The origin of the triploid in Paragonimus westermani on the basis of variable regions in the mitochondrial DNA

General overview of the current status of human foodborne trematodiasis

Foodborne trematodes (FBT) of public health significance include liver flukes (Clonorchis sinensis, Opisthorchis viverrini, O. felineus, Fasciola hepatica and F. gigantica), lung flukes (Paragonimus westermani and several other Paragonimus spp.) and intestinal flukes, which include heterophyids (Metagonimus yokogawai, Heterophyes nocens and Haplorchis taichui), echinostomes (Echinostoma revolutum, Isthmiophora hortensis, Echinochasmus japonicus and Artyfechinostomum malayanum) and miscellaneous species, including Fasciolopsis buski and Gymnophalloides seoi. These trematode infections are distributed worldwide but occur most commonly in Asia. The global burden of FBT diseases has been estimated at about 80 million, however, this seems to be a considerable underestimate. Their life cycle involves a molluscan first intermediate host, and a second intermediate host, including freshwater fish, crustaceans, aquatic vegetables and freshwater or brackish water gastropods and bivalves. The mode of human infection is the consumption of the second intermediate host under raw or improperly cooked conditions. The major pathogenesis of C. sinensis and Opisthorchis spp. infection includes inflammation of the bile duct which leads to cholangitis and cholecystitis, and in a substantial number of patients, serious complications, such as liver cirrhosis and cholangiocarcinoma, may develop. In lung fluke infections, cough, bloody sputum and bronchiectasis are the most common clinical manifestations. However, lung flukes often migrate to extrapulmonary sites, including the brain, spinal cord, skin, subcutaneous tissues and abdominal organs. Intestinal flukes can induce inflammation in the intestinal mucosa, and they may at times undergo extraintestinal migration, in particular, in immunocompromised patients. In order to control FBT infections, eating foods after proper cooking is strongly recommended.

Sporadic endemicity of zoonotic Paragonimus in raccoon dogs and Japanese badgers from Miyazaki Prefecture, Japan

Paragonimiasis is a zoonotic trematode infection caused by Paragonimus spp. To determine the recent status of Paragonimus infections in wild animals, this study investigated Paragonimus spp. in 39 raccoon dogs and 54 Japanese badgers from March 2019 to January 2021 in Miyazaki Prefecture, and examined metacercariae in freshwater crabs. Triploid P. westermani was found in one raccoon dog (2.6%), and metacercariae were recovered from Eriocheir japonica captured near the infected animal collected. One Japanese badger (1.9%) harbored P. skrjabini miyazakii; this prevalence was lower than the approximately 30% that was reported in the 1970s. Results indicated that zoonotic Paragonimus was sporadically prevalent in wild animals. Further investigation in various animals is awaited to elucidate current wildlife reservoirs for those Paragonimus.

Genetic differentiation of Southeast Asian Paragonimus Braun, 1899 (Digenea: Paragonimidae) and genetic variation in the Paragonimus heterotremus complex examined by nuclear DNA sequences

Southeast Asian lung flukes, the causative agents of human and animal paragonimiasis, comprise at least 14 species. Of these, seven species; Paragonimus bangkokensis, P. harinasutai, P. macrorchis, P. siamensis, P. westermani, P. heterotremus and P. pseudoheterotremus were studied. Two regions of domain 1 of taurocyamine kinase; TkD1 (exon) and TkD1Int2 (intron 2), were used as genetic markers for elucidating their genetic differentiation, genetic variation, and heterozygosity. The TkD1 region was conserved between these species but can potentially be used to differentiate all seven species. However, the TkD1Int2 region had a high level of polymorphism, which is suitable for investigation of genetic variation within or between closely related species, especially P. heterotremus and P. pseudoheterotremus as well as for a phylogenetic analyses of the genus Paragonimus. Heterozygosity was mostly observed in DNA samples extracted from adult P. heterotremus including samples taken from sputum of paragonimiasis patients, whereas DNA extracted from metacercariae was not, except in the samples from Myanmar. Our findings provide evidence of DNA recombination and incomplete lineage sorting of P. heterotremus and P. pseudoheterotremus in TkD1Int2, which suggesting gene flow between these two species.

