeniasis.

However, if a person consumes the parasite’s larvae, they are at risk of cysticercosis. The larvae may enter the body through food contaminated with feces or via hand-fecal-oral transmission.

Also, the parasitic embryos can enter the body’s tissues and develop into larvae, causing cysticercosis.

If the growing parasites attach anywhere in the CNS, neurocysticercosis can develop.

According to a report from 2014, symptoms of neurocysticercosis depend on where the lesions form, the extent of the infection, and the person’s immune response.

Still, many people with neurocysticercosis have no symptoms. Other people may take months or years to start developing symptoms, according to 2017 treatment guidelines.

Cysts, called cysticerci, can develop in the muscles, eyes, brain, and spinal cord. The person’s symptoms can also depend on the location, size, number, and stage of these cysts.

Common symptoms and signs include:

• seizures
• chronic headaches
• increased pressure in the brain

Seizures are the most common symptom and are often the only indication of the disease. Recurring seizures affect 50–70% of people with neurocysticercosis.

Other symptoms can include:

• neurological problems that affect the function of the spinal cord, brain, or nerves
• reduced ability to think and remember

Neurocysticercosis can sometimes cause combinations of neurological issues or syndromes.

Treatments focus on removing the parasite and managing symptoms, by controlling seizures, swelling, and intracranial hypertension, for example.

The right course of treatment will also depend on the position, size, abundance, and maturity of the parasites.

After assessing the person’s symptoms and the extent of the infection, a doctor may use antiparasitic and anti-inflammatory therapy. In some cases, surgery is necessary to remove cysts.

For people with symptoms and multiple noncalcified cysts, doctors can use certain drugs to expel the parasites, which is known as anthelmintic therapy. This approach, however, is not suitable for people with calcified cysts.

A doctor may also administer steroids to suppress the inflammatory response and anticonvulsant therapy to suppress seizures.

In areas where neurocysticercosis is common, vets can treat pigs with vaccines and anti-parasitic medication to stop the cycle of disease.

Recovery time depends on a range of individual factors, but the number of people who fully recover is growing, due to medical advances.

T. solium infections mostly occur in rural farming communities where pigs come into contact with human feces. However, a rise in international travel has led to the spread of the infection to other areas.

People also have a higher risk of contracting cysticercosis or neurocysticercosis if a member of their household has the infection.

Neurocysticercosis can cause severe complications, primarily stroke, as well as death. Research suggests that 4–12% of people with the disease experience a stroke as a result.

Also, if surgery to remove the cysts is necessary, this increases the chance of additional infections.

Diagnosis largely depends on the combination of symptoms.

As neuroimaging technology has advanced, neurocysticercosis diagnoses have become more accurate over recent years.

A doctor may also use an antibody-specific blood test to support the neuroimaging results.

A person should see a doctor if any symptoms of neurocysticercosis develop.

This is particularly likely if:

• a person lives in an area where T. solium infection is common
• a person has recently visited an area where the infection is prevalent
• a family member has or has had the infection

The outlook for neurocysticercosis depends on how many parasites are present and where they reside in the body.

If the tapeworms have formed many lesions or cysts in the brain, for example, neurocysticercosis can be life threatening and cause frequent seizures.

However, a person with a single lesion on the brain has a good chance of survival and is less likely to experience recurrent seizures.

Neurocysticercosis is the most common parasitic disease that affects the CNS.

Depending on the location of the parasites, neurocysticercosis can cause a range of neurological issues, including recurring headaches, excess pressure within the skull, and changes in thinking and behavior.

Neurocysticercosis is relatively rare in the United States, but there have been more cases in recent years, due to international travel.

Anyone who has symptoms should see a doctor, particularly after traveling to an area where the infection is common.