Taenia saginata. Taenia solium

Taenia saginata. Taenia solium

The beef and the pork tapeworms, how to tell their scolices and their proglottids apart, how cattle and pigs carry their cysticerci, and why only the pork tapeworm is dangerous, its eggs growing into cysticerci in people too, in the brain the commonest preventable cause of epilepsy in the world.

Taenia solium and Taenia saginata
On the far left, a short length of an adult Taenia: a small scolex at the top, a thin neck, then a ribbon of proglottids, broader than long near the neck, square in the middle and longer than wide toward the end. Across the top, the two scoleces drawn large, each a rounded, four-sided knob on a short neck with the first young proglottids behind it. Taenia solium's has four suckers, two facing us and two at the sides, and at its apex a small rostellum ringed by a crown of hooks in two rows, large and small. Taenia saginata's has the four suckers but no rostellum and no hooks. Below each, its gravid proglottid drawn large, longer than wide, with the genital pore on one side margin: in T. solium the pink uterus is a stem down the middle with a few thick side branches on each side; in T. saginata many more fine side branches, each forking, all strung with amber eggs. On the right, the egg the two share: round, with a thick, radially striped amber wall round the oncosphere and its six hooks; and below it the cysticercus, a pale bladder with the scolex turned in from one side, its suckers and hooks inside.

Point at a name or a part to light it.

The two tapeworms are told apart by the scolex, armed with hooks in Taenia solium and unarmed in T. saginata, and by the gravid proglottid: 7 to 13 side branches of the uterus on each side in T. solium, 12 to 30 in T. saginata. Their eggs, 30 to 35 µm across, look alike. T. solium's cysticercus can also grow in people, as cysticercosis.

Simplified: not to scale: the adult, metres long, is drawn as a short length beside the enlarged scoleces, proglottids, egg and cysticercus, each at its own size; only the half of the crown of hooks that faces us is drawn, and the adult's small scolex is drawn without its hooks; the gravid proglottids show only the uterus and the genital pore; their remaining ducts, the excretory canals and the nerves are left out, and the side branches are drawn evenly spaced; the cysticercus's scolex is drawn as a knob reaching into the bladder; in life it lies folded inside a spiral canal.

5 sources
  1. Centers for Disease Control and Prevention. DPDx: Taeniasis. Last reviewed 7 June 2024.
  2. Centers for Disease Control and Prevention. DPDx: Cysticercosis. Last reviewed 12 July 2019.
  3. Wikipedia. Taenia solium.
  4. Wikipedia. Taenia saginata.
  5. Marie C, Petri WA Jr. Taenia saginata (beef tapeworm) infection. MSD Manual Professional Edition, 2025.

At a glance

  1. Taenia saginata, the beef tapeworm, and T. solium, the pork tapeworm, live in the small intestine of people, their only definitive host. People are infected by eating cysticerci in raw or undercooked beef or pork.
  2. T. solium's scolex is armed, with a rostellum and two rows of hooks; T. saginata's has only four suckers. Gravid proglottids have 7 to 13 uterine branches a side in T. solium and 12 to 30 in T. saginata.
  3. The adult worms cause few symptoms: abdominal discomfort, and proglottids in the stool or crawling from the anus. A single dose of praziquantel or niclosamide cures them.
  4. T. solium's eggs can also grow into cysticerci in people who swallow them: cysticercosis. It comes from a tapeworm carrier's stool, not from eating pork.
  5. In the brain, neurocysticercosis causes seizures, headache and hydrocephalus, and about 30% of epilepsy where the parasite is common. Its treatment starts with steroids and antiseizure drugs, and anthelmintics only once inflammation and pressure are controlled.

Two tapeworms of people

Taenia saginata and Taenia solium are cyclophyllid tapeworms, named after the animal that carries their larvae: the beef tapeworm and the pork tapeworm. People are the only definitive host of both, and are infected by eating the larvae, cysticerci, in raw or undercooked meat. A third species, T. asiatica, close to T. saginata, is caught in Asia from undercooked pig liver.

Usually only one or two worms live in the gut, attached to the wall of the small intestine by their scolex, and they can live there for years.

