Tænia saginata / Cysticercus bovis
Taeniasis is an intestinal infection caused by 3 species of tapeworm: Taenia solium (pork tapeworm), Taenia saginata(beef tapeworm) and Taenia asiatica.
Humans can become infected with T. saginata or T. asiatica when they consume infected beef meat or pig liver tissue, respectively, which has not been adequately cooked, but taeniasis due to T. saginata or T. asiatica has no major impact on human health.
Taenia saginata is a flatworm (Class Cestoda, Order Cyclophyllidea, Family Taeniidae) with a two-stage life cycle: adult (in the definitive host) and larval (in the intermediate host ). It lives in the human small intestine, usually just a single specimen at a time. It is in the form of a long segmented ribbon up to several metres in length (4 to 10 m), yellowish-white, thin at its front end and widening gradually toward the rear end.
The adult worm consists of three parts: the scolex (head), which has the appearance of a small bulge 1 to 2 mm in diameter, with four suckers and no hooks; the neck, a tapered portion joining the scolex to the rest of the body and ending with the strobila, made up of a chain of segments or rings called proglottids each measuring between 5 and 20 mm long. The older, mature proglottids towards the end of the strobila are just sacs containing from 50,000 to 80,000 embryonated eggs or embryophores.
Humans, the only known definitive host of T. saginata, are the only source of dissemination of embryophores in the environment. Eggs ingested by cattle (the intermediate hosts) hatch in the digestive tract, releasing the hexacanth embryos (oncospheres). These pass through the intestinal mucosa and migrate via general circulation to the skeletal muscles and heart, where they develop into cysticerci larvae (metacestodes) called Cysticercus bovis
Sources of infection
The source of the infection to humans has its origin in the cysticerci contained in beef. In Europe, the prevalence of bovine cysticercosis is thought to vary between 0.007% and 6.8%.
For cattle, the only source of the infection is infected humans spreading the embryophores in the environment. Up to 500,000 eggs can be released per day, and are likely to remain viable for weeks or even months in the external environment. The embryophores found in sewage sludge are in principle inactivated by the various treatment processes.
The environmental risk therefore comes from the lack or poor quality of sanitation, dispersion of septic tank sludge on pastures or fields, or defecation of hikers or campers. In addition, embryophores can be dispersed in the environment when rivers overflow.
Taeniasis caused by T. saginata is defined as a zoonosis. Consumption of raw or undercooked beef containing cysticerci is the only route of transmission to humans.
Nature of the disease
The majority of cases are strictly asymptomatic. The infection is most often recognised by the presence of proglottids in faeces and sometimes by perianal discomfort when releasing proglottids