Tapeworm infections: neurocysticercosis and hydatid disease

• Taeniasis is the adult tapeworm of Taenia solium living in the human small bowel. Cysticercosis is the cyst form that the same organism forms in human tissues, and neurocysticercosis is what happens when those cysts reach the brain. Neurocysticercosis is one of the commonest preventable causes of epilepsy worldwide.^[1]
• A tapeworm is caught by eating undercooked pork that contains cysts. Cysticercosis, including brain cysticercosis, is caught by swallowing eggs shed in the stool of a tapeworm carrier. The same species does both, and mixing up the two routes is the characteristic error.^[3]
• Neurocysticercosis is diagnosed by imaging. Magnetic resonance imaging and non-contrast computed tomography together classify the disease, and enzyme-linked immunotransfer blot confirms it.^[3][4]
• Viable brain cysts are treated with albendazole, with or without praziquantel, alongside corticosteroids that are started first, with antiepileptic drugs for seizures.^[4]
• Hydatid disease is a different parasite with a different life cycle: a Echinococcus granulosus cyst growing most often in liver or lung. Management follows the WHO-IWGE ultrasound stage and combines albendazole, PAIR and surgery, with observation for inactive cysts.^[6][7]
• Treating tapeworm carriers is transmission control: a patient with neurocysticercosis needs contact screening and family follow-up.^[4]

By the end of this page you should be able to:

1. Explain the difference between Taenia solium taeniasis, cysticercosis and neurocysticercosis, and how each is acquired.
2. Describe how a cysticercus develops in tissue and why brain infection causes seizures, raised intracranial pressure or hydrocephalus.
3. Choose and interpret imaging for neurocysticercosis and for a hydatid cyst, including the WHO-IWGE ultrasound stage.
4. Treat an identified tapeworm carrier and plan antiparasitic, anti-inflammatory and antiepileptic treatment for neurocysticercosis by lesion type.
5. Manage an Echinococcus granulosus cyst by stage, including when PAIR, surgery or observation is appropriate.
6. Adjust management in pregnancy, children, people with raised intracranial pressure and low-resource settings.

Neurocysticercosis is commonly separated into:

• Viable parenchymal neurocysticercosis: one or more living cysts with a scolex in brain tissue.
• Single enhancing lesions: an inflammatory, degenerating cyst showing as a ring-enhancing nodule on imaging.
• Calcified parenchymal neurocysticercosis: old, dead, mineralised foci that behave as a seizure focus.
• Extraparenchymal neurocysticercosis: cysts in the ventricles or subarachnoid space, often presenting with hydrocephalus or meningitis.

The key distinction to hold on to: only human cysticercosis, not taeniasis, spreads person-to-person through the faecal-oral route. Controlling taeniasis, by identifying and treating carriers, is how you control cysticercosis.^[3]

Taenia solium persists wherever pigs eat faecally contaminated food and humans eat undercooked pork. Cysticercosis is therefore found in parts of Africa, Asia (including India, China and Nepal) and Latin America.^[3] The WHO estimates that 2.56 to 8.30 million people worldwide have symptomatic or asymptomatic neurocysticercosis.^[1][2] It is estimated to account for up to 30% of epilepsy in endemic areas and up to 70% in some high-risk communities.^[1] Neurocysticercosis is among the leading preventable causes of epilepsy worldwide.^[2]

The burden is concentrated where people and free-roaming pigs live close together and sanitation is poor. In 2015 the WHO Foodborne Disease Burden Epidemiology Reference Group identified T. solium as a leading cause of deaths from food-borne disease, with an estimated 2.8 million disability-adjusted life years, largely in low and lower-middle income settings.^[1] More than 80% of the world's 50 million people living with epilepsy are in those settings.^[1]

Cystic echinococcosis follows the geography of sheep and dogs. Echinococcus granulosus (sensu lato) is cosmopolitan but most heavily endemic in western China, central Asia, South America, the Mediterranean basin and eastern Africa.^[5][6] Reported human incidence in endemic areas ranges from less than 1 to 200 per 100,000 for cystic echinococcosis and from 0.03 to 1.2 per 100,000 for alveolar echinococcosis.^[6] The global burden is estimated at about 285,500 disability-adjusted life years for cystic echinococcosis (over 1 million if underreporting is counted) and about 666,434 for alveolar echinococcosis.^[6]

Mortality is comparatively low but morbidity is substantial: untreated cystic echinococcosis carries a mortality of about 2 to 4%, whereas untreated alveolar echinococcosis kills more than 90% of patients within 10 to 15 years.^[6] Almost all primary alveolar lesions are hepatic.

