6533b821fe1ef96bd127afee

RESEARCH PRODUCT

Human cysticercosis and larval tropism of Taenia asiatica

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Taenia solium, T. saginata and the recently discovered T. asiatica1xTaiwan Taenia and taeniasis. Fan, P.C. Parasitol. Today. 1988; 4: 86–88Abstract | Full Text PDF | PubMed | Scopus (61)See all References, 2xMorphologic descriptions of Taenia asiatica sp. n.. Eom, K.S. and Rim, H.J. Korean J. Parasitol. 1993; 31: 1–6Crossref | PubMedSee all References, 3xMorphological description of Taenia saginata asiatica (Cyclophyllidea: Taeniidae) from man in Asia. Fan, P.C. et al. J. Helminthol. 1995; 69: 299–303Crossref | PubMed | Scopus (44)See all References, are species of taeniid cestodes whose adult stages are known to infect humans. Less clear is whether the eggs of T. asiatica also infect humans (as those of T. solium do, causing cysticercosis and the fatal neurocysticercosis) or whether the species is similar to T. saginata whose eggs do not cause infections in humans.Although evidence does exist in support of infective egg stages4xCysticercosis in Asian-Pacific regions. Ito, A. Parasitol. Today. 1992; 8: 182–183Abstract | Full Text PDF | PubMed | Scopus (17)See all References, 5xTaeniasis/cysticercosis in Indonesia as an emerging disease. Simanjuntak, G.M. et al. Parasitol. Today. 1997; : 321–323Abstract | Full Text PDFSee all References, it is also disputed for two main reasons6xGenetic characterization of the Asian Taenia, a newly described taeniid cestode of humans. Bowles, J. and McManus, D.P. Am. J. Trop. Med. Hyg. 1994; 50: 33–44PubMedSee all References, 7xAsian (Taiwan) Taenia: species or strain?. McManus, D.P. and Bowles, J. Parasitol. Today. 1994; 10: 273–275Abstract | Full Text PDF | PubMed | Scopus (20)See all References, 8xFailure of experimental infection of baboons (Papio hamadryas) with the eggs of Asian Taenia. Fall, E.H. et al. J. Helminthol. 1995; 69: 367–368Crossref | PubMed | Scopus (2)See all References. First, T. asiatica is more closely related to T. saginata at the molecular level than to any other taeniid; if T. saginata does not cause human cysticercosis, then the same could be said of T. asiatica. Second, observations of human populations where T. asiatica adults are highly prevalent show no evidence of human cysticercosis or neurocysticercosis (eg. Taiwan, and Samosir Island, Indonesia). We would like to discuss further reasons why such observations might be incorrect.First, although molecular affinities between T. asiatica and T. saginata are very close, the egg infectivity of the two species is quite different; the natural hosts of T. saginata are cattle, while those of T. asiatica are pigs (the same intermediate host for human cysticercosis-producing T. solium). Second, the absence of cysticercosis or neurocysticercosis in these human populations may merely suggest a low prevalence of T. solium. We, however, believe that it is an erroneous indicator of whether the eggs of T. asiatica can infect humans.So, are there similarities between T. solium and T. asiatica that could be used to indicate whether eggs of T. asiatica infect humans? Again, subtle differences between the two species suggest that this is not the case. First, tropism and size of the larval forms differ between the two species. The larva of T. solium (Cysticercus cellulosae) in pigs exhibits no defined tropism9xExperimental infection of an isolate of Taenia solium from Hainan in domestic animals. Fan, P.C. et al. J. Helminthol. 1994; 68: 265–266Crossref | PubMed | Scopus (11)See all References9 and larval size ranges from 5 to 15 mm (Ref. 10xMorphological types of Taenia solium cysticerci. Rabiela, M.T. et al. Parasitol. Today. 1989; 5: 357–359Abstract | Full Text PDF | PubMed | Scopus (21)See all References10). In contrast, the larva of T. asiatica (C. viscerotropica) in the pig (and other experimental intermediate hosts such as calves, goats and monkeys)1xTaiwan Taenia and taeniasis. Fan, P.C. Parasitol. Today. 1988; 4: 86–88Abstract | Full Text PDF | PubMed | Scopus (61)See all References, 11xStudies on taeniasis in Taiwan. VI. Is Taenia saginata from Taiwan, Korea and Indonesia a new species?. Fan, P.C. et al. Chinese J. Parasitol. 1988; 1: 56–70See all References, exhibits marked liver tropism, while reaching a larval size of approximately 2 mm1xTaiwan Taenia and taeniasis. Fan, P.C. Parasitol. Today. 1988; 4: 86–88Abstract | Full Text PDF | PubMed | Scopus (61)See all References, 2xMorphologic descriptions of Taenia asiatica sp. n.. Eom, K.S. and Rim, H.J. Korean J. Parasitol. 1993; 31: 1–6Crossref | PubMedSee all References. This suggests that if C. viscerotropica follows the same developmental course in humans as in other intermediate hosts, then it would preferentially parasitize the liver, causing hepatic cysticercosis, with smaller larvae being present than if C. cellulosae were the infective agent. Such cases of hepatic cysticercosis could be symptomatic or not, depending on larval number and location within the liver (although hepatic/gastrointestinal manifestations may occur). It could be assumed that such clinical symptoms would be more related to the initial stages of cystic hydatidosis than to the classical cysticercosis or neurocysticercosis caused by T. solium. Therefore, where T. asiatica is prevalent in human populations, the absence of classical evidence of cysticercosis should not be taken as indication of the lack of human cysticercosis caused by this parasite.The clinical risk of this possible larval parasitization by T. asiatica could be similar to that of classical cysticercosis, but only if the larvae also reach other locations within humans (as in the case of T. solium and the larvae of Echinococcus granulosus or E. multilocularis) or develop aberrant forms as in the case of T. solium (the racemose cysticercus). At the experimental level, larvae of T. asiatica have been successfully developed in nonhepatic regions12xExperimental infections of pigs and cattle with eggs of Asian Taenia saginata with special reference to its extrahepatic viscerotropism. Eom, K.S. et al. Korean J. Parasitol. 1992; 30: 269–275CrossrefSee all References12 and can develop larger body sizes in hosts other than pigs13xHuman Taenia eggs develop into cysticerci in SCID mice. Ito, A. et al. Parasitology. 1997; 114: 85–88Crossref | PubMed | Scopus (24)See all References13.Evidence for the infection of humans by eggs of T. asiatica therefore remains contradictory. However, we are of the opinion that C. viscerotropica should be included in the evaluation of liver lesions compatible with the larval development of cestodes, particularly in those Asian countries where the parasite is already known to occur.