Definition. Taeniasis is the intestinal infection caused by 3 adult species of tapeworm: Taenia saginata (beef tapeworm), Taenia solium (pork tapeworm) and Taenia asiatica. Humans are the only definitive hosts for T. saginata and T. solium.
Background. Taenia saginata (the beef tapeworm) — also known as Taeniarhynchus saginatus — and Taenia solium (the pork tapeworm) adults normally live only in the human gut. Both parasites are long-lived and have a worldwide distribution. T. saginata can grow to the length of 10 m and T. solium 6 m and both are normally found within the small intestine.
Morphology. Taenia species measure from roughly 15 cm up to many meters in length (T. saginata). Their scolex is devoid of a rostellum. A ring of scolex hooks between the four suckers is composed of alternately arranged hooks of two different sizes and shapes. Their number, size, and shape are important characteristics for identification. The male genital organs consist of the testes (70–1200, depending on the species) distributed among the longitudinal excretory vessels, the vas deferens leading from the middle to the lateral part of the proglottid, ending with a cirrus pouch with a cirrus at the lateral margin of the proglottid. The female organs comprise a bipartite ovary, behind which is a compact vitellarium, and a vagina parallel and posterior to the vas deferens, stretching to the lateral margin. In gravid proglottids, its anterior branches penetrate beyond the border of the anterior proglottid, leaving holes when the mature segment is detached. The number of eggs in each segment is 10,000–100,000 depending on the species. They are round to oval in shape, spherical, and measure 25–35 μm. They are protected by an “embryophore” composed of blocks of brown segments of keratin-like material. Through the influence of enzymes in the stomach and duodenum, the embryophore breaks open and releases the oncosphere.
Infection and transmission. Infection with the T. solium tapeworm occurs when humans eat raw or undercooked, infected pork. Tapeworm eggs pass with the feces and are infective for pigs. Infection in humans with the T. solium tapeworm causes few clinical symptoms. However as well as being infective for pigs, T. solium eggs may also infect humans if they are ingested, causing infection with the larval parasite in the tissues (human cysticercosis). This infection can result in devastating effects on human health. The larvae (cysticerci) may develop in the muscles, skin, eyes and the central nervous system. When cysts develop in the brain, the condition is referred to as neurocysticercosis. Symptoms include severe headache, blindness, convulsions, and epileptic seizures, and can be fatal. Neurocysticercosis is the most frequent preventable cause of epilepsy worldwide and is estimated to cause 30% of all epilepsy cases in countries where the parasite is endemic.
Treatment. Taenaisis can be treated with praziquantel (5-10 mg/kg, single-administration) or niclosamide (adults and children over 6 years: 2 g, single-administration after a light meal followed after 2 hours by a laxative; children aged 2–6 years: 1 g; children under 2 years: 500 mg).
Prevention and control. To prevent, control and possibly eliminate T. solium, proper public health interventions with an approach spanning veterinary, human health and environmental sectors are required. Eight interventions for the control of T. solium can be used in different combinations designed on the basis of the context in the countries: treatment of taeniasis cases; intervention in pigs (vaccination plus anthelmintic treatment) together with strategic mass drug administration for taeniasis; health education, including hygiene and food safety; improved sanitation; improved pig husbandry; and improved meat inspection and processing of meat products.
References:
Centers for Disease Control and Prevention. Parasites – Taeniasis. [Updated:January 10, 2013]. Available from: https://www.cdc.gov/parasites/taeniasis/disease.html
Lucius R., Brigitte Loos-Frank, Richard P.L., Robert P., Craig W.R., and Richard K.G. The Biology of Parasites. Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim, German: 2017.
World Health Organization. Taeniasis/cycticercosis. [WHO; 2019]. Available: https://www.who.int/news-room/fact-sheets/detail/taeniasis-cysticercosis
