Chaetotaxy and ultrastructure of sensory receptors in the cercaria of a species of Allassogonoporus Olivier, 1938 (Digenea:Lecithodendriidae)

A standard procedure that combines chaetotaxic, ultrastructural and neuromorphological observations has recently provided a new perspective to the study of cercarial sensory systems. In the present work, we aimed to extend the use of this combination of techniques to investigate the chaetotaxy of Allassogonoporus sp. in conjunction with the ultrastructure of sensory receptors and neuromorphology. Five nerve regions were distinguished. A conspicuous bilobed cerebral ganglion was observed at the level of the pharynx. The chaetotaxic pattern was generally consistent with that of other lecithodendriids. Four types of receptors were distinguished with scanning electron microscopy. These types differed in cilium length (short, moderately long or long) and tegumentary collar length (moderately low or high). Internal ultrastructure of receptor type IIAL revealed an unsheathed cilium, a closed basal body, septate extracellular junctional complexes and thickened nerve collars. Some receptor types were site-specific. Long uniciliated receptors were found mainly on the dorsal surface, whereas short uniciliated receptors were widespread across the tegument. Ultrastructure and site-specificity observations suggest that most sensory receptors are mechanoreceptors, probably reflecting the important role mechanoreception plays in host finding.     

Neorickettsia risticii is vertically transmitted in the trematode Acanthatrium oregonense and horizontally transmitted to bats

Potomac horse fever is known to be transmitted through the ingestion of caddisflies parasitized with Neorickettsia (formerly Ehrlichia) risticii-infected metacercaria. However, the species of trematode involved and how N. risticii is maintained in nature are unknown. In this study, gravid trematodes were recovered from the intestines of 12 out of 15 Eptesicus fuscus big brown bats and eight out of nine Myotis lucifugus little brown bats from various sites in Pennsylvania, USA. Trematode specimens isolated from six E. fuscus bats contained N. risticii DNA. The trematode was identified as Acanthatrium oregonense. N. risticii was detected within individual trematode eggs by polymerase chain reaction as well as by immunofluorescence labelling with an anti-N. risticii antibody, indicating that N. risticii is vertically transmitted (from adult to egg) in A. oregonense. Furthermore, N. risticii DNA was detected in the blood, liver or spleen of 23 out of 53 E. fuscus and M. lucifugus bats, suggesting that N. risticii can also be transmitted horizontally from trematode to bat. These results indicate that A. oregonense is a natural reservoir and probably a vector of N. risticii.     

Growth and development of Pleurogenoides orientalis (Srivastava, 1934) (Trematoda: Lecithodendriidae) in the intermediate and definitive hosts

Two phases with an intervening brief lag-phase are recognized during the growth of the metacercaria of Pleurogenoides orientalis in the intermediate host (nymphs of Tramea limbata), the first phase being characterized by rapid growth and organogeny and the second phase by limited growth and development. The phases of growth and development of the metacercaria are correlated with various events in the cyst-forming process. The growth of the adult fluke in the definitive host (Rana cyanophlyctis) is characterized by a short initial lag-phase followed by a rapid phase during which there is rapid growth. Comparison of allometric growth parameters of various organs of the metacercaria and of the adult revealed definite allometric shifts. The validity of various species included in the genus Pleurogenoides is examined in the light of observations made on intraspecific variation in P. orientalis.     

On the systematic position of Ophiosacculus Macy, 1935 (digenea: Lecithodendriidae), with the erection of the Ophiosacculinae n. subfam

The phylogenetic relationships and systematic position of the digenean genus Ophiosacculus Macy, 1935 has been controversial and opinions of different authors on its systematic position and content are contradictory. Molecular analysis based on the partial sequences of the large subunit ribosomal DNA gene of the type and only valid species of the genus, Ophiosacculus mehelyi (Mödlinger, 1930), as well as previously published sequences of members of several families of Plagiorchiata (including the Allassogonoporidae, Lecithodendriidae and Pleurogenidae as potential relatives of Ophiosacculus) has shown that Ophiosacculus forms a clade with the typical representatives of the Lecithodendriidae from bats. Ophiosacculus is basal to the cluster containing Lecithodendrium, Prosthodendrium and Pycnoporus and has quite pronounced differences in the sequenced fragment compared to these genera. Based on the results of the molecular study, morphological characteristics of Ophiosacculus (in particular, possession of a seminal vesicle lying freely in parenchyma) and the fact that the type-specimen of Gyrabascus brevigastrus Macy, 1835 (type-species of the monotypic genus Gyrabascus and type-genus of the subfamily Gyrabascinae) belongs to Allassogonoporus, a new subfamily, the Ophiosacculinae, with Ophiosacculus as the type-genus, is established within the Lecithodendriidae. Molecular study did not support a close phylogenetic relationship between Allassogonoporus and Ophiosacculus, although several authors previously allocated both these genera to the Allassogonoporidae. Morphological study revealed the position of the genital pore in O. mehelyi to be at the posterior margin of the ventral sucker. An amended diagnosis of Ophiosacculus and a diagnosis of Ophiosacculinae n. subfam. are given.     

