Current Status of Taeniasis in Thailand

Taeniasis is prevalent in all regions of Thailand, except the South. Infections were more frequently found in males than females of any age from 7-83 years. Taenia saginata is the most common species throughout the country. Taenia asiatica was reported only in the province of Kanchanaburi in the Central region. Co-infections, with Taenia solium and T. asiatica or T. solium and T. saginata, were found. Hybridization between T. asiatica and T. saginata is evidence that co-infection is never found between these 2 species. Finding more than 1 worm in a single patient was not entirely rare. Genetic variation was found without correlation to its geographic distribution in T. saginata, whereas no variation was found in T. asiatica.     

Sympatric Distribution of Three Human Taenia Tapeworms Collected between 1935 and 2005 in Korea

Taeniasis has been known as one of the prevalent parasitic infections in Korea. Until recently, Taenia saginata had long been considered a dominant, and widely distributed species but epidemiological profiles of human Taenia species in Korea still remain unclear. In order to better understand distribution patterns of human Taenia tapeworms in Korea, partial nucleotide sequences of mitochondrial cox1 and ITS2 (internal transcribed spacer 2) were determined, along with morphological examinations, on 68 Taenia specimens obtained from university museum collections deposited since 1935. Genomic DNA was extracted from formalin-preserved specimens. Phylogenetic relationships among the genotypes (cox1 haplotype) detected in this study were inferred using the neighbor-joining method as a tree building method. Morphological and genetic analyses identified 3 specimens as T. solium, 51 specimens as T. asiatica, and 14 specimens as T. saginata. Our results indicate that all 3 Taenia tapeworms are sympatrically distributed in Korea with T. asiatica dominating over T. saginata and T. solium.     

Taenia asiatica: the Most Neglected Human Taenia and the Possibility of Cysticercosis

Not only Taenia solium and Taenia saginata, but also Taenia asiatica infects humans. The last species is not included in the evaluation of the specificity of the immunodiagnostic techniques for taeniasis/cysticercosis. There is currently no specific immunodiagnostic method for T. asiatica available. Therefore, due to the fact that molecular techniques (the only tool to distinguish the 3 Taenia species) are normally not employed in routine diagnostic methods, the 2 questions concerning T. asiatica (its definite geographic distribution and its ability to cause human cysticercosis), remain open, turning T. asiatica into the most neglected agent of human taeniasis-cysticercosis.     

Infection of Taenia asiatica in a Bai Person in Dali,China

We report here a human case of Taenia asiatica infection which was confirmed by genetic analyses in Dali, China. A patient was found to have symptoms of taeniasis with discharge of tapeworm proglottids. By sequencing of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene, we observed nucleotide sequence identity of 99% with T. asiatica and 96% with T. saginata. Using the cytochrome b (cytb) gene, 99% identity with T. asiatica and 96% identity with T. saginata were found. Our findings suggest that taeniasis of people in Dali, China may be mainly caused by T. asiatica.     

Human Taeniasis in the Republic of Korea: Hidden or Gone?

History and current status of human taeniasis in the Republic of Korea, due to Taenia solium, Taenia asiatica, and Taenia saginata, are briefly reviewed. Until the 1980s, human taeniasis had been quite common in various localities of Korea. A study from 1924 reported 12.0% egg prevalence in fecal examinations. Thereafter, the prevalence of Taenia spp. ranged from 3% to 14% depending on the time and locality. Jeju-do, where pigs were reared in a conventional way, was the highest endemic area of taeniasis. An analysis of internal transcribed spacer 2 and mitochondrial cytochrome c oxidase 1 genes of 68 taeniasis cases reported from 1935 to 2005 in Korea by a research group revealed the relative occurrence of the 3 Taenia spp. as follows: T. solium (4.4%), T. asiatica (75.0%), and T. saginata (20.6%). However, national surveys on intestinal helminths conducted every 5 years on randomly selected people revealed that the Taenia egg prevalence dropped from 1.9% in 1971 to 0.02% in 1997 and finally to 0.0% in 2004. With the exception of 3 egg-positive cases reported in 2008 and 2 worm-proven cases in 2011, no more cases have been officially recorded. Based on these surveys and also on other literature, it can be concluded that taeniasis has virtually disappeared from Korea, although a few sporadic cases may remain hidden. Human cysticercosis is also expected to disappear within a couple of decades in Korea.     

