Paragonimus heterotremus Chen et Hsia, 1964 (Digenea: Paragonimidae): species identification based on the biological and genetic criteria, and pathology of infection

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. 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. Human paragonimiasis occurs primarily in the tropics and subtropics of Asia, Africa, and the Americas, with different species being responsible in different areas (Table 6.1).

Molecular identification of the trematode P. ichunensis stat. n. from lungs of siberian tigers justified reappraisal of Paragonimus westermani species complex

Flukes from the genus Paragonimus Braun, 1899 are medically important foodborne trematodes predominantly occurring throughout Asian countries. Providing molecular genetic characteristics based on ITS2 and partial 28 S rDNA of the paragonimids from the Russian Far East, Northeast, South, and Southeast Asian countries, we performed a partial reappraisal of Paragonimus westermani species complex. Members of this complex are genetically distinct worms with different divergence times and explosive expansion during Miocene-Pliocene epochs. We confirm the taxonomic status as valid species for P. ichunensis stat. n. (from the Russian Far East and Northern China), and P. filipinus (from the Philippines), which were previously considered subspecies of P. westermani, and reinstated the species name P. pulmonalis (from Japan). We suggest considering the worms from South Korea the Korean variety of P. ichunensis, because Korean specimens are sister and genetically closest to P. ichunensis from Northeast China and Primorsky region of Russia. Worms from South (India (type 2), Sri Lanka), Southeast (Malaysia, Vietnam, Thailand (types 1 and 2)) and East Asia (Taiwan) were left in the paragonimid systematics as Paragonimus sp. We propose to consider Indian worms of type 1 as true P. westermani, but in further revisions, due to the lack of holotype and unknown exact type locality, new type specimens (neotype) should be established.

Lung flukes of the genus Paragonimus: ancient and re-emerging pathogens

The title of this article refers to Table 1 in Zhou (2022, Infectious diseases of poverty: progress achieved during the decade gone and perspectives for the future. Infectious Diseases of Poverty 11, 1), in which it is indicated that Paragonimus species, like many other foodborne trematodes, are ancient pathogens that are also re-emerging to cause disease in modern times. This article provides a general overview of Paragonimus species and the disease they cause. This is followed by comments on several specific topics of current interest: taxonomy and distribution of members of the genus; details of the life cycle; global and regional prevalence of paragonimiasis; genomics of lung flukes and possible effects of global environmental change. Unresolved questions relating to these topics are discussed and gaps in knowledge identified.

Morphological and Molecular Characterization of Paragonimus Species Isolated from Freshwater Crabs in Southern Yunnan, China

Paragonimus species are highly prevalent in various regions of China. The study's objective is to isolate and identify Paragonimus from natural habitats and compare the phylogenetic diversity of Paragonimus in southern Yunnan province, China. Metacercariae of Paragonimus was isolated from crabs, and morphologic identification was performed by microscopy. Metacercariae were injected into experimental Paragonimus free Sprague Dawley rats. After 114 days, adult worms and eggs were isolated from multiple organs. Morphologic identification confirmed the initial identification. DNA was extracted from 5 adult worms, and molecular characterization was performed by amplification and sequencing of CO1 and ITS2 regions, followed by phylogenetic analysis. Out of 447 crabs captured, 186 crabs were found to be infected. A total of 4 species of Paragonimus was observed from naturally infected crabs. Paragonimus microrchis (2), Paragonimus heterotremus (1), Paragonimus proliferus (1), and Paragonimus skrjabini (1) were isolated and identified. A total of 32 sequences were downloaded from the National Center for Biotechnology Information, and 5 sequences generated in the study were used for phylogenetic analysis. In the phylogenetic tree of the CO1 gene, Paragonimus proliferus, Paragonimus heterotremus, and Paragonimus skrjabini were clustered with the same species, and the confidence values of their branches were >95%. A congruent phylogenetic relationship was observed with the ITS2 phylogenetic tree. In the phylogenetic tree constructed with the combined dataset of CO1 and ITS2 datasets, Paragonimus proliferus, Paragonimus heterotremus, and Paragonimus skrjabini clustered with the same species, and their branch confidence values were >94%. Paragonimus microrchis clustered with Paragonimus bangkokensis in both datasets. Phylogenetic analysis revealed robustness of the double loci method as against the single-locus method with either CO1 or ITS2 alone. Paragonimus species isolated from the southern Yunnan province, China, was phylogenetically diverse, and the analysis revealed the clustering of multiple species of Paragonimus isolated from different geographic locations.

Genotoxicity of Paragonimus heterotremus Infection in a Rat Model of Simultaneous Pulmonary and Hepatic Paragonimiasis

Parasites cause numerous health issues in humans, eventually leading to significant social and economic damage; however, the mechanisms of parasite-mediated pathogenesis are not well understood. Nevertheless, it is clearly evidenced that cancerogenic fluke-induced chronic inflammations and cancer are closely associated with oxidative stress. (1) Methods: The Paragonimus heterotremus infection’s genotoxic potential was assessed in a rat model of simultaneous pulmonary and hepatic paragonimiasis by the alkaline version of single-cell gel electrophoresis (comet assay). Statistical analysis of comet parameters was based on the non-parametric Mann–Whitney U test. (2) Results: A clear and statistically significant increase in DNA damage was detected in the helminth-exposed group versus the control rats and the tissue areas adjacent to the parasite capsule versus remote ones; however, differences in DNA damage patterns between different tissues were not statistically significant. Infection resulted in up to 40% cells with DNA damage and an increased genetic damage index. (3) Conclusions: The data obtained contribute to understanding the pathogenesis mechanisms of paragonimiasis, suggesting oxidative stress as the most likely reason for DNA breaks; these findings allow us to consider P. heterotremus as a potentially cancerogenic species, and they are important for the monitoring and treatment of paragonimiasis.

An outbreak of Paragonimus westermani infection among Cambodian technical intern trainees in Japan, exhibiting various extrapulmonary lesions

We encountered an outbreak of paragonimiasis among Cambodian technical intern trainees (TITs) at a food-processing factory in Fukuoka, Japan. The patients were 20-28 years old, seven females and two males, who had been in Japan for one to four years. All of them had consumed raw or undercooked Japanese mitten crab they purchased at a local grocery store near their training place. CT images showed multiple lesions not only in the lungs but in the extrapulmonary organs as well, such as subcutaneous tissues, abdominal muscles, and mesentery, in most of the patients. Their medical records indicated that all of them acquired infection in Japan, not in Cambodia. Diagnosis was made serologically and the patients were treated with praziquantel successfully. Foreign workers and TITs are increasing in Japan so rapidly, that food borne-infections, including paragonimiasis, should be considered in people from developing countries who have exotic dietary habits.