Inactivation of Paragonimus westermani metacercariae in soy sauce-marinated and frozen freshwater crabs.

Soy sauce-marinated freshwater crabs (Eriocheir japonicus) are a source of human paragonimiasis. The viability of Paragonimus westermani metacercariae (PwMc) in marinated crabs was investigated in an experimental setting. The PwMc collected from freshwater crayfish were inoculated into freshwater crabs, which were then frozen or marinated in soy sauce. All PwMc in the freshwater crabs were inactivated after freezing for 48 h at -20 °C and after freezing for 12 h at -40 °C. After marinating for 32 days, the survival rate of PwMc in 5% NaCl soy sauce was 50%, in 7.5% NaCl soy sauce it was 33.3%, and in 10.0% NaCl soy sauce it was 31.3%. When marinated for 64 days, all PwMc were inactivated in all experimental groups. These results revealed that freezing and soy sauce marination were detrimental to the survival of PwMc in freshwater crabs. Specifically, freezing crabs for more than 48 h or soaking them in soy sauce containing at least 5.0% NaCl for 64 days can inactivate PwMc. These results can inform the production of the traditional Korean soy sauce-marinated freshwater crabs known as gejang.

Presence of three distinct genotypes within the Paragonimus westermani complex in northeastern India.

The name Paragonimus westermani (Kerbert, 1878) is commonly applied to members of a species complex that includes the well-known Asian lung fluke of medical and veterinary importance. Unambiguous molecular and morphological evidence showing the presence of a member of the complex in India has recently been published. In the present study we report the occurrence of 2 more members of the P. westermani complex in northeastern (NE) India. Surveys of the freshwater crabs Maydelliatelphusa lugubris in NE India revealed 2 morphologically distinct types of lung fluke metacercariae. Phylogenetic analyses, using DNA sequences from ITS2, 28S and cox1 gene regions indicate that these lung metacercariae belong to P. westermani complex. Type 1 metacercariae have a more basal position within the complex whereas type 2 metacercariae are closely related to the relatively derived forms of P. westermani from NE Asia (Japan, Korea, China) and Vietnam. A third type of metacercaria (type 3), detected in another crab host, Sartoriana spinigera in Assam, was phylogenetically close to P. siamensis, also a member of the P. westermani group. Molecular evidence has demonstrated the existence of 3 genotypes of lung flukes within the Paragonimus westermani complex in NE India. Two of these were previously unknown.

Paragonimus westermani possesses aerobic and anaerobic mitochondria in different tissues, adapting to fluctuating oxygen tension in microaerobic habitats.

We previously showed that adult Paragonimus westermani, the causative agent of paragonimiasis and whose habitat is the host lung, possesses both aerobic and anaerobic respiratory chains, i.e., cyanide-sensitive succinate oxidase and NADH-fumarate reductase systems, in isolated mitochondria (Takamiya et al., 1994). This finding raises the intriguing question as to whether adult Paragonimus worms possess two different populations of mitochondria, one having an aerobic succinate oxidase system and the other an anaerobic fumarate reductase system, or whether the worms possess a single population of mitochondria possessing both respiratory chains (i.e., mixed-functional mitochondria). Staining of trematode tissues for cytochrome c oxidase activity showed three types of mitochondrial populations: small, strongly stained mitochondria with many cristae, localised in the tegument and tegumental cells; and two larger parenchymal cell mitochondria, one with developed cristae and the other with few cristae. The tegumental and parenchymal mitochondria could be separated by isopycnic density-gradient centrifugation and showed different morphological characteristics and respiratory activities, with low-density tegumental mitochondria having cytochrome c oxidase activity and high-density parenchymal mitochondria having fumarate reductase activity. These results indicate that Paragonimus worms possess three different populations of mitochondria, which are distributed throughout trematode tissues and function facultatively, rather than having mixed-functional mitochondria.

Hepatic paragonimiasis revealed by FDG PET/CT.

A 72-year-old asymptomatic man with a hepatic lesion incidentally detected by ultrasonography in routine examination undertook fluorodeoxyglucose (FDG)-positron emission tomography/computed tomography for further evaluation. The images revealed increased FDG activity in the lesion, which was suggestive of malignancy. However, the pathologic examination demonstrated that the lesion was a granuloma caused by Paragonimus westermani, a lung fluke. Although increased FDG activity in the lung due to P. westermani infection is expected and reported previously, such lesion identified in the liver by FDG positron emission tomography/computed tomography is unusual.

Two novel phospholipid hydroperoxide glutathione peroxidase genes of Paragonimus westermani induced by oxidative stress.

