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The cestode Taenia asiatica (Asian tapeworm) (along with T. saginata [beef tapeworm] and T. solium [pork tapeworm]) causes intestinal taeniasis in infected humans. Taenia asiatica is limited to Asia and is seen mostly in the Republic of Korea, China, Taiwan, Indonesia, and Thailand. Genetic studies by Eom et al. (2009) indicated that T. asiatica occurs in Japan, the Philippines, and Vietnam as well (T. saginata and T. solium have a worldwide distribution). (Centers for Disease Control Parasites and Health website) Genetically, T. asiatica is far more similar to T. saginata (to which it is also morphologically very similar) than it is to T. solium (Jeon et al. 2007; Eom et al. 2009). Taenia asiatica shares its intermediate host association (i.e., pigs) with T. solium, not with its closer relative T. saginata (which use cattle as the intermediate host). Thus, it appears that the divergence of T. asiatica and T. sagitata was associated with a host shift.
Humans are the only definitive host (i.e. the host that harbors adult parasites) for Taenia asiatica (as well as for T. saginata, and T. solium). An infection usually involves just a single tapeworm (Nakao et al. 2010). Eggs or gravid proglottids (bisexual reproductive segments) are passed with feces; the eggs can survive for days to months in the environment. Pigs become infected by ingesting vegetation contaminated with eggs or gravid proglottids. In the animal's intestine, the oncospheres hatch, invade the intestinal wall, and migrate to the striated muscles, where they develop into cysticerci. A cysticercus can survive for several years in the animal. Humans become infected by ingesting raw or undercooked infected meat. In the human intestine, the cysticercus develops over several months into an adult tapeworm, which can survive for years. The adult tapeworm attaches to the small intestine by its scolex and resides in the small intestine. The adults produce proglottids which mature, become gravid, detach from the tapeworm, and migrate to the anus or are passed in the stool (several per day). The eggs contained in the gravid proglottids are released after the proglottids are passed with the feces. (Centers for Disease Control Parasites and Health website)
Conlan et al. (2009) explored the role of interspecific competition among Taenia species in modulating T. solium infection of humans. In Southeast Asia, T. solium faces competition in both the definitive host (humans) and the intermediate host (pigs). In humans, adult worms of T. solium, T. saginata and T. asiatica compete through density-dependent crowding mechanisms. In pigs, metacestodes of T. solium, T. hydatigena and T. asiatica compete through density-dependent immune-mediated interactions. Humans are the definitive host for T. asiatica, T. saginata and T. solium. Pigs are the known intermediate host for T. asiatica, T. solium and T. hydatigena. Canines are the definitive host for T. hydatigena and bovines are the intermediate host for T. saginata. Conlan et al. (2009) compared the biological characteristics of T. solium, T. saginata, T. asiatica, and T. hydatigena. (Conlan et al. 2009 and references therein)