Genetic Variation and Population Genetics of Taenia saginata in North and Northeast Thailand in relation to Taenia asiatica

Genetic Variation of Taenia Saginata Cyst Isolates from Iraq Based on Mitochondrial COX1 Sequences

The zoonotic parasite disease of economic and public health relevance is bovine cysticercosis, resulting from the larval stage of Taenia saginata. The presented research aims to identify intraspecific variation in T. saginata isolated from cattle in Iraq's Sulaymaniyah province using the mitochondrial cytochrome c oxidase subunit 1 (COX1) gene. Sequence analysis of the COX1 gene revealed that five distinct haplotypes were identified in 37 T. saginata specimens from Iraq. Four of the five T. saginata haplotypes may have been identified for the first time in the world. Phylogenetic research revealed that all T. saginata haplotypes had been clustered in a single clade, with Korean and Iranian isolates sharing a high degree of closeness. In addition, individual haplotypes related to COX1 had a pairwise evolutionary divergence of 0.005- 0.013, whereas the overall evolutionary divergence regarding all five haplotypes ranged between 0.000-0.018. It was concluded that added newly recorded data on T. saginata genetic variation could have substantial implications for taeniasis epidemiology and control.

Molecular Identification and Appraisal of the Genetic Variation of Taenia saginata in Central Regions of Vietnam

Taenia saginata is a globally distributed tapeworm responsible for human taeniasis due to the ingestion of raw or undercooked beef. T. saginata is present in several Asian countries, including China, Thailand, Lao PDR, Cambodia, and Vietnam, but little is known about its genetic variation. Studying the tapeworm's phylogeographic patterns is crucial to better understanding their association with the geographic distribution of taeniasis/cysticercosis in human populations. In the present study, 38 specimens of this putative species were collected in central regions of Vietnam and analysed using the mitochondrial gene Cytochrome c Oxidase subunit I (COI) as a molecular marker to assess the correct species identification and investigate the level of genetic variation at different geographic scales. Phylogenetic and phylogeographic analyses were carried out on a dataset that included COI sequences from Vietnamese specimens and from all conspecifics available in GenBank to date. The results showed that the collected Vietnamese specimens belonged to the species T. saginata. In Southeast Asia, signs of a possible founder effect were discovered, with the most common haplotypes frequent and present in many countries, except Lao PDR, which shares its most common haplotype only with individuals from Thailand. Remarkably, a unique taxonomic entity was found worldwide, even though the available COI sequences of T. saginata belonging to non-Asiatic countries are, at present, limited. Therefore, future studies including more COI sequences from a higher number of countries and the use of a combined molecular approach with multiple genetic markers would be useful to provide deeper insight into the global genetic variation of this species.

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).

Taeniasis and cysticercosis in Asia: A review with emphasis on molecular approaches and local lifestyles

Taeniasis is an important parasitic condition in Asia, especially since all three human-infecting Taenia spp., Taenia solium, Taenia saginata, and Taenia asiatica are found in this region. These three species are believed to be sympatrically distributed, with the largest disease burden found in remote and rural areas where people raise pigs and cattle in a traditional manner. Recent studies revealed that T. asiatica and T. saginata are genetically-related sister species that are not completely reproductively isolated from each other. Current evidence indicates that most T. asiatica adult worms are hybrid-derived descendants. Moving forward, nuclear DNA analysis will be critical in further assessing the species circulating locally. Lifestyle choices, such as the consumption of undercooked meat, are important in maintaining the life cycles of these parasites. In addition, poor hygiene and sanitation, in highly endemic areas, make disease control difficult, resulting in the need for sustainable education programs. An overview of the present situation of taeniasis and cysticercosis in Asia is provided, followed by a discussion of molecular approaches to species assessment and the impact of human lifestyles on parasite transmission.