The adults

T. saginata, beef tapewormT. solium, pork tapeworm
Lengthusually several metres, up to 25 m2 to 7 m
Proglottids1,000 to 2,000about 1,000
Scolexfour suckers, no rostellum and no hooks: unarmedfour suckers and a rostellum with two rows of hooks, large and small, about 13 of each: armed
Gravid proglottid12 to 30 main uterine branches on each side7 to 13 main uterine branches on each side
Eggs per gravid proglottidup to 100,000up to 50,000
How the proglottids leavethey move: they can crawl out of the anuspassed passively in the stool
Intermediate hostcattlepigs, and people
Cysticercosis in peoplenoyes

T. solium's scolex is about 1 mm across. Behind the scolex, the short neck makes the proglottids, which mature as they move back: the mature ones each hold a full set of male and female organs, opening at a genital pore on one side margin; the gravid ones, longer than wide, are a uterus of branches packed with eggs. The figure shows both scolices and both gravid proglottids side by side.

The egg and the cysticercus

  • The egg is round, 30 to 35 µm, with a thick, radially striated wall round an oncosphere with six hooks. The eggs of T. saginata, T. solium and Echinococcus look the same, so eggs in the stool name the genus but not the species. They are infective as soon as they are passed, and can survive for days to months outside.
  • The cysticercus, or bladder worm, is a fluid-filled bladder, usually 5 to 15 mm long, holding a single scolex turned in on itself. Eaten, the scolex turns out and attaches to the gut wall.

The life cycle

Taenia saginata and Taenia solium: the life cycles
A map of the life cycles of the beef and pork tapeworms. Across the top, the patient's pale panel, the only definitive host: the adult tapeworm lives in the small intestine, grown from a cysticercus in about 2 months. Down the middle, on the white page, eggs and whole gravid proglottids are passed in the faeces, infective at once. Along the foot, three panels. On the left, cattle eat the eggs with soiled fodder, and T. saginata's cysticerci form in their muscle. On the right, a pig does the same with T. solium's. From each, an arrow climbs an outer edge back to the patient, who eats the beef or pork raw or undercooked. In the middle, a person who swallows T. solium's eggs in soiled food or water becomes its accidental intermediate host: cysticerci form in the brain, muscle and skin over 60 to 70 days, cysticercosis, and no arrow leaves this panel.

Point at a name to light its pathway.

People are the only definitive host of both tapeworms: they carry the adult after eating raw or undercooked beef (T. saginata) or pork (T. solium). T. solium is the dangerous one: a person who swallows its eggs, from someone else's faeces or their own, becomes its intermediate host, and its cysticerci can lodge in the brain.

Simplified: a map, not anatomy: the hosts drawn as icons and the parasites drawn small, nothing to scale; the two tapeworms drawn as one cycle: T. saginata goes only through cattle, T. solium through pigs and, by accident, people; one adult and one egg drawn for both; each larva's way from the gut it hatches in to the muscle it settles in, through the blood, drawn as one arrow.

2 sources
  1. Centers for Disease Control and Prevention. DPDx: Taeniasis. Last reviewed 7 June 2024.
  2. Centers for Disease Control and Prevention. DPDx: Cysticercosis. Last reviewed 12 July 2019.
  1. Out in the stool. Gravid proglottids or eggs leave in the stool, about six proglottids a day.
  2. The intermediate host. Cattle (T. saginata) or pigs (T. solium) eat grass or fodder soiled with the eggs or proglottids. The oncospheres hatch in the gut, cross its wall and are carried to the striated muscles, where each becomes a cysticercus, which can live for years.
  3. Back to a person. Someone eats raw or undercooked beef or pork with cysticerci. In the small intestine the cysticercus grows into an adult tapeworm in about 2 months.

People can also be an intermediate host of T. solium. Its eggs, swallowed from a carrier's stool, hatch in the gut just as they do in a pig, and the oncospheres travel in the blood to the tissues, where they grow into cysticerci over 60 to 70 days. This is cysticercosis, and it can happen to anyone near a carrier, even someone who never eats pork. A carrier can also infect themselves, with their own eggs on their hands. T. saginata's eggs do not grow into cysticerci in people.

Taeniasis

Taeniasis, infection with the adult worm, is found wherever undercooked beef or pork is eaten, and most of all where people live close to pigs and cattle without good sanitation.

