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INTRODUCTION

Taeniasis refers to an intestinal infection with the adult stage of the beef tapeworm (Taenia saginata), the pork tapeworm (T. solium), or the Asian pork tapeworm (T. asiatica). Cysticercosis is the somatic infection with the larval stage of the pork tapeworm. Neurocysticercosis (NCC) is central nervous system infection with T. solium larvae. Both beef and pork tapeworms have been known as parasites of humans since ancient times, but infection of humans by the larval stage of the pork tapeworm was not recognized until the sixteenth century.1

LIFE CYCLE

Cestodes of the family Taeniidae complete their cycle in two mammalian hosts, typically a carnivore and an herbivore, between which a well-defined predator/prey relationship exists.1,2 Humans are the definitive hosts for three species of Taenia: T. saginata, T. solium, and T. asiatica. The larval stages infect cattle (T. saginata) and swine (T. solium and T. asiatica). The larvae of T. solium can develop in dogs and humans.3–5 Larval stages of T. asiatica are only found in pigs and it is assumed to be confined to the liver of this porcine host.6 However, its high prevalence in some countries where raw liver is not routinely consumed suggests that T. asiatica may encyst in other organs.7 The northern strain of T. saginata, reported only from northern Russia (Siberia), has a unique life cycle with larvae encysted in the muscles and cerebral meninges of reindeer. The transmission cycle of this strain is maintained by the local custom of eating raw reindeer brain.8

Humans contract taeniasis through the ingestion of infective cysticerci in raw or undercooked beef, pork, or dog meat (Fig. 130-1).2 In the small intestine, the cysticercus inserts its scolex to attach to the mucosa and develops into the adult worm, which can survive for up to 30 years in the human intestine. Usually one tapeworm is present, but up to 25 have been reported from a single host.9 Adult T. saginata usually measure 4–12 meters in length, but may reach lengths up to 25 meters, while T. solium grows to lengths of between 2 and 8 meters.10 Release of segments containing eggs infective for the intermediate host begins in the human intestine after 10–12 weeks for T. saginata, 5–12 weeks for T. solium, and 8–17 weeks for T. asiatica.6,9 A single gravid proglottid may contain between 1000 and 2000 eggs for T. saginata, 1000 eggs for T. solium and approximately 700 eggs for T. asiatica.10 A tapeworm carrier releases between six and nine proglottids daily.

FIGURE 130-1

Cysticerci, larval forms of T. solium, in “measly” pork. (Source: Dr. Green/CDC.)

Cysticercosis is caused by ...

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