Paragonimiasis

Paragonimiasis is a zoonotic disease caused by lung flukes of the genus Paragonimus. Humans usually become infected by eating freshwater crabs or crayfish containing encysted metacercariae of these worms. However, an alternative route of infection exists: ingestion of raw meat from a mammalian paratenic host. Adult worms normally occur in pairs in cysts in the lungs from which they void their eggs via air passages. The pulmonary form is typical in cases of human infection due to P. westermani, P. heterotremus, and a few other species (Table 5.1). Worms may occupy other sites in the body, notably the brain, but lung flukes have made their presence felt in almost every organ. Ectopic paragonimiasis is particularly common when infection is due to members of the P. skrjabini complex (Table 5.1). Human paragonimiasis occurs primarily in the tropics and subtropics of Asia, Africa, and the Americas, with different species being responsible in different areas (Table 5.1).

Molecular and morphological variation of Paragonimus westermani in Vietnam with records of new second intermediate crab hosts and a new locality in a northern province

Paragonimus westermani is one of the most medically important lung flukes and is widely distributed in Asia. It exhibits considerable variation in morphological, genetic and biological features. In central provinces of Vietnam, a high prevalence of metacercariae of this species has been reported from the crab intermediate host, Vietopotamon aluoiense. In this study, we detected P. westermani metacercariae in two additional crab hosts, Donopotamon haii in Quang Tri Province, central Vietnam and Indochinamon tannanti in Yen Bai Province in the north. The latter is a new locality for P. westermani in a northern region of Vietnam where P. heterotremus is the only species currently known to cause human paragonimiasis. Paragonimus westermani metacercariae found in Vietnam showed considerable morphological variation but slight genetic variation based on DNA sequences from the nuclear ribosomal ITS2 region and the mitochondrial 16S gene. Co-infection of the same individual crabs with P. westermani and P. heterotremus and/or some other Paragonimus species was found frequently, suggesting potential for co-infection in humans. The findings of the present study emphasize the need for highly specific molecular and immunodiagnostic methods to differentially diagnose between P. westermani and P. heterotremus infections.

Paragonimiasis

Paragonimiasis is a zoonotic disease caused by lung flukes of the genus Paragonimus. Humans usually become infected by eating freshwater crabs or crayfish containing encysted metacercariae of these worms. However, an alternative route of infection exists: ingestion of raw meat from a mammalian paratenic host. Adult worms normally occur in pairs in cysts in the lungs from which they void their eggs via air passages. The pulmonary form is typical in cases of human infection due to P. westermani, P. heterotremus, and a few other species (Table 5.1). Worms may occupy other sites in the body, notably the brain, but lung flukes have made their presence felt in almost every organ. Ectopic paragonimiasis is particularly common when infection is due to members of the P. skrjabini complex (Table 5.1). Human paragonimiasis occurs primarily in the tropics and subtropics of Asia, Africa, and the Americas, with different species being responsible in different areas (Table 5.1).

Sequence variability in two mitochondrial DNA regions and internal transcribed spacer among three cestodes infecting animals and humans from China

Sequence variability in two mitochondrial DNA (mtDNA) regions, namely cytochromecoxidase subunit 1 (cox1) and NADH dehydrogenase subunit 4 (nad4), and internal transcribed spacer (ITS) of rDNA among and within three cestodes,Spirometra erinaceieuropaei,Taenia multicepsandTaenia hydatigena, from different geographical origins in China was examined. A portion of thecox1 (pcox1),nad4 genes (pnad4) and the ITS (ITS1+5.8S rDNA+ITS2) were amplified separately from individual cestodes by polymerase chain reaction (PCR). Representative amplicons were subjected to sequencing in order to estimate sequence variability. While the intra-specific sequence variations within each of the tapeworm species were 0–0.7% for pcox1, 0–1.7% for pnad4 and 0.1–3.6% for ITS, the inter-specific sequence differences were significantly higher, being 12.1–17.6%, 18.7–26.2% and 31–75.5% for pcox1, pnad4 and ITS, respectively. Phylogenetic analyses based on the pcox1 sequence data revealed thatT. multicepsandT. hydatigenawere more closely related to the other members of theTaeniagenus, andS. erinaceieuropaeiwas more closely related to the other members of theSpirometragenus. These findings demonstrated clearly the usefulness of mtDNA and rDNA sequences for population genetic studies of these cestodes of socio-economic importance.