The adult tapeworm lives in the human small intestine for 2 to 3 years and sheds proglottids packed with eggs. Eggs or whole proglottids are passed in faeces. Pigs become infected by eating contaminated feed, and the parasite develops into cysticerci in pig muscle. A human who eats undercooked pork containing viable cysticerci becomes a tapeworm carrier. This is taeniasis: usually few symptoms, sometimes abdominal pain, nausea, a change in bowel habit or, rarely, more noticeable effects.

Human cysticercosis arises by a different route. A person swallows Taenia solium eggs, often by the faecal-oral route, in food or water or from the hands of a carrier. Oncospheres hatch in the intestine, enter the blood stream and lodge in tissues, maturing into cysticerci over 60 to 70 days.^[3] The cysticercus is a thin-walled, fluid-filled sac containing a single invaginated scolex with hooks; cysts are typically 5 to 15 mm long and may reach 5 cm.^[3] Which symptoms appear depends on which tissue is involved. When the central nervous system is involved, the cysts behave in one of three broad ways:

• Viability and inflammation. A living cyst is often well tolerated. Symptoms appear when it begins to degenerate and the host immune response reacts: oedema, seizure focus and enhancement. A degenerating cyst is often the most symptomatic phase of parenchymal disease.
• Mass effect and obstruction. Large cysts or aggregates (including racemose extraparenchymal forms) can displace structures, obstruct cerebrospinal fluid flow and produce hydrocephalus.
• Calcification. A dead cyst may calcify and leave a small irritative focus that can generate seizures long after the parasite is dead.

Taeniasis, by comparison, is usually relatively mild: symptoms are abdominal pain, nausea, diarrhoea or constipation that can continue until the tapeworm dies following treatment.^[1] Untreated T. solium infection generally persists for 2 to 3 years.^[1] Propagation of infection in a community is driven by carriers, which is why household screening matters.

Humans are aberrant intermediate hosts. Eggs shed in dog faeces are swallowed, oncospheres hatch in the intestine and are carried in the portal venous system to the liver (about 70% of human cysts), the lungs (about 20%) and less often the brain, bone, heart, spleen or other organs. Each oncosphere becomes a hydatid cyst with a thick laminated wall, a germinal layer and brood capsules that bud protoscolices inside the fluid. Cysts grow slowly over years and may become very large before causing symptoms. Cyst rupture releases protoscolex-rich fluid, causes a granulomatous reaction and may produce secondary (daughter) cysts elsewhere in the body. It can also provoke an anaphylactic reaction. In regions where both Taenia solium and Echinococcus occur, hydatid disease is a different problem with a different tempo, and the two should not be treated as one. ^[6]

A detailed cyst structure matters surgically. The laminated and germinal layers form the endocyst; surrounding host tissue forms the pericyst. Removing the whole cyst with its pericyst is curative, while opening the cyst risks spilling viable protoscolices.

Most carriers are asymptomatic. When symptoms occur they are mild and non-specific: abdominal pain, nausea, vomiting, diarrhoea or constipation and, in some cases, increased appetite or weight loss. Anal passage of motile proglottids is common and may be the only sign. Pruritus ani and vague upper abdominal discomfort also occur. Taeniasis is easily missed and is usually found through screening.

The hallmark is seizures. The clinical picture depends on the number, size, location and developmental stage of cysts, as well as the host inflammatory response.^[1]

Parenchymal disease

• Viable cysts: seizures are most likely when they begin to degenerate. Headache is common. Some patients are entirely asymptomatic and the cyst is found on imaging done for another reason.
• Single enhancing lesions: a degenerating cyst presents with focal seizures, headache and sometimes transient neurological deficit. The lesion usually resolves over months.
• Calcified parenchymal neurocysticercosis: a remote calcified scar that acts as a seizure focus. It can also produce recurrent perilesional oedema with transient symptoms years later.

