Experimental infection in a human subject by a possibly undescribed species of Taenia in Taiwan

Taenia asiatica: Historical overview of taeniasis and cysticercosis with molecular characterization

Asian Taenia is a human-infecting Taenia tapeworm known as Taenia asiatica following morphological examination of adult and larval stages of the tapeworm by Eom and Rim (1993). The life cycle of T. asiatica differs from that of T. saginata in its intermediate host (pigs versus cattle) as well as in the infected organs (liver versus muscle). T. asiatica can be differentiated from T. solium and T. saginata by examination of morphological characteristics such as the scolex, mature and gravid proglottids in the adult stage, and the scolex and bladder surface in the larval stage. T. asiatica has been identified in Korea, Taiwan, the Philippines, China, Thailand, Indonesia, Vietnam, Japan, Lao PDR, Nepal and India. The molecular tools employed for T. asiatica identification have been developed to differentiate T. asiatica from other human-infecting Taenia tapeworms based on genetic information such as nucleotide sequence of mitochondrial genes, nuclear ribosomal genes and nuclear genes that lead to development of the subsequent molecular techniques, such as PCR-RFLP, PCR-RAPD, BESST-base, LAMP and qPCR. Investigation of the phylogenetic relationships among human Taenia species revealed that T. asiatica is a sister species with T. saginata, which is genetically more similar than other Taenia species in terms of the nucleotide sequences of cox1, nad1 and 28S rDNA. The mitochondrial genomes of human Taenia tapeworms comprise 13,703bp (T. asiatica), 13,670bp (T. saginata) and 13,709bp (T. solium), and contain 36 genes including 12 protein-coding genes, 2 ribosomal RNAs (rRNAs, a small and a large subunit), and 22 transfer RNAs (tRNAs). Sequence differences in the full genome of T. asiatica and T. saginata mitochondria is 4.6%, while T. solium differs by 11%. Hox gene orthology in T. asiatica was established by comparative analysis with Platyhelminthes Hox genes. T. asiatica Hox revealed six Hox orthologs including two lab/Hox1, two Hox3, one Dfd/Hox4 and one Lox/Lox4. Hybridization between T. asiatica and T. saginata was definitely observed in these species which are sympatrically endemic in the regions of Korea, Thailand, China and Lao PDR. Comparative analyses of T. asiatica, T. saginata and T. solium genomes were also reported with genome features. Taenia asiaticus nomen novum was proposed for T. asiaticaEom and Rim, 1993 which is a homonym of T. asiatica Linstow, 1901 (Davaineidae).

Taenia saginatataeniosis: copro-antigen time-course in a voluntary self-infection

Human taeniosis due toTaenia saginatais cosmopolitan where beef is consumed; however, there is little or no information on the symptomatology over the early time-course of human infection. Copro-antigen detection is very useful in community screening for human taeniosis, particularly forT. solium, but there are no data on copro-antigen detection in pre-patent infection. In order to provide insight into this, a voluntary self-infection withT. saginatawas undertaken and monitored over a 6-month period using a copro-antigen enzyme-linked immunosorbent assay (ELISA) that we developed using anti-T. saginataantibody based reagents. Tapeworm patency, defined as first proglottid appearance, occurred on day 86 post-infection (pi) and was followed by almost daily release of proglottids (range 1–8) until termination using praziquantel on day 180 pi. The first 10 weeks post-infection (wpi) were essentially asymptomatic, followed by main symptoms of involuntary proglottid discharge throughout the infection period, and abdominal discomfort peaking around 15–19 wpi. Copro-antigens could not be reliably detected until 2 weeks before proglottid patency but then remained highly elevated over the next 15 weeks until treatment. Copro-antigen levels reverted to negative 4 days post-treatment. This time-course study suggests that although copro-antigen ELISA is an excellent diagnostic tool for established patent infections ofT. saginata, it may not be reliable for faecal antigen detection in the early infection phase prior to proglottid release forT. saginataand other human taenioses.

