Susceptibility of inbred mice to Paragonimus miyazakii infection

Differences in the susceptibility among inbred strains of mice to Paragonimus miyazakii infection were examined. Recovery of worms varied among the strains used. More were recovered from BALB/c mice than from any of the other strains; whereas, the fewest were recovered from C57BL/6 and C57BL/10. No worm formed a cyst in the lung or matured in any of the strains.     

Co-existence of Paragonimus harinasutai and Paragonimus bangkokensis metacercariae in fresh water crab hosts in central Viet Nam with special emphasis on their close phylogenetic relationship

During our epidemiological surveys for Paragonimus species in central Viet Nam, we found four morphologically different Paragonimus metacercariae in mountainous crabs. They were identified as metacercariae of Paragonimus westermani, P. bangkokensis, P. proliferus, and P. harinasutai in the order of their prevalence in crab hosts. This is the first discovery of P. harinasutai in Viet Nam, co-inhabiting with P. bangkokensis and other species. Metacercariae of P. harinasutai were given orally to a cat to obtain adult worms. Then, ITS2 and CO1 sequences of metacercariae and adults of P. harinasutai, and metacercariae of P. bangkokensis collected from the same place were determined for analyses of phylogenetic relationships to other P. harinasutai and P. bangkokensis populations as well as related species. The results of molecular analyses showed that P. harinasutai from Quang Binh province of central Viet Nam was almost completely identical with those from Vientiane, Lao PDR; P. bangkokensis from Quang Binh, Viet Nam was also almost completely identical with those from Lao PDR and from Quang Ninh province, Viet Nam. Except for one P. harinasutai isolate from China, all populations of P. harinasutai and P. bangkokensis from Thailand, Lao and Viet Nam make a single clade in both ITS2 and CO1 trees. In ITS2 sequences, AT deletion and ATC insertion were observed in some isolates of both species, indicating recent gene flow between P. harinasutai and P. bangkokensis. Moreover, because of their extremely high genetic similarities and their co-inhabitation in the same crab hosts found in Thailand, Lao PDR and Viet Nam, they should be considered as the sister species at the early stage of divergence. In addition, P. microrchis previously described from Yunnan, China should be placed as the synonym of P. harinasutai, because of their morphological and molecular similarities.     

Electron microscopic study of spermatogenesis in the lung fluke (Paragonimus miyazakii)

Summary The characteristics of spermatogenesis in a type of pulmonary parasite, Paragonimus miyazakii have been observed using the electron microscope. Groups of several spermatocytes revealed mutual cytoplasmic connection. That degree of this fusion increased as spermatogenesis progressed, and finally developed into a so-called cytophore. Then, this cytophore remained joined with a spermatid by a short stalk until the spermatid changed into a sperm. The nucleus of the spermatid became elongated with a string-like arrangement of the chromatin, which, in turn, showed increased electron density. At the pole of the spermatid, linearly arranged microtubules developed just below the plasma membrane. Close to an elongated portion at the pole, two separate flagella start growing and later fuse with the sperm itself. In the sperm tail a couple of tail filament complexes, longitudinally oriented slender mitochondria, and a tubular structure were present.     

Infection dynamics of Centrocestus armatus cercariae (Digenea: Heterophyidae) to second intermediate fish hosts

The infection dynamics of Centrocestus armatus cercariae with respect to second intermediate fish hosts were investigated using cercariae collected from naturally infected Semisulcospira libertina. Cercariae survival and infectivity were recorded at 2-hr intervals. Survival remained constant but decreased abruptly at 30 hr of age. An age-dependent model presented the best-fit curve for the survival data (r2 0.936), implying that cercariae tended to allocate resources equally among themselves and then died once those resources were depleted. Cercariae infectivity remained constant over the first 10 hr of life and then declined; an age-dependent model also provided a better fit (r2 = 0.956). The transmission rate of C. armatus cercariae to the fish host was relatively low near the time of emergence from the snail host but peaked at 85% after 1 hr and then maintained a plateau period until 5 hr of exposure to fish. The pattern of transmission was also investigated initially at varying densities of cercariae and then by maintaining a constant cercariae density but varying the total number. Results revealed that the pattern of transmission was frequency-dependent.     

Attachment and penetration of Centrocestus armatus (Digenea: Heterophyidae) cercariae to gills of secondary intermediate fish hosts

The attachment and penetration of Centrocestus armatus cercariae into the fish host Zacco temmincki are described in this study. Light and scanning electron microscopy (SEM) were used to examine the topographical features and behavior of cercariae. Histochemistry and transmission electron microscopy (TEM) were employed to trace glandular products and secretions released by cercariae during penetration. Cercariae are first carried into the fish gill chambers via the respiratory currents. The frequency of respiratory-current reversals of fish increased when infected with cercariae. The behavior of cercariae, during breaks in current flow that preceded each current reversal, was observed using a specially devised apparatus. Cercariae produce a mucus-like secretion upon attachment, shed their tail, and employ a brief period of leech-like creeping behavior before penetration. In all cases, the site of penetration was via the surface of the primary gill lamellae. SEM revealed a well-developed anterior penetration apparatus, and a highly contractile body region, that created a driving force for penetration. TEM and histochemistry showed that the mucus observed on the surface tegument of cercariae during attachment were glandular secretions from the parasite. The significance of fish respiratory current reversals to the success of cercariae penetration nicely illustrates the exploitation by the parasite of a host response to a stimulus.     