Extraparenchymal disease

• Intraventricular cysts: cause hydrocephalus, raised intracranial pressure, vomiting and papilloedema; fourth-ventricular cysts can produce acute obstructive hydrocephalus.
• Subarachnoid (basal cistern or Sylvian fissure) disease: chronic meningitis, hydrocephalus, vasculitis and stroke may occur, and cysts may be racemose.
• Spinal cysts: back pain, radiculopathy or cord compression.
• Ocular cysts: visual impairment, often needing surgical rather than medical management.

Raised intracranial pressure must be excluded before giving antiparasitic therapy, because the inflammatory reaction to dying parasites can worsen cerebral oedema.^[4]

Most hepatic cysts grow slowly and are found incidentally, or cause right upper quadrant discomfort, a palpable hepatomegaly or a cholestatic picture if the cyst communicates with the biliary tree. Lung cysts cause cough, haemoptysis, chest pain and wheeze. Brain cysts are rare and cause focal deficits or raised intracranial pressure. Bone cysts are particularly difficult, because the laminated layer may not form in the same way and recurrence is common. Symptoms may appear after rupture, which can produce anaphylaxis, fever, urticaria or new metastatic cysts.

Hydatid disease of the liver in particular must be distinguished from a simple hepatic cyst, amoebic abscess, pyogenic abscess, cystadenoma, echinococcal pseudocyst and malignancy. Ultrasound, combined with serology and epidemiology, usually points to the diagnosis.

The IDSA recommendations are a good practical standard:

1. Take a careful history and examine the patient, then image the brain.^[4]
2. Use both brain MRI and non-contrast CT for classification of newly diagnosed neurocysticercosis. MRI is better for cystic and intraventricular forms and for oedema; CT shows calcifications best.^[4]
3. Confirm with serology: enzyme-linked immunotransfer blot, on serum and on cerebrospinal fluid when the diagnosis is uncertain. Enzyme-linked immunosorbent assays with crude antigen have poor sensitivity and specificity and should be avoided.^[4]
4. Before starting antiparasitic therapy, check the fundus (ocular cysticercosis changes management), and screen for latent tuberculosis and Strongyloides stercoralis if prolonged corticosteroids are likely.^[4]

Lumbar puncture and cerebrospinal fluid are not routine but are helpful in subarachnoid or ventricular disease. Electroencephalography is used to classify seizures. Not every patient with a calcified focus and a first seizure needs a lumbar puncture.

Diagnosis rests on imaging supported by serology. Ultrasound is the first investigation for liver and abdominal cysts; it stages the cyst at the same time as detecting it. Chest X-ray and CT are used for lung lesions; MRI and CT complement ultrasound when the cyst is inaccessible or complicated. CT and MRI images can be characteristic (heterogeneous mass with calcification and necrotic centre for alveolar disease, clear fluid and laminated wall for cystic disease).^[6]

Serology has limits and these matter in practice: a cyst may be well encapsulated and the host may not make detectable antibodies. Reported sensitivity and specificity of serological methods for confirmed cystic disease range from 60 to 90%, depending on the antigen, cyst stage and location. Newer methods, such as enzyme immunoassay or haemagglutination screening with immunoblot confirmation, are used where available. In seronegative patients with imaging compatible with echinococcosis, ultrasound-guided biopsy with care for spillage and allergic reaction may be needed.^[5][6]

Rather than memorise a staging table, think in terms of stage plus location:

• Viable: cyst with scolex, no perilesional oedema or enhancement. Single (1 or 2) or multiple (more than 2).
• Degenerating or transitional: ring-enhancing cyst with surrounding oedema; single or multiple.
• Calcified: calcified spot, often with a low-echo nodule.

Classification by MRI and CT together determines treatment. The IDSA guidelines treat one to two viable parenchymal cysts differently from more than two.^[4]

The WHO-IWGE ultrasound classification is the basis of hydatid treatment and is worth learning as stages rather than letters:

• Active stages. CE1 (unilocular, anechoic cyst with visible cyst wall or double-line sign) and CE2 (multiseptated or multivesicular "rosette" cyst with daughter cysts). These are biologically viable.
• Transitional stage. CE3, split into CE3a (with detached floating membrane) and CE3b (with daughter cysts not communicating with the main cavity). CE3a is transitional; CE3b behaves more like a viable cyst.
• Inactive (degenerating) stage. CE4 (heterogeneous or hypoechoic content without daughter cysts, no live protoscolices) and CE5 (calcified, often thick wall). CE4 is usually inactive; CE5 clearly so, and both can be observed if stable.
• Alveolar echinococcosis is staged differently, with the PNM classification, but it is enough here to note that P means hepatic localisation, N means neighbouring organs and M means metastases.