State of the Art of Taenia solium as Compared to Taenia asiatica

Three species of tapeworms infect humans in their adult stage (Taenia solium, Taenia saginata and Taenia asiatica). The 3 are flat, opaque white or yellowish, and exceptional long segmented parasites, measuring 1 to 12 m in their adult stage. In this review, the development of the knowledge regarding the first species, mainly focused on understanding how the larval stage or cysticercus is transmitted to humans, is described. The second species is a cosmopolitan parasite that only causes taeniosis and not cysticercosis; therefore, it will not be included. Information on the third species, which is presently being produced, since this species was recognized as such only at the end of the 20th century, will be discussed at the end of this review.     

Four Cases of Taenia saginata Infection with an Analysis of COX1 Gene

Human taeniases had been not uncommon in the Republic of Korea (=Korea) until the 1980s. The prevalence decreased and a national survey in 2004 revealed no Taenia egg positive cases. However, a subsequent national survey in 2012 showed 0.04% (10 cases) prevalence of Taenia spp. eggs suggesting its resurgence in Korea. We recently encountered 4 cases of Taenia saginata infection who had symptoms of taeniasis that included discharge of proglottids. We obtained several proglottids from each case. Because the morphological features of T. saginata are almost indistinguishable from those of Taenia asiatica, molecular analyses using the PCR-RFLP and DNA sequencing of the cytochrome c oxidase subunit 1 (cox1) were performed to identify the species. The PCR-RFLP patterns of all of the 4 specimens were consistent with T. saginata, and the cox1 gene sequence showed 99.8-100% identity with that of T. saginata reported previously from Korea, Japan, China, and Cambodia. All of the 4 patients had the history of travel abroad but its relation with contracting taeniasis was unclear. Our findings may suggest resurgence of T. saginata infection among people in Korea.     

Historical Overview of Taenia asiatica in Taiwan

An overview of the epidemiological, biological, and clinical studies of Taenia and taeniasis in Taiwan for the past century is presented. The phenomenal observations that led to the discovery of Taenia asiatica as a new species, which differ from Taenia solium and Taenia saginata, are described. Parasitological surveys of the aborigines in Taiwan revealed a high prevalence of taeniasis, which might be due to the culture of eating raw liver of hunted wild boars. Chemotherapeutic deworming trials involving many patients with taeniasis were discussed. Praziquantel was found to be very effective, but sometimes complete worms could not be recovered from the feces after treatment, probably due to the dissolution of the proglottids. Atabrine, despite some side effects, can still be used, in properly controlled dosages, as the drug of choice for human T. asiatica infection if we need to recover the expelled worms for morphological examinations. Research results on the infection of T. asiatica eggs from Taiwan aborigines in experimental animals were also noted. Since the pig serve as the natural intermediate host of T. asiatica and the predilection site is the liver, a differential comparison of other parasitic pathogens that might cause apparently similar lesions is also presented.     

Differential diagnosis of Taenia asiatica using multiplex PCR

Taenia asiatica and T. saginata are frequently confused tapeworms due to their morphological similarities and sympatric distribution in Asian regions. To resolve this problem, a high-resolution multiplex PCR assay was developed to distinguish T. asiatica infections from infection with other human Taenia tapeworms. For molecular characterization, the species specificity of all materials used was confirmed by sequencing of the cox1 gene. Fifty-two samples were analyzed in this study, comprising 20 samples of T. asiatica genomic DNA from China, Korea, and the Philippines; 24 samples of T. saginata from Belgium, Chile, China, Ethiopia, France, Indonesia, Korea, Laos, the Philippines, Poland, Taiwan, Thailand, and Switzerland; and 10 samples of T. solium from Cape Verde, China, Honduras, and Korea. The diagnostic quality of the results obtained using PCR and species-specific primers designed from valine tRNA and NADH genes was equal to that based on the nucleotide sequencing of the cox1 gene. Using oligonucleotide primers Ta4978F, Ts5058F, Tso7421F, and Rev7915, the multiplex PCR assay was useful for the differentially diagnosing T. asiatica, T. saginata, and T. solium based on 706-, 629-, and 474-bp bands.     