SUMMARY: Phospholipid hydroperoxide glutathione peroxidase (PHGPx; GPx4) plays unique roles in the protection of cells against oxidative stress by catalysing reduction of lipid hydroperoxides. We characterized 2 novel GPx genes from a lung fluke, Paragonimus westermani (designated PwGPx1 and PwGPx2). These single copy genes spanned 6559 and 12 371 bp, respectively, and contained each of 5 intervening introns. The PwGPx2 harboured a codon for Sec and a Sec insertion sequence motif. Proteins encoded by the Paragonimus genes demonstrated a primary structure characteristic to the PHGPx family, including preservation of catalytic and glutathione-binding domains and absence of the subunit interaction domain. Expression of PwGPx1 increased gradually as the parasite matured, whereas that of PwGPx2 was temporally regulated. PwGPx2 was expressed at the basal level from the metacercariae to the 3-week-old juveniles; however, the expression was significantly induced in the 7-week-old immature worms and reached a plateau in the 12-week-old adults and eggs. PwGPx1 and PwGPx2 were largely localized in vitellocytes within vitelline glands and eggs. Oxidative stress-inducible paraquat, juglone and H2O2 substantially augmented the PwGPx1 and PwGPx2 expressions in viable worms by 1.5- to 11-fold. Our results strongly suggested that PwGPxs may actively participate in detoxification of oxidative hazards in P. westermani.

Paragonimus westermani: biochemical and immunological characterizations of paramyosin.

Paramyosin of the helminth parasite is a muscle protein that plays multifunctional roles in host-parasite relationships. In this study, we have cloned a gene encoding Paragonimus westermani paramyosin (PwPmy) and characterized biochemical and immunological properties of the recombinant protein. The recombinant PwPmy (rPwPmy) was shown to bind both human immunoglobulin G (IgG) and collagen. The protein was constitutively expressed in various developmental stages of the parasite and its expression level increased progressively as the parasite matured. Immunohistological analysis revealed that PwPmy was mainly localized in subtegumental muscle, tegument and cells surrounding the oral sucker, intestine, and ovary of the parasite. Sera from patients with paragonimiasis showed antibody reactivity against rPwPmy, and IgG1 and IgG4 were predominant. Immunization of mice with rPwPmy also induced high IgG responses. Biochemical and immunological characterization of PwPmy may provide valuable information for the further study to develop a vaccine or a chemotherapeutic agent for paragonimiasis.

Differential expression of Paragonimus westermani eggshell proteins during the developmental stages.

Eggs of trematode parasites are comprised of numerous vitelline cells and one fertilized ovum, and are encapsulated within a protein shell provided by the vitellocytes. In this study, we isolated two full-length cDNA clones that showed substantial levels of sequence identity with trematode-specific eggshell precursor proteins from the human lung fluke, Paragonimus westermani. These cDNAs, designated Pw-Vit20 (868-bp-long) and Pw-Vit36 (883-bp-long), shared a 76% identity with one another at the nucleotide level, and each encoded a 261-amino acid (aa) polypeptide. The deduced aa sequences contained a N-terminal hydrophobic segment, as well as a sequence motif of Gly-Gly-Gly-Tyr-Asp-Asn/Thr-Tyr-Gly-Lys/Gln, which is highly homologous with the eggshell proteins of Fasciola hepatica. With the high frequencies of tyrosine, glycine and lysine, the positions occupied by tyrosine, which has been proved to be converted into dihydroxyphenylalanine, were well preserved. Pw-Vit20 and Pw-Vit36 were found to be monoexonic genes with variably diverged variants scattered into multiple genomic loci. Their protein products were localized in the vitelline follicles and eggshells. Expression of Pw-Vit20 was restricted to the egg and adult stages, thus suggesting a critical involvement of Pw-Vit20 in the parasite's fecundity activity. Conversely, Pw-Vit36 was constitutively expressed in the metacercariae and juvenile stages in the vitelline follicles and ducts, which suggested that the prepositioning of stem or primordial vitelline cells within the juveniles prior to sexual maturation. Pw-Vit36 might acquire a unique or additional function relevant to the maturation and/or development of the vitelline cells/follicles during the evolutionary period of P. westermani. Differential biological implications of multiple eggshell precursor proteins may provide insight into the molecular mechanism of eggshell formation and the developmental process of the vitelline follicles in the parasitic trematode.

Early cysteine protease activity in excretory bladder triggers metacercaria excystment of Paragonimus westermani.

The cysteine proteases of Paragonimus westermani metacercaria are known to initiate metacercaria excystment. However, their secretory sites, such as the intestine, tegument, and excretory bladder are not well defined. In this study, the metacercariae were labeled with bromodeoxyuridine (BrdU) to distinguish the initial activation sites. BrdU was labeled mainly at the excretory bladder and the excretory granules of the metacercariae and the newly excysted juvenile worms. This result shows that early 'defecation' of the proteases from the excretory bladder may accelerate the excystment of P. westermani metacercariae.