Studies on the in vitro effects of bithionol and menichlopholan on flukes of Clonorchis sinensis, Metagonimus takahashii and Paragonimus miyazakii.

The present study was carried out in order to obtain information on the action of bithionol and menichlopholan on Clonorchis sinensis, Metagonimus takahashii and Paragonimus miyazakii. The drugs inhibited the motility of the newly excysted juveniles and adult worms in vitro. Moreover, the in vitro treatment slightly decreased lactate dehydrogenase activity in homogenates of adult worms. The drug treatments of adult worms in vitro also inhibited the activity of fumarate reductase, malic enzyme, phosphogluconate dehydrogenase and succinate dehydrogenase in the homogenate. In addition to this, these drugs caused morphological alterations in the ultrastructure of the tegument of the flukes.     

The infestation and dispersion patterns of Carcinonemertes spp. (Nemertea) on their crab hosts

Seasonal changes in the infestation and dispersion patterns of egg predatory nemerteans on their crab hosts were analyzed. Marked differences in the seasonal patterns of infestation were noted between worm species, yet, common patterns in the aggregation of the worms were found. Worm aggregation increased at the onset of the reproductive seasons of the hosts, and at the nadirs of the reproductive seasons for those hosts with year round breeding. The aggregation patterns of two worm species fluctuated with the physical environment of their estuarine hosts. Salinity changes as a result of seasonal rains may have caused changes in the underlying dispersion patterns of Carcinonemertes epialti on Hemiarapsus oregonensis, and C. mitsukurii on Portunus pelagicus. Lastly, the embryogenic cycle of the host species was significant in shaping the infestation and aggregation patterns of C. epialti on Cancer anthonyi and C. regicides on Paralithodes camtschaticus. Worm immigration and emigration were linked to crab embryogenesis and directly influenced the dispersion patterns of the worms.     

Infection of mammalian hosts by milk-borne nematode larvae: A review

Milk-borne or transmammary infection has been observed to occur in several host-parasite systems. In the order of their observation, these are Uncinaria lucasi-fur seal; Strongyloides ransomi-swine; Ancylostoma caninum-dog; Toxocara canis-dog; Strongyloides westeri-horse; Neoascaris vitulorum-cow; Strongyloides papillosus-cow and -sheep; and Toxocara cati-cst. Some of these parasites are largely dependent on milk-borne infection of neonatal animals. All have a tissue migratory phase in their life cycle. Most of these parasites also utilize other modes or combinations of modes in infecting new hosts. The potential importance of milk-borne infection as a factor in human hookworm disease is pointed out as is the need for complete assessment of this avenue of infection.     

Codivergence of mycoviruses with their hosts

Background

The associations between pathogens and their hosts are complex and can result from any combination of evolutionary events such as codivergence, switching, and duplication of the pathogen. Mycoviruses are RNA viruses which infect fungi and for which natural vectors are so far unknown. Thus, lateral transfer might be improbable and codivergence their dominant mode of evolution. Accordingly, mycoviruses are a suitable target for statistical tests of virus-host codivergence, but inference of mycovirus phylogenies might be difficult because of low sequence similarity even within families.

Methodology

We analyzed here the evolutionary dynamics of all mycovirus families by comparing virus and host phylogenies. Additionally, we assessed the sensitivity of the co-phylogenetic tests to the settings for inferring virus trees from their genome sequences and approximate, taxonomy-based host trees.

Conclusions

While sequence alignment filtering modes affected branch support, the overall results of the co-phylogenetic tests were significantly influenced only by the number of viruses sampled per family. The trees of the two largest families, Partitiviridae and Totiviridae, were significantly more similar to those of their hosts than expected by chance, and most individual host-virus links had a significant positive impact on the global fit, indicating that codivergence is the dominant mode of virus diversification. However, in this regard mycoviruses did not differ from closely related viruses sampled from non-fungus hosts. The remaining virus families were either dominated by other evolutionary modes or lacked an apparent overall pattern. As this negative result might be caused by insufficient taxon sampling, the most parsimonious hypothesis still is that host-parasite evolution is basically the same in all mycovirus families. This is the first study of mycovirus-host codivergence, and the results shed light not only on how mycovirus biology affects their co-phylogenetic relationships, but also on their presumable host range itself.     

Attachments by parasitic lampreys within the branchial cavities of their hosts

Silver Lamprey (Ichthyomyzon unicuspis) in the Wisconsin River attached within the branchial cavity of Paddlefish (Polyodon spathula) significantly more often (6.5% of 1,578 attachments) than would be expected by chance on the basis of its relative surface area (3.7%), with as many as four lampreys found together within the branchial cavity of the same Paddlefish. Similar behavior has occasionally been noted for lampreys in other systems, but the phenomenon may be underreported when the lampreys are concealed from view. As suggested previously for some parasitic trychomycterid catfishes, lampreys in the branchial cavity may benefit from accessing blood under pressure, especially in the ventral aorta. In addition, Silver Lamprey within the branchial cavities of Paddlefish may be relatively protected from any negative effects that might result from Paddlefish breaching.