Lights and shadows of the Taenia asiatica life cycle and pathogenicity

Humans are definitive hosts of two well-known species of the Taenia genus, Taenia solium (the pig tapeworm) and Taenia saginata (the cattle tapeworm). In the 1990s, a third species, Taenia asiatica, was discovered, sharing features with the other two since the adult morphology is similar to that of T. saginata, but its life cycle is like that of T. solium. Human taeniasis usually is asymptomatic or displays mild symptoms, and only T. solium can cause other sometimes serious disorders when humans accidentally ingest the eggs and develop the larval stage in different organs (cysticercosis). In this review, we expose what we currently know (lights) and what we do not yet know (shadows) about the life cycle and pathogenicity of T. asiatica. Concerning its life cycle, the main uncertainty is whether humans can act as intermediate hosts of this species. We also suggest that due to its small size and location in pigs, the cysticerci probably escape veterinary inspection becoming a silent parasite. Concerning pathogenicity, it is still not known if T. asiatica can cause human liver cysticercosis, taking into account its principal hepatic tropism in pigs. To answer all these questions it would be essential to perform sensitive as well as specific diagnostic techniques for T. asiatica in humans and pigs. Currently, only molecular methods are able to determine the Taenia species, since morphology and immunology are useless, but unfortunately although largely used in research those methods are not employed in routine diagnosis.

Epidemiology and genetic diversity of Taenia asiatica: a systematic review

Taenia asiatica has made a remarkable journey through the scientific literature of the past 50 years, starting with the paradoxical observation of high prevalences of T. saginata-like tapeworms in non-beef consuming populations, to the full description of its mitochondrial genome. Experimental studies conducted in the 1980s and 1990s have made it clear that the life cycle of T. asiatica is comparable to that of T. saginata, except for pigs being the preferential intermediate host and liver the preferential location of the cysts. Whether or not T. asiatica can cause human cysticercosis, as is the case for Taenia solium, remains unclear. Given the specific conditions needed to complete its life cycle, in particular the consumption of raw or poorly cooked pig liver, the transmission of T. asiatica shows an important ethno-geographical association. So far, T. asiatica has been identified in Taiwan, South Korea, Indonesia, the Philippines, Thailand, south-central China, Vietnam, Japan and Nepal. Especially this last observation indicates that its distribution is not restricted to South-East-Asia, as was thought so far. Indeed, the molecular tools developed over the last 20 years have made it increasingly possible to differentiate T. asiatica from other taeniids. Such tools also indicated that T. asiatica is related more closely to T. saginata than to T. solium, feeding the debate on its taxonomic status as a separate species versus a subspecies of T. saginata. Furthermore, the genetic diversity within T. asiatica appears to be very minimal, indicating that this parasite may be on the verge of extinction. However, recent studies have identified potential hybrids between T. asiatica and T. saginata, reopening the debate on the genetic diversity of T. asiatica and its status as a separate species.

Immunological characteristics of patients infected with common intestinal helminths: results of a study based on reverse-transcriptase PCR

To determine whether common helminth infections could modify the intestinal immunopathological status of the host, the expression in the human duodenal mucosa of cytokines, eosinophil- and mast-cell-specific molecules and monosaccharide transporters of the glucose-transporter (GLUT) family was explored. The 31 subjects were all patients at the gastro-intestinal disease unit of Nongkhai Hospital, Thailand. Four of the 10 patients who presented with eosinophilia (> or = 6.0% of their leucocytes were eosinophils), and five of the other 21 patients, had intestinal infections with helminths when they presented or within the previous 3 months. Studies based on semi-quantitative, reverse-transcriptase PCR revealed that the interleukin-5/interferon-gamma ratio was significantly higher in the noneosinophilic, helminth-infected patients than in the non-eosinophilic, uninfected patients, whereas the IgE receptor type I (Fc epsilon RI)/mast-cell tryptase ratio was significantly higher in the eosinophilic, helminth-infected patients than in the eosinophilic, uninfected patients. Expression of Charcot-Leyden-crystal protein, GLUT-1 and GLUT-5, however, showed no significant inter-group differences. Principal-components analysis of the data on eosinophils, interleukin-5, interferon-gamma, Fc epsilon RI and mast-cell tryptase revealed that one principal component could discriminate the patients who had helminth infection from the non-eosinophilic, uninfected patients, but not from the eosinophilic, uninfected patients. These results indicate that, whatever the intestinal pathology, patients infected with common intestinal helminths tend to develop a mucosal immunological response of the Th2 type.

Intestinal cestodes

PURPOSE OF REVIEW

This review summarizes the biology, clinical aspects, diagnosis, treatment and epidemiology for the common and rarer (zoonotic) intestinal cestodes of humans.

RECENT FINDINGS

Mass drug application to eliminate Taenia solium carriers may have only temporary effects on cysticercosis transmission. At least two major world genotypes of T. solium have been identified and greater genetic heterogeneity may occur at the regional level. A new human taeniid T. asiatica has been confirmed which occurs sympatrically with T. saginata and T. solium in Southeast Asia. Coproantigen and PCR tests for Taenia spp. have greatly improved diagnostic efficacy and epidemiological studies. There appears to be an increase in human diphyllobothriasis in Europe, Japan and the Americas.