The miracidium microanatomy of Philophthalmus rhionica (Trematoda: Philophthalmidae)

The study of ultrastructure of Philophthalmus rhionica miracidium was carried out. Update the ultrastructures of miracidium were studied in a restricted number of species belonging to the families Notocotylidae, Paramphistomatidae, Sanguinicolidae, Fasciolidae, Schistosomatidae (Galaktionov, Dobrovolsky, 1998). The ultrastructure of representatives of two latter families, Fasciola hepatica and Schistosoma mansoni respectively, have been examined most carefully. The family Philophthalmidae differs from the families Fasciolidae and Schistosomatidae by the aberrant pedogenetic miracidium.     

The life cycle of Echinochasmus bagulai (Trematoda: Echinostomatidae)

The life history of Echinochasmus bagulai, an echinostomatid trematode in birds, is reported and stages in the life cycle are described. Natural infections with cercariae, which are of the gymnocephalous type, were found in the thiarid snail Thiara tuberculata. Metacercarial cysts were found in the gills of Aplocheilus panchax, Oryzias melastigma, Gambusia affinis and Channa punctata. Adults were obtained in the small intestine of Ardeola grayi. In laboratory experiements development of cercariae into infective metacercariae took 10 days in the gills of A. panchax. Mature flukes were recovered in 10 days in the small intestine of experimentally infected 1-day-old leghorn chicks. The eggs collected from the faeces of these infected chicks were incubated at 39 degrees C. The free-swimming miracidia were found on the fifth day of incubation.     

The family prosthogonimidae (Trematoda) in Australia

The family Prosthogonimidae (Trematoda) in Australia. International Journal for Parasitology 3: 853–862. The family Prosthogonimidae has previously been known in Australia by three species of Prosthogonimus Lühe, 1899 (from birds) and by Coelomotrema Angel, 1970 (from marsupials). Two new genera are now proposed: Cylindrotrema cygni from Cygnus atratus (Latham) (caecum), and Mawsonotrema eudyptulae from Eudyptula minor (Forster) (liver). Prosthogonimus vitellatus Nicoll, 1914 is recorded from three new hosts, Gymnorhina tibicen leuconota (Latham), Phalacrocorax melanoleucos (Vieillot) and Chlidonias hybrida (Pallas), and the species is redescribed from 11 specimens from the first of these. The life history, not known for any Australian species, is discussed.

The only plump-bodied genera in the family are Coelomotrema, Cylindrotrema and Mawsonotrema, all of which are confined to Australia.

Mawsonotrema differs from all other members of the family in the position of the genital pore, which is away from the anterior end of the body, lying against the anterior border of the acetabulum.     

The life cycle of Euclinostomum heterostomum (Rudolphi, 1809) (Trematoda: Clinostomatidae)

In small forest streams of West Nigeria the snail species Bulinus globosus was found to be the first intermediate host of a clinostomatid species which proved in successful infection experiments with the cichlid fish Tilapia zillii as second intermediate host to be Euclinostomum heterostomum (Rudolphi, 1809). Final hosts are herons. The morphology of the redia and the morphology and behaviour of the cercaria are described for the first time. The metacercaria which settles dorsal to the swim-bladder or in the kidney of the host fish requires more than two months (at tropical temperatures) for full development. Histological sections of the metacercaria revealed that its pharynx is provided with only few muscle fibres but surrounded by many myoblast-like cells, and the fact that the interior surface of this organ has a dense brush-like lining consisting of long microtriches. The pathology of infected fish is briefly described, and remarks about the geographical distribution of the parasite are given.     

Egg and miracidium of Hirudinella ventricosa (Trematoda: Hirudinellidae)

It is reported for the first time that Hirudinella ventricosa releases eggs in strings, each string containing active spermatozoa and numerous oval, thick-shelled, translucent eggs measuring 40-42 x 28-30 microns. Each egg contained a fully developed miracidium with an anterior crown of spines.