Genetic Variation of Taenia Pisiformis Collected from Sichuan,China, Based on the Mitochondrial Cytochrome b gene

Taenia pisiformis is one of the most important parasites of canines and rabbits. T. pisiformis cysticercus (the larval stage) causes severe damage to rabbit breeding, which results in huge economic losses. In this study, the genetic variation of T. pisiformis was determined in Sichuan Province, China. Fragments of the mitochondrial cytochrome b (cytb) (922 bp) gene were amplified in 53 isolates from 8 regions of T. pisiformis. Overall, 12 haplotypes were found in these 53 cytb sequences. Molecular genetic variations showed 98.4% genetic variation derived from intra-region. F_ST and Nm values suggested that 53 isolates were not genetically differentiated and had low levels of genetic diversity. Neutrality indices of the cytb sequences showed the evolution of T. pisiformis followed a neutral mode. Phylogenetic analysis revealed no correlation between phylogeny and geographic distribution. These findings indicate that 53 isolates of T. pisiformis keep a low genetic variation, which provide useful knowledge for monitoring changes in parasite populations for future control strategies.     

Occurrence of a Hybrid Between Taenia saginata and Taenia asiatica Tapeworms in Cambodia

Human infection with Taenia asiatica or a hybrid between Taenia saginata and T. asiatica has not been reported in Cambodia. We detected for the first time a hybrid form between T. saginata and T. asiatica in Preah Vihear Province, Cambodia. An adult tapeworm specimen, i.e., 75 cm long strobila without scolex, was expelled from a 27-year-old man after praziquantel medication and purging. It was morphologically indistinguishable between T. saginata and T. asiatica. Several proglottids were molecularly analyzed to confirm the tapeworm species. The mitochondrial gene encoding cytochrome c oxidase subunit 1 (cox1) and nuclear genes encoding elongation factor-1α (ef1) and ezrin-radixin-moesin (ERM)-like protein (elp) were sequenced, and a single-allele analysis was performed to confirm the haploid genotype. The results revealed that our sample showed a discrepancy between the mitochondrial and 2 nuclear genes. It possessed homozygous sequences typical of T. saginata at cox1 and ef1 loci. However, it was heterozygous at the elp locus, with 1 allele in T. asiatica (elpA) and 1 in T. saginata (elpC), which indicates that it is a hybrid between T. saginata and T. asiatica. The present results confirmed the presence of a hybrid between T. saginata and T. asiatica in Cambodia and strongly suggest the existence of also ‘pure’ T. asiatica in Cambodia.     

Phylogenetic characterisation of Taenia tapeworms in spotted hyenas and reconsideration of the “Out of Africa” hypothesis of Taenia in humans

The African origin of hominins suggests that Taenia spp. in African carnivores are evolutionarily related to the human-infecting tapeworms Taenia solium, Taenia saginata and Taenia asiatica. Nevertheless, the hypothesis has not been verified through molecular phylogenetics of Taenia. This study aimed to perform phylogenetic comparisons between Taenia spp. from African hyenas and the congeneric human parasites. During 2010–2013, 233 adult specimens of Taenia spp. were collected from 11 spotted hyenas in Ethiopia. A screening based on short DNA sequences of the cytochrome c oxidase subunit 1 gene classified the samples into four mitochondrial lineages designated as I–IV. DNA profiles of nuclear genes for DNA polymerase delta (pold) and phosphoenolpyruvate carboxykinase (pepck) showed that lineages II and III can be assigned as two independent species. Common haplotypes of pold and pepck were frequently found in lineages I and IV, suggesting that they constitute a single species. Morphological observations suggested that lineage II is Taenia crocutae, but the other lineages were morphologically inconsistent with known species, suggesting the involvement of two new species. A phylogenetic tree of Taenia spp. was reconstructed by the maximum likelihood method using all protein-coding genes of their mitochondrial genomes. The tree clearly demonstrated that T. crocutae is sister to T. saginata and T. asiatica, whereas T. solium was confirmed to be sister to the brown bear tapeworm, Taenia arctos. The tree also suggested that T. solium and T. arctos are related to two species of Taenia in hyenas, corresponding to lineages I + IV and III. These results may partially support the African origin of human-infecting Taenia spp., but there remains a possibility that host switching of Taenia to hominins was not confined to Africa. Additional taxa from African carnivores are needed for further testing of the “Out of Africa” hypothesis of Taenia in humans.     