Helminth cysts are not "cured" when they shrink on imaging: follow-up must be long enough to declare inactivity.

The person with taeniasis is the source of human cysticercosis. Treatment removes both the carrier state and the egg input:

• Praziquantel 10 mg/kg as a single oral dose.^[1]
• Niclosamide: adults and children over 6 years, 2 g; children aged 2 to 6 years, 1 g.^[1]
• Albendazole 400 mg orally once daily for 3 consecutive days has also been used.^[1]

The supporting therapy is hygiene and sanitation: proper disposal of human faeces, meat inspection and, where available, veterinary intervention such as vaccinating pigs with TSOL18 and treating them with oxfendazole. Preventive chemotherapy at community level is organised under the PAHO/WHO guideline for preventive chemotherapy for the control of T. solium taeniasis.

Care is needed with praziquantel in someone who may also have cysticercosis, because the drug crosses the blood-brain barrier and can provoke inflammation around brain cysts. When a patient has both neurocysticercosis and taeniasis, the neurocysticercosis is treated first, with steroid cover, and taeniasis is cleared later with an appropriate regimen and precautions.

Key management points from current sources:

• Antiparasitic treatment is indicated for every patient with viable parenchymal neurocysticercosis and no raised intracranial pressure, rather than support alone.^[4]
• Adjunctive corticosteroids, begun before antiparasitic drugs, are recommended for all patients treated with antiparasitic therapy, to control the inflammatory reaction to dying parasites.^[4]
• Albendazole is the standard drug: 15 mg/kg/day, split into two daily doses, for 10 to 14 days, taken with food, with a maximum total of 1200 mg/day.^[4]
• For patients with more than 2 viable parenchymal cysts, use albendazole 15 mg/kg/day combined with praziquantel 50 mg/kg/day for 10 to 14 days.^[4]
• Single enhancing lesions are treated with albendazole 15 mg/kg/day in twice-daily doses for 1 to 2 weeks, with meals.^[4]
• Antiparasitic therapy for subarachnoid neurocysticercosis should continue until viable cysticerci resolve on imaging and the other evidence of parasite activity subsides, often requiring more than a year. High-dose corticosteroids are started before antiparasitic therapy, and methotrexate can be considered as a steroid-sparing agent.^[4]
• For intraventricular disease, removal by minimally invasive neuroendoscopy is preferred for lateral and third ventricular cysts, surgery is preferred for fourth ventricular cysts, and shunt surgery plus medical therapy is used when removal is impractical. Corticosteroids reduce brain oedema around procedures. Antiparasitic drugs after shunt insertion, alongside steroids, decrease later shunt failure when removal was not possible, but they are not needed after successful removal.^[4]
• In calcified parenchymal neurocysticercosis, symptomatic treatment rather than antiparasitic drugs is recommended, and corticosteroids are not routinely used in isolated disease with perilesional oedema. Refractory epilepsy may warrant evaluation for surgical removal of the seizure focus.^[4]
• Antiepileptic drugs are recommended for all patients with neurocysticercosis and seizures. If cysts have resolved on imaging and there have been no seizures for 24 consecutive months, tapering and stopping antiepileptic drugs is reasonable for patients with few initial seizures.^[4]
• Follow-up MRI is repeated at least every 6 months until the cystic component resolves for viable parenchymal disease and for single enhancing lesions.^[4]
• Patients treated with albendazole for more than 14 days should have periodic monitoring for hepatotoxicity and leukopenia. Combination albendazole plus praziquantel needs no monitoring beyond that recommended for albendazole alone.^[4]
• Intraocular cysticerci are treated with surgical removal rather than antiparasitic drugs.^[4]

