Recent Incidence of Paragonimus westermani Metacercariae in Freshwater Crayfish, Cambaroides similis, from Two Enzootic Sites in Jeollanam-do, Korea

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).

What Findings on Chest CTs Can Delay Diagnosis of Pleuropulmonary Paragonimiasis?

Purpose: The purpose of this study was to investigate which findings were delayed in diagnosis with respect to chest CT findings of paragonimiasis. Methods: This retrospective, informed questionnaire study was conducted to evaluate chest CT scans of 103 patients (58 men and 45 women; mean age 46.1 ± 14.6 years). The patients were diagnosed with paragonimiasis from 2003 to 2008 in four tertiary hospitals. Statistical analysis was performed using the chi-square test to identify differences between an initially correct diagnosis and an incorrect one of paragonimiasis on chest CT scans, for which we evaluated such variables as the location of lesion, type of parenchymal lesions, and worm migration track. Results: Nodular opacities on chest CT scans were the most common findings (53/94, 56.4%). The sign of worm migration tracks was only present in 18.1% of cases (17/94). Although statistically insignificant, the form of consolidation (18/25, 72%) and mass (6/8, 75%) on CT was common in correct diagnostics, and the form of the worm migration track (12/17, 70.6%) was high in correct diagnostics. Conclusion: A delayed diagnosis of paragonimiasis may often be made in patients with non-nodular, parenchymal lesions who are negative for worm migration track on chest CT scans.

Morphological and Molecular Characterization of Paragonimus skrjabini Complex from Yunnan, China: A Brief Report

Purpose

To perform environmental sampling and molecular identification of Paragonimus in endemic regions, which may help in minimizing transmission among humans.

Methods

Mountain crabs from the genus Potamiscus were collected and the encysted metacercariae were extracted and subjected to morphological identification, followed by animal inoculation in Sprague–Dawley (SD) rats. After 112 days of infection, animals were killed and adult worms were extracted from lungs and muscles. The morphology of adult worms was characterized by microscopy and molecular identification was done by polymerase chain reaction, followed by sequencing of cox1 and ITS2 genes. Phylogenetic analysis was done by maximum parsimony method.

Results

A total of 447 crabs were captured from the streams of Tongchang Town, Jinping County, Yunnan Province, China. The infection rate was found to be 41% (186 out of 447 crabs). The metacercariae of Paragonimus skrjabini was identified by the characteristics round or spherical encysted form measuring 410 to 460 × 400 to 460 µm. After animal infection in SD rats, adults were presumptively confirmed to be P. skrjabini, which was also confirmed by gene amplification and sequence analysis of cox1 and ITS2 regions. Paragonimus skrjabini clustered with previously reported P. skrjabini from Yunnan and Vietnam. The confidence values of their branches were > 95%. Phylogenetic analysis of the ITS2 region revealed two distinct clusters with distinct geographical grouping. Phylogenetic analysis with the combined data sets reiterated the geographical grouping with P. skrjabini from Yunnan clustering with strains from Vietnam.

Conclusion

Metacercariae of P. skrjabini was discovered in freshwater crabs in Yunnan province, China, and the strains were phylogenetically related to P. skrjabini from Vietnam.

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.

Paragonimus and its hosts in China: An update

Paragonimiasis is an important foodborne parasitic disease. Over 50 species of Paragonimus have been reported worldwide, and China has the widest distribution and largest number of species. The detection of Paragonimus metacercariae from second intermediate hosts has been reported in 22 provinces and municipalities. The most frequently reported species are P. westermani, P. skrjabini, P. heterotremus and Euparagonimus cenocopiosus. In this review, we collected and reviewed relevant reports on the detection of Paragonimus metacercariae in second intermediate hosts from 1937 to 2020 from all areas of China. We provide an updated and current summary of Paragonimus species and their hosts in China. Data on the geographical range, species distribution, and second intermediate host species of Paragonimus were extracted. ArcGIS10.2 software was used to generate distribution maps of Paragonimus for four time periods: 1937-1990, 1991-2005, 2006-2020 and 1937-2020. We analyzed the geographic and spatiotemporal dynamics of Paragonimus prevalence in natural foci and provided a basis for further research and paragonimiasis prevention strategies in China.

Paragonimus and paragonimiasis in Asia: An update

Paragonimiasis, or lung fluke disease, is a typical food-borne parasitic zoonosis caused by infection with trematodes belonging to the genus Paragonimus. More than 50 species of Paragonimus have been reported throughout the world, of which seven valid species infect humans, an estimated one million people annually worldwide. Among the seven species, P. westermani, P. heterotremus, and P. skrjabini/P. s. miyazakii, distributed in Asia, are the most important species as the cause of paragonimiasis. Humans acquire infection through the ingestion of raw, pickled or undercooked freshwater crustaceans, 2nd intermediate hosts, or consuming raw meat of wild boar or deer, paratenic hosts. Infections often occur clustered in foci where dietary habits allow transmission of the parasites. Paragonimiasis typically causes a subacute to chronic inflammatory disease of the lungs. The symptoms, including chronic cough, chest pain, dyspnea and hemoptysis, mimic those of tuberculosis and lung cancer. Serologic tests are commonly used for the diagnosis of paragonimiasis, and Praziquantel is the treatment of choice. In this review, the current status of Paragonimus and paragonimiasis in Asia is outlined based on the latest information and findings. We also summarize current trends of paragonimiasis in Japan, which is one of the most endemic area of paragonimiasis in the world, for the better understanding and control of paragonimiasis.

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).