Molecular Approaches to Taenia asiatica

Taenia solium, T. saginata, and T. asiatica are taeniid tapeworms that cause taeniasis in humans and cysticercosis in intermediate host animals. Taeniases remain an important public health concerns in the world. Molecular diagnostic methods using PCR assays have been developed for rapid and accurate detection of human infecting taeniid tapeworms, including the use of sequence-specific DNA probes, PCR-RFLP, and multiplex PCR. More recently, DNA diagnosis using PCR based on histopathological specimens such as 10% formalin-fixed paraffin-embedded and stained sections mounted on slides has been applied to cestode infections. The mitochondrial gene sequence is believed to be a very useful molecular marker for not only studying evolutionary relationships among distantly related taxa, but also for investigating the phylo-biogeography of closely related species. The complete sequence of the human Taenia tapeworms mitochondrial genomes were determined, and its organization and structure were compared to other human-tropic Taenia tapeworms for which complete mitochondrial sequence data were available. The multiplex PCR assay with the Ta4978F, Ts5058F, Tso7421F, and Rev7915 primers will be useful for differential diagnosis, molecular characterization, and epidemiological surveys of human Taenia tapeworms.     

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.     

Molecular Characterization of Taenia multiceps Isolates from Gansu Province,China by Sequencing of Mitochondrial Cytochrome C Oxidase Subunit 1

A total of 16 Taenia multiceps isolates collected from naturally infected sheep or goats in Gansu Province, China were characterized by sequences of mitochondrial cytochrome c oxidase subunit 1 (cox1) gene. The complete cox1 gene was amplified for individual T. multiceps isolates by PCR, ligated to pMD18T vector, and sequenced. Sequence analysis indicated that out of 16 T. multiceps isolates 10 unique cox1 gene sequences of 1,623 bp were obtained with sequence variation of 0.12-0.68%. The results showed that the cox1 gene sequences were highly conserved among the examined T. multiceps isolates. However, they were quite different from those of the other Taenia species. Phylogenetic analysis based on complete cox1 gene sequences revealed that T. multiceps isolates were composed of 3 genotypes and distinguished from the other Taenia species.     

Current Status and Perspectives of Cysticercosis and Taeniasis in Japan

This mini-review describes recent epidemiological trends in cysticercosis and taeniasis in Japan. Some of the topics discussed herein were presented at the first symposium on "Current perspectives of Taenia asiatica researches", that was held in Osong in Chungbuk Province, South Korea, in October 2011 and organized by Prof. K. S. Eom, Chungbuk National University School of Medicine. To better understand the trends in the occurrence of cysticercosis and taeniasis in Japan, clinical cases reported in 2005 have been updated. In addition, the current status of Taenia asiatica infections successively occurring in Japan since 2010 is also discussed.     

Evidence of hybridization between Taenia saginata and Taenia asiatica

There has long been a debate as to the specific status of the cestode Taenia asiatica, with some people regarding it as a distinct species and some preferring to recognize it as a strain of Taenia saginata. The balance of current opinion seems to be that T. asiatica is a distinct species. In this study we performed an allelic analysis to explore the possibility of gene exchange between these closely related taxa. In total, 38 taeniid tapeworms were collected from humans living in many localities including Kanchanaburi Province, Thailand where the two species are sympatric. A mitochondrial DNA (mtDNA)-based multiplex PCR tentatively identified those parasites as T. asiatica (n = 20) and T. saginata (n = 18). Phylogenetic analyses of a mitochondrial cytochrome c oxidase subunit 1 (cox1) gene and two nuclear loci, for elongation factor-1 alpha (ef1) and ezrin-radixin-moesin (ERM)-like protein (elp), assigned all except two individual parasites to the species indicated by multiplex PCR. The two exceptional individuals, from Kanchanaburi Province, showed a discrepancy between the mtDNA and nuclear DNA phylogenies. In spite of their possession of sequences typical of the T. saginata cox1 gene, both were homozygous at the elp locus for one of the alleles found in T. asiatica. At the ef1 locus, one individual was homozygous for the allele found at high frequency in T. asiatica while the other was homozygous for the major allele in T. saginata. These findings are evidence of occasional hybridization between the two species, although the possibility of retention of ancestral polymorphism cannot be excluded.     

