Tapeworms and Their Lifecycle

Learning Outcomes

• The outcomes of the lesson are to explain the morphology, life cycle, pathogenesis/disease, and treatment & prevention of Taenia saginata and Taenia solium.

Cyclophyllidean Larvae

• Cyclophyllidean larvae are complex and come in various forms.
• Medically important larvae include cysticercoid, cysticercus, and hydatid. Some of these larvae cause amplification of the infection.

Tapeworm Species in Humans

Taenia saginata

• T. saginata is a beef tapeworm.
• Length ranges from 6 to 30 feet.
• Cosmopolitan distribution, common in Africa and South America.
• Transmission is by ingesting the larval form in undercooked beef.
• Infection rates in North America are less than 1% of infected individuals. This can be higher in some third-world nations
• Symptoms are either absent or mild abdominal discomfort.
• Diagnosis involves finding eggs or proglottids in feces.

Taenia solium

• T. solium is a pork tapeworm.
• The scolex has four suckers and a double crown of hooks.
• It has a narrow neck and a large strobila (consisting of hundreds of proglottids).
• Proglottids release 50-60,000 eggs and detach from the distal end, excreted in feces.
• Infection develops about 2 months after ingestion.

Taenia Life Cycle

• Humans are the definitive host.
• Eggs can survive in the environment for days to months.
• Adult worms attach to the human small intestine.
• Proglottids pass with feces.
• Autoinfection can occur if people ingest eggs.

Taenia solium Transmission

• T. solium is endemic in less-developed countries where pigs are raised for food.
• Common in Latin America, Asia, Sub-Saharan Africa, and parts of Oceania.
• Infection with adult T. solium produces symptoms similar to T. saginata.
• Infection involves ingesting eggs via fecal contamination.
• Ingestion of T. solium eggs or proglottids in pork can result in porcine cysticercosis.

Taeniasis

• Taeniasis is a parasitic infection.
• Caused by Taenia saginata (beef tapeworm), Taenia solium (pork tapeworm), and Taenia asiatica (Asian tapeworm).
• Humans can be infected by eating raw or undercooked contaminated meat (pork or beef).
• Signs and symptoms are mild and non-existent.
• T.solium infections can lead to cysticercosis.

Taenia Transmission

• The primary risk factor for taeniasis is the consumption of raw or undercooked beef or pork.
• Intermediate hosts (cows and pigs) become infected by contact with the worm’s eggs or proglottids in the feces of infected humans.

Symptoms of Tapeworm Infections

• Most people with tapeworm infections have no symptoms or mild symptoms.
• T. saginata tapeworms are larger (up to 10 meters) than T. solium (usually 3 meters), causing more symptoms.
• Symptoms relate to digestive issues, including abdominal pain, loss of appetite, weight loss, and upset stomach.
• The active passing of proglottids (tapeworm segments) is a noticeable symptom.

Cysticercosis

• Cysticercosis is a disease caused by the Taenia solium larval stage, cysticerci, in humans.
• Cysticerci develop in various tissues, including muscles, eyes, and brain.
• The larval form in T. solium has a thick, protective shell.
• This form penetrates the intestinal wall, circulates to muscles, and encysts in tissues.
• Cysticercosis can cause various forms of the disease, including: neurocysticercosis, muscle/subcutaneous cysticercosis, and ophthalmic cysticercosis.

Neurocysticercosis

• Neurocysticercosis affects the central nervous system.
• Symptoms include epileptic seizures, intracranial hypertension, and hydrocephalus.
• The racemose form is highly fatal.
• It involves a large, translucent cyst without a scolex.

Cysticercosis Diagnosis

• Serologic diagnosis: Antibody assays for T. solium infections using 8 kDa antigens, GP50, FAST-ELISA, antigen-detection assays (live parasites), and CSF antibodies.
• Neuroimaging: CT and MRI can show the location, number, viability, and severity of the inflammatory reaction.

Cysticercosis Treatment

• Treatment is individualized based on cyst location, inflammation levels, and clinical presentation
• Therapy includes analgesics, antiepileptic drugs, cysticidal drugs, surgical resection of lesions, and placement of ventricular shunts, as well as the use of Albendazole and Dexamethasone.
• Subarachnoid cases are treated with antiparasitic therapy.
• Dead calcified cysts do not require antiparasitic drugs.
• Symptomatic therapy.
• Surgical therapy for hydrocephalus or removal of large cysts.

Taeniasis Diagnosis

• Diagnosis is made by examining stool samples.
• Individuals should be asked about passing tapeworm segments.
• Stool samples are collected over three days and examined for eggs under a microscope.
• Tapeworm eggs can be detected 2–3 months after infection.

Prevention & Control of Taeniasis

• Avoid consuming raw or undercooked pork and beef.
• Utilize USDA recommended meat preparation guidelines.
• Maintain appropriate sanitation practices.

Following Lecture

• The next lecture will cover nematodes (roundworms).