  • Symptoms: often none. There may be mild abdominal pain, nausea, diarrhoea, epigastric discomfort or hunger pains. Passing a moving proglottid, in the stool or in the underwear, is often what brings the patient, upset, to a doctor. Migrating T. saginata proglottids occasionally cause appendicitis or cholangitis.
  • Diagnosis: eggs or proglottids in the stool; eggs may also be found on an anal swab. Because the eggs are the same, the species is named by a proglottid's uterine branches or by the scolex.
  • Treatment: a single dose of praziquantel, 10 mg/kg, or niclosamide, 2 g in adults. The stool is checked again at 1 and 3 months. Treat a carrier of T. solium with care: if there are unrecognised cysts in the brain, killing them can set off seizures.

Cysticercosis

Cysticercosis is infection of a person's tissues with the cysticerci of T. solium. They form in the muscles, under the skin, in the eyes and in the brain. In most tissues a living cyst stirs little reaction; the trouble starts when it dies, often years later, and releases antigens that inflame the tissue round it.

  • Under the skin and in muscle: small nodules that can be felt and usually cause no symptoms. Cysts in muscle tend to calcify and show on an X-ray.
  • In the eye: loss of sight.
  • In the brain and spinal cord: neurocysticercosis, the most important form.

Neurocysticercosis

Neurocysticercosis is the commonest preventable cause of epilepsy in the world. Where T. solium is common, in Latin America, Africa and Asia, it causes about 30% of epilepsy, and in some communities up to 70%. Its signs depend on how many cysts there are, where, and in what stage:

  • Seizures, among the commonest signs, often years after infection.
  • Chronic headache, and signs of raised intracranial pressure.
  • Hydrocephalus, when cysts in the ventricles or the subarachnoid space block the flow of cerebrospinal fluid.
  • Focal neurological signs, confusion, personality change, or aseptic meningitis. Death can come suddenly.

Cysts in the brain tissue itself are parenchymal; those in the ventricles, the subarachnoid space, the spine or the eyes are extraparenchymal, and are harder to treat. A rare racemose form, in the subarachnoid space, is a cluster of large cysts, usually without a scolex.

Diagnosis

  • Brain imaging, MRI and a non-contrast CT: living cysts, solid nodules, ring-enhancing lesions, calcified cysts, or hydrocephalus.
  • Serology: the immunoblot for T. solium antibodies, on serum or cerebrospinal fluid, confirms it. It cannot tell active from inactive infection, and is less sensitive when there is only one cyst.
  • Stool: most people with neurocysticercosis have no tapeworm, and eggs are found in only about 10 to 30% of them. A negative stool does not rule it out.
  • Finding the cyst in a biopsy, such as of a nodule under the skin, makes the diagnosis certain.

Treatment

Treatment depends on the number, place and stage of the cysts, and is best planned with an expert. In order:

  1. Control the inflammation and the pressure. Corticosteroids (prednisone or dexamethasone) reduce the inflammation round dying cysts; antiseizure drugs treat or prevent seizures; hydrocephalus or cysts in the ventricles may need surgery, a cyst removed through an endoscope or a shunt.
  2. Then kill the cysts, if it will help. Albendazole is the drug of choice; praziquantel is added when there are more than two living (viable) cysts in the brain tissue. The steroids start a few days before and continue during the course.

Prevention

  • Cook beef and pork to at least 63 °C in the thickest part, then let the meat rest for 3 minutes; minced meat to 71 °C. Meat inspection at slaughter finds infected carcasses.
  • Find and treat carriers of T. solium, the source of every case of cysticercosis, and wash hands, above all food handlers.
  • Sanitation, so that no one defecates in the open, and pigs kept away from human faeces.
  • In pigs: the TSOL18 vaccine, which prevents infection, and oxfendazole, which cures pigs already infected; with praziquantel for people, this has cut infection in pigs and people.

Check yourselfAnswer, then say how sure you were: a lucky guess still counts as a weak point.

1How do you tell the scolex of Taenia solium from that of T. saginata?

2A gravid proglottid has 9 main uterine branches on each side. Which species is it?

3How does a person get cysticercosis?

4Why is Taenia saginata much less dangerous than T. solium?

5A patient has neurocysticercosis with raised intracranial pressure. What must not be given first?