SUMMARY

Human intestinal cestode infections are globally primarily caused by species in three genera: Taenia, Hymenolepis or Diphyllobothrium. Sporadic zoonotic infections caused by nontaeniids are usually food-borne or due to accidental ingestion of invertebrate hosts. Intestinal cestode infections generally result in only mild symptoms characterized chiefly by abdominal discomfort and diarrhoea. Most human intestinal cestode infections can be treated with a single oral dose of praziquantel or niclosamide.

Development of Taenia saginata asiatica metacestodes in SCID mice and its infectivity in human and alternative definitive hosts

Development of Taenia saginata asiatica metacestodes in SCID mice, and its infectivity in humans, golden hamsters, and Mongolian gerbils as alternative definitive hosts, were investigated. Cysticerci were recovered from SCID mice that were subcutaneously injected with hatched oncospheres of T. s. asiatica. The morphological changes of metacestodes were observed. The recovered cysticerci were fed to gerbils, hamsters and humans, to check for their infectivity. Tapeworms were recovered from gerbils and hamsters fed with 20 to 45 week-old cysticerci, and proglottids excretions were observed in human volunteers fed with 45 week-old cysticerci. However, no tapeworms were recovered from gerbils fed with 10 week-old cysticerci. Our results suggest that T. s. asiatica oncospheres needed more than 20 weeks to develop to maturity in SCID mice to be infective to both their natural and alternative definitive hosts.

Epidemiological understanding of Taenia tapeworm infections with special reference to Taenia asiatica in Korea

In endemic areas of Taenia tapeworms in Korea, most of the reports showed that T. saginata was dominant over T. solium, but eating pigs is the dominant habit over eating cattle. Why do they have more T. saginata despite lower consumption of beef? This problem actually has long been recognized but until recently there has been no intensive trial to give a scientific explanation on this epidemiological enigma. By summing up the data published between the years 1963 and 1999, the ratio of armed versus unarmed tapeworms in humans was estimated at approximately 1:5. The ratio of pig-eaters versus cattle-eaters, however, was approximately 5:1. This inconsistency could be explained with the recently described T. asiatica, which infects humans through the eating of pig's viscera. We re-evaluate the importance of the consumption of visceral organ of pigs. leading us to an improved epidemiological understanding of the T. asiatica infection together with co-existing T. saginata and T. solium in Korea.

Purification of first-stage larvae of Elaphostrongylus cervi (Nematoda: Protostrongylidae) from feces

Parasites are often found in a milieu that requires extensive preparation and labor-intensive cleaning before they are suitable for use in analytical procedures. Application of modern techniques in immunology and molecular biology demands pure yields of parasites. To purify first-stage (L1) larvae of Elaphostrongylus cervi, fecal suspensions from an infected red deer were processed by the Baermann method and embedded in a gel matrix with the objective of selectively trapping fecal debris. About half the number (50.9%) of embedded larvae migrated out of the gel within a 24-hr period and were collected as clean parasite suspensions, virtually free from fecal debris. The numbers of L1 emigrating from gels were inversely proportional to the fecal debris content and the thickness of the gel. Removal of fecal debris from Baermann fluid by sieving prior to gel embedment enhanced the yield of pure L1.

Morphological description of Taenia saginata asiatica (Cyclophyllidea: Taeniidae) from man in Asia

In order to clarify the taxonomic status of the Taenia saginata-like tapeworm in East Asia, the morphological characteristics of the adult and cysticercus of classical T. saginata (American, Swiss and Poland strains) and the Taiwan Taenia were compared in the present study. The morphologic characteristics of these two parasites are very similar. The protoscolex of cysticercus of the Taiwan Taenia has a sunken rostellum while that of classical T. saginata has only an apical pit. In addition, the rostellum of the Taiwan Taenia cysticercus is usually surrounded by two rows of rudimentary hooklets. However, this structure is rarely found in classical T. saginata. Based on the results of molecular studies and morphological characteristics, the T. saginata-like tapeworm in East Asia represents a subspecies of T. saginata, named T. saginata asiatica.