• Raised intracranial pressure. Manage the pressure first with anti-inflammatory and surgical measures. Do not start antiparasitic therapy while untreated hydrocephalus or diffuse oedema is present.^[4]
• Pregnancy. Defer antihelminthic therapy until after delivery; intracranial hypertension must be managed aggressively, corticosteroids can be used when needed, methotrexate must be avoided, and antiepileptic drugs must take teratogenicity into account.^[4]
• Children. Management is the same as adults for the same disease form, with weight-based dosing.^[4]
• Spinal neurocysticercosis. Individualise between medical therapy (antiparasitic plus anti-inflammatory) and surgery, especially in the presence of cord dysfunction.^[4]
• Consultation. Complex extraparenchymal or refractory disease should be discussed with a neurologist or neurosurgeon before definitive treatment.^[4]

A stage-based approach, guided by the WHO-IWGE classification and the expert consensus, is the recommended model of care.^[6][7]

Key hydatid management points:

• Albendazole is the drug of choice for cystic echinococcosis, at an average dosage of 15 mg/kg/day. Mebendazole is reserved for patients who cannot tolerate albendazole.^[6]
• Anti-infective treatment alone is reserved for small or medium-sized isolated cysts, or for multiple and inoperable cysts in liver or several organs.^[6]
• PAIR has become a standard interventional option for medium CE1 and CE3a cysts, performed by experienced operators with concurrent albendazole.^[6]
• The WHO-IWGE recommends 20% hypertonic saline as the preferred protoscolecide in surgery and 20% hypertonic saline or 95% alcohol in PAIR.^[6]
• Complete (total) removal of the cyst, including its pericyst, is the curative surgical goal for cystic echinococcosis. Less than complete removal obliges the use of protoscolecidal agents and antiparasitic cover.^[6]
• Curative surgery in alveolar echinococcosis is combined with 2 years of albendazole at the same dosage and with the same precautions as for cystic disease; when resection is impossible, albendazole is continued continuously.^[6]
• Percutaneous injection of a protoscolecide should never be used in alveolar echinococcosis, because the cavity is necrotic debris rather than accessible cyst fluid and bile ducts are usually involved.^[6]

• Cyst rupture and anaphylaxis in hydatid disease; sudden onset fever, urticaria, eosinophilia and possible shock. Rupture into a bronchus can produce expectoration of "hydatid sand".
• Biliary communication with a hydatid cyst causes cholangitis, jaundice or a biliary fistula. Communication with the biliary tree must be excluded before any protoscolecide is injected.^[6]
• Secondary echinococcosis after spillage of protoscolex-rich fluid.
• Perilesional oedema around calcified neurocysticercosis can produce transient neurological episodes years later; it is not a drug emergency by itself.
• Persistent raised intracranial pressure from hydrocephalus in neurocysticercosis can cause herniation if antiparasitics are given too early.

• Most viable parenchymal neurocysticercosis responds to antiparasitic and anti-inflammatory therapy; follow-up MRI every 6 months is recommended until the cystic component resolves.^[4]
• Calcified lesions may be a lifelong, low-grade seizure trigger.
• Cystic echinococcosis has a recurrence rate, particularly after partial rather than total cystectomy; follow-up should continue for at least 5 years and longer in complicated or alveolar disease. Regular blood counts and liver function tests in the first 6 months of benzimidazole therapy detect the serious, limiting toxicities. Serum cysticercal or echinococcal antigen markers are useful after complete resection for detecting recurrence.^[6]
• Untreated alveolar echinococcosis is a progressive, ultimately fatal disease, with more than 90% mortality within 10 to 15 years in untreated or inadequately treated patients; modern imaging combined with continuous albendazole and curative surgery where possible has greatly improved long-term survival.^[6]

• Taeniasis control: identify and treat carriers (praziquantel 10 mg/kg), improve meat inspection, discourage consumption of raw or undercooked pork, and interrupt the human-pig cycle with pig vaccination and oxfendazole.^[1]
• Cysticercosis control: the same; plus sanitation to prevent pigs and humans from accessing human faeces, health education and, in some settings, mass screening of human stools.
• Hydatid control: deworming dogs with praziquantel 8 times per year in high transmission zones, vaccinating sheep (the EG95 recombinant vaccine), improving slaughterhouse hygiene, safe disposal of offal and public education.^[6]
• Clinical prevention in individuals: travel and food hygiene; consuming only well-cooked pork; washing hands after any contact with dog saliva or faeces in endemic regions.

