NAME: Taenia solium
CHARACTERISTICS: Taenia solium is a tapeworm of the class cestoidea, order cyclophyllidea, and family Taeniidae Footnote 1.
Adult worm: Mature worms are found only in humans. Adult worm grows to approximately 2-4 m. Scolex has 4 suckers and the rostellum has two crowns of horns. Gravid proglottids are 1 by 1 cm. The ovary consists of 2 lobes, 1 accessory lobe, and 1 genital pore. The gravid proglottids of T. solium have 12 lateral branches and no vaginal sphincter muscle.
Larvae (cysticerci): As with T. saginata, the larval stage of the T. solium is also known as Cysticercus cellulosae. Cysticerci are 8-10 mm and are encompasses in a fluid filled bladder. Cysticerci are found in the muscles of the intermediate hosts and in the brain in the case of neurocysticercosis.
Eggs: Eggs are spherical with a diameter of 30-40 μm. They have a think yellow-brown radiated shell and contain a 6 hooked embryo (oncosphere). They are morphologically indistinguishable form the eggs of Taenia saginata but, unlike the eggs of T. saginata, they are infectious to humans.
PATHOGENICITY/TOXICITY: Infection with an adult tapeworm is known as taeniasis and occurs only in humans, the sole definitive host Footnote 1, Footnote 4. Cysticercosis is caused by the larval stage of T. solium.
Cysticercosis: Larval stage can cause infection in different areas of the body Footnote 6. Carriers of T. solium are at substantial risk acquiring cysticercosis due to exposure to T.solium eggs via faeco-oral autoinfection Footnote 5. Carriers can also infect members of their household, causing cysticercosis. Subcutaneous cysticercosis is more common in Asia and Africa and presents as small nodules in the arm and chest, which gradually disappear within months or years. Muscular cysticercosis is more common and show calcifications when radiographed. Opthalmic cysticercosis is rare and is caused by cysts floating in the vitreous humour and can result in impaired vision. Neurocysticercosis is the result of infection in the central nervous system. Neurocysticercosis may be initially asymptomatic for many years and then present with varied nonspecific neurologic manifestations including headaches, confusion, ataxia, seizures, and meningismus Footnote 7. Epileptic seizures are the most common symptom; neurocysticercosis is the leading cause of adult onset epilepsy. Adverse affects occur when the cysticerci degenerate, eliciting an immune response.
HOST RANGE: Humans are the definitive host Footnote 1, Footnote 4, Footnote 9, Footnote 10. Cats, dogs and gibbons have been shown, under strict experimental conditions to be able to act as the definitive host of T. solium Footnote 11. Pigs serve as the intermediate host Footnote 4, Footnote 9, Footnote 10. Dogs are also recognised as an intermediate host Footnote 2, Footnote 12.
INFECTIOUS DOSE: Unknown.
MODE OF TRANSMISSION: The intermediate host will contract T. saginata by ingesting the eggs Footnote 1, Footnote 2. The eggs develop into the infective cysticercus in the tissues of the infected intermediate host. Humans contract Taeniasis by ingesting undercooked pork infested with T solium cysticerci.
In humans, cysticercosis occurs during an infection by the larval stage of T. solium when ova are ingested. The ova develop into larvae, penetrate the intestinal wall, disseminate throughout the body via the vascular system, and encyst in tissue as cysticerci Footnote 13. However, taeniasis occurs during an infection by the adult tapeworm of T solium when the human definitive host ingests cysticerci.
INCUBATION PERIOD: Cysticerci take 2-3 months to develop in muscle following ingestion of eggs; proglottids appear in stool within 2 months of ingestion of cysticerci Footnote 6.
COMMUNICABILITY: Humans acquire the infection through fecal oral contamination by infected individual hosting the mature adult parasite Footnote 6, Footnote 9 or by ingesting undercook pork infested with T solium cysticerci.. Autoinfection is also possible.
PHYSICAL INACTIVATION: Irradiation and cooking will inactivate the cycticerci Footnote 19. A minimum temperature of 60ºC is required for inactivation Footnote 4. Freezing at a temperature of -10ºC for 4 days will inactivate cysticerci Footnote 20.
SURVEILLANCE: Monitor for symptoms. Microscopy is used to diagnose taeniasis by visualization of eggs and proglottids in faeces Footnote 6. However, excretion is intermittent and usually stool examination for eggs or parasites are negative. Cysticercosis is diagnosed using serological testing such as antigen detection in serum or CSF or feces. The enzyme-linked immunoelectrotransfer blot (EITB) is used to increase the specificity Footnote 21.
FIRST AID/TREATMENT: Infection is treated with albendazole or praziquantel Footnote 5.
LABORATORY-ACQUIRED INFECTIONS: None Footnote 3.
PRIMARY HAZARDS: Ingestion of infectious eggs or cysticerci Footnote 3.
SPECIAL HAZARDS: During the identification process caution should be taken until a definitive identification as non-infectious T. saginata is not made confirmed as the eggs are morphologically identical Footnote 14. The eggs are highly infectious and remain viable within the environment for many months. Taeniasis (intestinal tapeworm) is prevented by destruction, freezing or adequate heating of cysticercotic pork. In contrast human cysticercosis results from fecal-oral contamination with material containing T. solium eggs.
RISK GROUP CLASSIFICATION: Risk Group 2.
CONTAINMENT REQUIREMENTS: Containment Level 2 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, or cultures Footnote 22.
PROTECTIVE CLOTHING: Lab coat. Gloves when direct skin contact with infected materials or animals is unavoidable. Eye protection must be used where there is a known or potential risk of exposure to splashes Footnote 22.
OTHER PRECAUTIONS: All procedures that may produce aerosols, or involve high concentrations or large volumes should be conducted in a biological safety cabinet (BSC). The use of needles, syringes, and other sharp objects should be strictly limited. Additional precautions should be considered with work involving animals or large scale activities Footnote 22.
SPILLS: Allow aerosols to settle and, wearing protective clothing, gently cover spill with paper towels and apply an appropriate disinfectant, starting at the perimeter and working towards the centre. Allow sufficient contact time before clean up Footnote 22.
DISPOSAL: Decontaminate all wastes that contain or have come in contact with the infectious organism by autoclave, chemical disinfection, gamma irradiation, or incineration before disposing Footnote 22.
STORAGE: The infectious agent should be stored in leak-proof containers that are appropriately labelled Footnote 22.
UPDATED: December 2011
PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada.
Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Public Health Agency of Canada, 2011