An infectious topic in reticulate evolution: introgression and hybridization in animal parasites

Little attention has been given to the role that introgression and hybridization have played in the evolution of parasites. Most studies are host-centric and ask if the hybrid of a free-living species is more or less susceptible to parasite infection. Here we focus on what is known about how introgression and hybridization have influenced the evolution of protozoan and helminth parasites of animals. There are reports of genome or gene introgression from distantly related taxa into apicomplexans and filarial nematodes. Most common are genetic based reports of potential hybridization among congeneric taxa, but in several cases, more work is needed to definitively conclude current hybridization. In the medically important Trypanosoma it is clear that some clonal lineages are the product of past hybridization events. Similarly, strong evidence exists for current hybridization in human helminths such as Schistosoma and Ascaris. There remain topics that warrant further examination such as the potential hybrid origin of polyploid platyhelminths. Furthermore, little work has investigated the phenotype or fitness, and even less the epidemiological significance of hybrid parasites.

Paragonimus westermani and Some Rare Intestinal Trematodes Recovered from Raccoon Dogs (Nyctereutes procyonoides viverrinus) Introduced Recently on Yakushima Island, Japan

Helminth parasites were collected from 9 raccoon dogs (Nyctereutes procyonoides viverrinus) and 2 Japanese weasels (Mustela itatsi sho) on Yakushima Island, Japan. The former carnivore was introduced to this World Natural Heritage Area presumably within the last two decades, expanding its population thence, although detailed process(es) of the introduction is unknown. The collected trematodes from raccoon dogs included the triploid form of Paragonimus westermani, Brachylaima tokudai, Maritrema eroliae, and Pseudocryptotropa sp. Simultaneously, Paragonimus ohirai was found in one weasel killed by a traffic accident. Although the triploid form of P. westermani and P. ohirai are known to be distributed in some river-mouth areas of Yakushima Island based on previous surveys on crab hosts, natural infection was detected for the first time in wild final hosts. Particularly, the raccoon dog infected with P. westermani was caught in a mountainous area, distant from human residence or river-mouth areas. Although it is possible that the infected raccoon dog moved from a river-mouth area endemic with P. westermani after infection, the alternative scenario remains to be pursued; the endemic area of this zoonosis is expanding along with the recent expansion of raccoon dogs or feral cats (Felis catus), that became prevalent recently on this island including the mountainous areas. Maritrema eroliae taking a variety of shorebirds as its natural final hosts, and a minute trematode, Pseudocryptotropa sp., taking unknown natural final host(s) were recorded for the first time in raccoon dogs.

Advances and Trends in the Molecular Systematics of the Parasitic Platyhelminthes

The application of molecular systematics to the parasitic Platyhelminthes (Cestoda, Digenea and Monogenea) over the last decade has advanced our understanding of their interrelationships and evolution substantially. Here we review the current state of play and the early works that led to the molecular-based hypotheses that now predominate in the field; advances in their systematics, taxonomy, classification and phylogeny, as well as trends in species circumscription, molecular targets and analytical methods are discussed for each of the three major parasitic groups. A by-product of this effort has been an ever increasing number of parasitic flatworms characterized genetically, and the useful application of these data to the diagnosis of animal and human pathogens, and to the elucidation of life histories are presented. The final section considers future directions in the field, including taxon sampling, molecular targets of choice, and the current and future utility of mitochondrial and nuclear genomics in systematic study.