Morphologic descriptions of Taenia asiatica sp. n

Among taeniid tapeworms infecting humans through pork or beef, Taenia solium Linnaeus 1758 and Taenia saginata Goeze 1782 have already been known. Based on the morphologic characteristics of adult and metacestodes of Asian Taenia saginata, the third kind of human taeniid tapeworm known to distribute in Asian countries, a new species name of Taenia asiatica is proposed. In addition to the known biology in their intermediate hosts, T. asiatica was different morphologically from Taenia saginata Goeze 1782 in having the unarmed rostellum on the scolex of adult, the large number of 'uterine twigs' and the existence of 'posterior protuberance'. These structures in the gravid proglottids were used as taxonomic keys in taeniid tapeworms for the first time. T. asiatica metacestode (Cysticercus viscerotropica) was different morphologically from T. saginata metacestode (Cysticercus bovis) in having wartlike formations on the external surface of the bladder wall.

Experimental infection of pigs and cattle with eggs of Asian Taenia saginata with special reference to its extrahepatic viscerotropism

Asian Taenia saginata, tentatively called Taenia saginata taiwanensis, has been described to be infected in its metacestode stage only in the liver of intermediate host animals. Experimentally, however, we found that the metacestodes of the Asian Taenia saginata are also infected in other viscera than the liver of pigs (Landrace-Duroc-Hampshire) 4 days to 4 months postinoculation (PI). Viscerotropism of cysticercosis was apparent because a majority (70.7%) of the non-calcified cysticerci were found in the livers while a minority were found in extrahepatic organs such as the omentum (19.2%), lungs (8.1%) and serosa of colon (2.0%). When experimentally infected to cattle, Asian T. saginata cysticerci were also observed calcified in the livers. On the other hand, classical Taenia saginata metacestodes infected the muscles and viscera of the Holstein-Friesian cattle whereas no infection was observed in experimental pigs. Extrahepatic metacestodes of Asian T. saginata, which were obtained from an experimental pig were confirmed to be infective to a male volunteer. This extrahepatic viscerotropism of Asian T. saginata metacestodes in experimental pigs explains well the transmission modes of Asian T. saginata among people considering the eating habits.

Clinical manifestations of taeniasis in Taiwan aborigines

From 1974 to 1989, a total of 24,500 aborigines at 67 villages in ten mountainous districts/towns in Taiwan were examined for the Taiwan Taenia infection and 12% were found to be infected. In order to define the clinical manifestations of taeniasis caused by the Taiwan Taenia, 1661 aborigines in ten mountainous districts were surveyed. The overall clinical rate was 76%. The clinical rate was highest among Atayal aborigines (81%), followed by Bunun (66%) and Yami (61%) aborgines and lowest among Ami aborigines (40%). Among 1153 infected people, 10% had passed gravid segments in the faeces for less than 1 year, 24% for 1-3 years, 17% for 4-5 years, 23% for 6-10 years, 16% for 11-20 years, 7% for 21-30 years, and 3% over 30 years. Twenty-six occurrences of gastrointestinal and neurological symptoms were reported by 1258 infected persons. Passing proglottides in the faeces (95%) was the most frequent sign, followed by pruritus ani (77%), nausea (46%), abdominal pain (45%), dizziness (42%), increased appetite (30%), headache (26%), etc.

Eating habits of East Asian people and transmission of taeniasis

In order to understand the role of raw meat and viscera eating habits in the transmission of taeniasis in Asian countries, 1502 infected aborigines in ten mountainous districts/towns of six counties in Taiwan, 58 infected persons in two villages on Cheju Island, Korea, and 97 cases in Ambarita District on Samosir Island, North Sumatra, Indonesia were studied during the field surveys. All infected Taiwan aborigines had the habit of eating raw meat and viscera of wild and/or domestic animals. Among these aborigines, 73% ate wild boar, 66% flying squirrel, 65% wild goat, 56% muntjac, 49% wild rats, 46% monkey, 38% hare, 20% civet-cats, 18% weasel, 17% pheasant, 14% squirrel, 4% grouse, 1% deer, 1% snake, less than 1% bamboo partridge, less than 1% frog, less than 1% bear, less than 1% dog, and less than 1% fox. Of the 58 infected persons with Taenia on Cheju Island, Korea, 72% ate raw meat and/or viscera of pig and cattle, 19% raw pork only, and 9% raw beef only. Among 12 infected persons infected with T. saginata-like tapeworms, 7 had eaten raw pork, 2 raw beef and pork and 3 raw pork. Almost all of the 97 cases of taeniasis on Samosir Island of North Sumatra, Indonesia, had eaten only undercooked pork. Eleven of 15 cases were found to be infected with T. saginata-like tapeworms. Eating habits observed suggest an unusual way of transmission of Taenia in East Asia.