• Where CT or MRI is unavailable, neurocysticercosis is often treated empirically for epilepsy on the strength of epidemiology and a clinical picture, and imaging, when it finally arrives, usually confirms a compatible picture.
• Non-contrast CT alone will miss viable and intraventricular cysts but will show calcifications; MRI is rarely available in the most affected areas. Ultrasound is the realistic staging tool for hydatid cysts.
• Albendazole is widely available and inexpensive, praziquantel less so. Corticosteroids (prednisolone, dexamethasone) and antiepileptic drugs are the backbone of symptomatic care.
• Surgery for hydatid cysts and neuroendoscopy for neurocysticercosis are concentrated in referral centres; total cystectomy may be impractical and partial cystectomy with protoscolecide may be the local standard.
• In all such settings, primary prevention through sanitation and pig and dog control has more impact than tertiary treatment.

Antihelminthic therapy should be deferred until after delivery in pregnant patients with cysticercosis. Intracranial hypertension must still be treated aggressively, and corticosteroids can be used when needed. Antiepileptic drugs should be chosen with altered pharmacokinetics and teratogenicity in mind (phenobarbital and valproic acid in particular are known teratogens). Methotrexate is teratogenic and must be avoided.^[4]

Children with neurocysticercosis are managed on the same principles as adults, with weight-based dosing. Most hydatid cyst acquisitions are in childhood, but symptoms appear years later. Dosing of all drugs is therefore by body weight.

There is limited specific evidence in this population. Prolonged steroid courses will suppress immunity further and predispose to tuberculosis and Strongyloides infection. Screening for latent tuberculosis and Strongyloides before starting prolonged steroids is therefore appropriate.^[4]

• Neurocysticercosis is Taenia solium in the brain. It is caught by swallowing eggs shed by a tapeworm carrier. Taeniasis itself is caught from undercooked pork. Do not confuse the two routes.
• The clinical phases are viable cyst (often quiet), inflammatory degeneration (symptomatic, seizures), calcified scar (a seizure focus).
• Diagnosis combines brain MRI and non-contrast CT with confirmation by enzyme-linked immunotransfer blot. CT shows calcification best, MRI shows cysts and oedema best.
• Viable parenchymal disease should be treated with antiparasitic therapy unless there is raised intracranial pressure or oedema.
• Adjunctive corticosteroids are started before antiparasitic therapy in every treated patient.
• Antiepileptic drugs are used for all patients with seizures and can be tapered after resolution and 24 months seizure free in patients with few initial seizures.
• Standard albendazole dose is 15 mg/kg/day divided into two daily doses for 10 to 14 days with food, with a maximum of 1200 mg/day. Combination with praziquantel 50 mg/kg/day is used for more than 2 viable cysts. ^[4]
• Single enhancing lesions are treated with albendazole 15 mg/kg/day twice daily for 1 to 2 weeks.
• Calcified disease is managed symptomatically, not with antiparasitics.
• Intraventricular and subarachnoid disease needs prompt specialist, often surgical, management: neuroendoscopy for lateral and third ventricular cysts, surgery for fourth ventricular cysts, shunt plus medical therapy for subarachnoid cysts.
• Hydatid disease is a different illness, staged with the WHO-IWGE ultrasound classification: active (CE1, CE2), transitional (CE3a, CE3b), inactive (CE4, CE5).
• Albendazole at about 15 mg/kg/day is the drug of choice for cystic echinococcosis; mebendazole is the alternative.
• PAIR is for medium CE1 or CE3a cysts; total cystectomy is the curative operation. Hypertonic saline 20% is the preferred intraoperative protoscolecide.
• Stable inactive (CE4 and CE5) cysts are watched, not treated.
• Treatment breaks the local chain only when carriers are found and treated.

• Prerequisites and natural follow-ons: seizures and epilepsy, chronic headaches, hydrocephalus, and epidemiology of cystic echinococcosis in low-resource settings are good next reading.
• Related topics include brain abscess, tuberculous meningitis, headache, epilepsy and cystic echinococcosis work-up.
• Planned topics for cross-linking once published: cysticercosis, epilepsy, headache, neuroinfection, abdominal imaging and travel medicine.