Four Taeniasis saginata Cases Diagnosed at a University Hospital in Korea

In recent years, the taeniasis has been rarely reported in the Republic of Korea (Korea). But in this study, we intend to report 4 taeniasis cases caused by Taenia saginata during a 5-month period (February to June 2018) at a unversity hospital in Gwangju, Korea. Worm samples (proglottids) discharged from all cases were identified by phenotypic and molecular diagnostics. Mitochondrial cytochrome c oxidase subunit I sequences showed 99.4–99.9% identity with T. saginata but, differed by 4% from T. asiatica and by 7% from T. multiceps, respectively. We found that tapeworms in 2 cases (Cases 2 and 3) yielded exactly the same sequences between them, which differed from those in Cases 1 and 4, suggesting intra-species variation in tapeworms. These taeniasis cases by T. saginata infection in this study, which occurred within a limited time period and region, suggest the possibility of a mini-outbreak. This study highlights the need for further epidemiological investigation of potentially overlooked cases of T. saginata infection in Korea.

Genetic Characterization of Taenia saginata Cyst Isolates from Germany

The beef tapeworm Taenia saginata, which causes taeniosis in humans and cysticercosis in cattle, is of medical and economic importance. Understanding the parasite's genetic population structure may help to analyze transmission patterns and aid in the development of control measures. As information on sequence variability is scarce for European isolates, this study aimed to elucidate the intraspecific genetic variability of T. saginata cysts from German cattle by sequence comparison of the mitochondrial cytochrome c oxidase subunit 1 (cox1) and NADH dehydrogenase subunit 5 (nad5) genes, in relationship to sequences from other geographical origins. Cysts were collected from northern German, Swiss, and Belgian cattle. Moreover, proglottids from an adult T. saginata specimen from Palestine were included. Amplification and Sanger sequencing of the cox1 gene was successful for 57 samples (45 German, 9 Swiss, 2 Belgian, 1 Palestinian), whereas 32 sequences were obtained for the nad5 gene (21 German, 10 Swiss, 1 Palestinian). For German isolates, sequence comparison revealed minor genetic variability with two polymorphic sites and mutations in both genes. Three haplotypes with haplotype diversity of 0.088 for cox1 and 0.186 for nad5, as well as nucleotide diversities of 0.00028 and 0.00095, respectively, were observed. Comparison of the cox1 gene sequence of German isolates with other European, African, American, and Asian isolates obtained from National Center for Biotechnology Information (total of 71 sequences) raised 11 polymorphic sites and mutations as well as 10 haplotypes (haplotype diversity: 0.239; nucleotide diversity: 0.00097). Although nad5 sequence comparison comprised less sequences (N = 33), analyses revealed 11 polymorphic sites, 12 mutation sites, and 7 haplotypes (haplotype diversity: 0.335, nucleotide diversity: 0.00391), indicating a better resolution of genetic variability compared to cox1. Thus, nad5 may be particularly useful for in-depth studies on genetic divergence of T. saginata.

Genetic diversity of Taenia saginata (Cestoda: Cyclophyllidea) from Lao People's Democratic Republic and northeastern Thailand based on mitochondrial DNA

BACKGROUND

Taenia saginata is a tapeworm found in cattle worldwide. Analysis of genetic diversity in different geographical populations of T. saginata not only helps to understand the origin, transmission and spread of this organism, but also to evaluate the selection pressures acting on T. saginata and how it is responding to them. However, there are few reports of the genetic variability of T. saginata populations in different regions of the world, including Lao PDR and Thailand. We report the genetic diversity of T. saginata populations in Lao PDR and northeastern Thailand together with sequences of T. saginata from other countries deposited in GenBank.

RESULTS

Mitochondrial cox1 sequence analysis revealed that 15 and 8 haplotypes were identified in 30 and 21 T. saginata isolates from Lao PDR and northeastern Thailand, respectively. Fifty-three haplotypes were identified from 98 sequences. Phylogenetic tree and haplotype network analyses revealed that global isolates of T. saginata were genetically divided into five groups (A, B, C1, C2 and D). Taenia saginata isolates from Lao PDR and northeastern Thailand belonged to either Group A or B. Taenia saginata from western Thailand clustered in groups C1, C2 and D, and populations from the northeast and western Thailand were found to be genetically distinct. Taenia saginata isolates in Lao PDR and Thailand were also found to be genetically diverse but the degree of genetic differentiation was low.

CONCLUSIONS

Taenia saginata populations from Lao PDR and northeastern Thailand are genetically distinct from the population in western Thailand and it is proposed that T. saginata has been dispersed by different transmission routes in Southeast Asia.

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.