Taenia sp ------------------------------------------ Taeniasis (Tapeworm)
Of 32 recognized species of Taenia, only Taenia solium and Taenia saginata are medically important. However, recent
epidemiologic studies in Southeast Asia have identified a third Taenia species in humans, known as the Asian species.
Adult tapeworms live in the human small intestine. Humans pass gravid eggs in feces; these mature eggs contaminate
pastures and barnyards, where cattle and pigs ingest them. Upon reaching the alimentary canal of infected animals, the
embryos are released, penetrate the gut wall, and enter the circulation. The embryos filter from the circulation and
encyst in muscular tissue. Larvae (ie, cysticerci) become infectious within 2-3 months. Humans develop a tapeworm
infection by eating raw or undercooked beef or pork. The cysticercus becomes activated, attaches to the wall of the
small intestine by the scolex, and becomes a mature tapeworm. This maturation process takes 10-12 weeks for T
saginata and 5-12 weeks for T solium. A single tapeworm produces an average of 50,000 eggs per day and may live 25
Locally acquired infections have been confirmed in Los Angeles, New York, Chicago, and elsewhere. Although T
saginata infection occurs worldwide, prevalence in the United States is less than 1% because most US cattle are free of
Most intestinal taeniid infections are asymptomatic. When symptoms occur, they usually are mild and involve abdominal
pain, anorexia, weight loss, or malaise. Cysticercosis causes a mass effect in various vital organs (eg, brain, eye, heart).
The mortality rate for cysticercosis is low and is generally caused by complications such as encephalitis, increased
intracranial pressure secondary to edema and/or hydrocephalus, and stroke.
Abdominal pain and nausea are reportedly more common in the morning and are characteristically relieved by eating
small amounts of food. Children are more symptomatic than adults and often manifest change of appetite, both
increased and decreased. Symptoms in infants are more pronounced and consist of vomiting, diarrhea, fever, weight
loss, and irritability.
The most common serious complication of adult tapeworm infection is appendicitis. Other reported complications include
obstruction of bile ducts, pancreatic duct and tapeworm growth in ectopic locations (eg, middle ear, adenoid tissue,
uterine cavity). A mild eosinophilia of 5-15% may occur in 5-45% of patients; higher levels are rare.
Cysticercosis and neurocysticercosis
In cysticercosis, the cysticerci are most often located in subcutaneous and intermuscular tissues, followed by the eye
and then the brain. The CNS is involved in 60-90% of patients (ie, NCC). Most patients have more than one cyst; as
many as 200 cysts have been reported.
NCC symptoms include 3 characteristic syndromes: convulsions and/or seizures, intracranial hypertension, and
psychiatric disturbances, which may occur separately or simultaneously. Onset can be insidious (eg, elevated
intracranial pressure) or abrupt (eg, floating cysticerci suddenly block cerebrospinal fluid [CSF]).
Convulsions and/or seizures: Seizures are caused by the localization of cysticerci in brain parenchyma. Children most
often present with seizures, which are focal with acute onset. Cysticercosis is the most common cause of epilepsy in
endemic areas and is the sole manifestation in as many as one third of patients.
Intracranial hypertension: This is caused by obstruction of CSF by intraventricular brain cysts. Symptoms include
headache, nausea, vomiting, vertigo, and papilledema.
Psychiatric disturbances: Although changes in personality and mental status occur more often in adults than in children,
behavioral changes and learning disabilities were reported in a study of 25 affected children.
Other possible infections
Ocular cysticercosis: The subretinal space, vitreous, and conjunctiva are the most frequent sites of infection. Common
manifestations of infection include severe pain and blurred or lost vision.
Muscular and dermatologic cysticercosis: Cysticerci in muscles often are associated with NCC. Any muscle mass may be
involved and appear as acute myositis. However, most patients are asymptomatic. Subcutaneous nodules may be
Coenurosis: Clinical manifestations are determined by the site of the coenurus larvae. Patients with cerebral coenurosis
can present with seizure or intracranial hypertension. Ocular coenurosis manifests as a red and painful eye.
Neurocysticercosis is the most common parasitic infection of the central nervous system. Tissue-invading larval forms of
the pork tapeworm Taenia solium cause the disease. Historically, neurocysticercosis was endemic to only Latin America,
Asia, and Africa, although it has become increasingly frequent in the United States since the 1980s. Because of this
epidemiologic change, all general pediatricians should become familiar with its disease process.
The eggs are found in human feces because humans are the only definitive hosts. Greatest risk to infection occurs in
regions where plants in gardens or farms are fertilized with human feces and humans are exposed to contaminated soil.
In the central nervous system, T solium is deposited in the cerebral parenchyma, meninges, spinal cord, and eyes.
Unless large numbers of cysts are present, the body's immune system does not act to destroy the organism, and cysts
can live for many years undetected. A live cyst can go undetected for as long as 5 years before dying or causing
symptoms in the host.
Neurologic symptoms arise when the encysted worm dies and the human mounts an associated inflammatory response.
If the cyst lodges in the ventricular system (especially the fourth ventricle), hydrocephalus can occur.
The most characteristic feature in children is the acute onset of focal seizures.
Approximately 65-80% of children diagnosed with neurocysticercosis present with seizures, most often focal in nature.
Neurocysticercosis is endemic in certain communities because of poor sanitation, use of sewage for fertilizer, and lack of
controlled pens for pigs.
Cysticercosis, a tissue infection that involves larval cysts of the cestode Taenia solium (the human pork tapeworm),
results from the ingestion of food (especially vegetables) and water contaminated with human feces that contain T
Although infections with Taenia tapeworm cysts may involve many parts of the body, the most common site of severe
symptomatic infection is the CNS.
Neurocysticercosis, the most common parasitic disease of the CNS, is the most common cause of adult-onset epilepsy in
many of the countries where the infection is endemic.
In the stomach, oncospheres are liberated following digestion of the eggs' coats. Oncospheres invade and cross the
intestinal wall, enter the bloodstream, and then migrate to and lodge in tissues throughout the body, where they produce
small (0.2-0.5 cm) fluid-filled bladders containing a single juvenile-stage parasite (protoscolex).
Although the cysticerci may infect any organ of the body (most often the eye, skeletal muscle, and CNS), serious
disease almost exclusively involves the CNS and heart.
Oncospheres that invade the brain may lodge in the brain parenchyma, subarachnoid space, ventricular space, or
spinal cord. Cysticerci develop after 2 months and may or may not stimulate an appreciable inflammatory response.
Seizures, hydrocephalus, blindness, strokes, meningitis, encephalitis, irreversible brain damage, myositis, and
myocarditis may occur. Death may subsequently occur
Worldwide, an estimated 50,000 people die from cysticercosis each year because of CNS or cardiac complications.