Interaction and ovicidal activity of nematophagous fungus Pochonia chlamydosporia on Taenia saginata eggs

The ovicidal activity of the nematophagous fungi Pochonia chlamydosporia (isolates VC1 and VC4), Duddingtonia flagrans (isolate AC001) and Monacrosporium thaumasium (isolate NF34) on Taenia saginata eggs was evaluated under laboratory conditions. T. saginata eggs were plated on 2% water-agar with fungal isolates and controls without fungus and examined after 5, 10 and 15 days. At the end of the experiment P. chlamydosporia showed ovicidal activity against T. saginata eggs (p < 0.05), mainly for internal egg colonization with results of 12.8% (VC1) and 2.2% (VC4); 18.1% (VC1) and 7.0% (VC4); 9.76% (VC1) and 8.0% (VC4) at 5, 10 and 15 days, respectively. The other fungi showed only lytic effect without morphological damage to the eggshell. Results demonstrated that P. chlamydosporia was effective in vitro against T. saginata eggs unlike the other fungi.     

Morphologic and genetic identification of Taenia tapeworms in Tanzania and DNA genotyping of Taenia solium

Species identification of Taenia tapeworms was performed using morphologic observations and multiplex PCR and DNA sequencing of the mitochondrial cox1 gene. In 2008 and 2009, a total of 1,057 fecal samples were collected from residents of Kongwa district of Dodoma region, Tanzania, and examined microscopically for helminth eggs and proglottids. Of these, 4 Taenia egg positive cases were identified, and the eggs were subjected to DNA analysis. Several proglottids of Taenia solium were recovered from 1 of the 4 cases. This established that the species were T. solium (n = 1) and T. saginata (n = 3). One further T. solium specimen was found among 128 fecal samples collected from Mbulu district in Arusha, and this had an intact strobila with the scolex. Phylegenetic analysis of the mtDNA cox1 gene sequences of these 5 isolates showed that T. saginata was basal to the T. solium clade. The mitochondrial cox1 gene sequences of 3 of these Tanzanian isolates showed 99% similarity to T. saginata, and the other 2 isolates showed 100% similarity to T. solium. The present study has shown that Taenia tapeworms are endemic in Kongwa district of Tanzania, as well as in a previously identified Mbulu district. Both T. solium isolates were found to have an "African/Latin American" genotype (cox1).     

Molecular Detection of Ancylostoma duodenale,Ancylostoma ceylanicum,and Necator americanus in Humans in Northeastern and Southern Thailand

The 2 principal species of hookworms infecting humans are Necator americanus and Ancylostoma duodenale. Case studies on zoonotic hookworm infections with Ancylostoma ceylanicum and/or Ancylostoma caninum are known mainly from Asian countries. Of these 2 zoonotic species, only A. ceylanicum can develop to adulthood in humans. In the present study, we report a molecular-based survey of human hookworm infections present in southern and northeastern Thailand. Thirty larval hookworm samples were obtained from fecal agar plate cultures of 10 patients in northeastren Thailand and 20 in southern Thailand. Partial ITS1, 5.8S, and ITS2 regions of the ribosomal DNA genes were amplified using PCR. The amplicons were sequenced, aligned, and compared with other hookworm sequences in GenBank database. The results showed that, in Thailand, N. americanus is more prevalent than Ancylostoma spp. and is found in both study areas. Sporadic cases of A. ceylanicum and A. duodenale infection were seen in northeastern Thailand.