Molecular characterization revealed Fasciola specimens in Ecuador are all Fasciola hepatica,none at all of Fasciola gigantica or parthenogenic Fasciola species

All 225 Fasciola flukes obtained from domestic animals (73 cattle, 7 sheep and 1 pig) of 18 distinct geographic areas in Ecuador-South America, were identified as Fasciola hepatica, based on molecular analyses of nuclear pepck and pold genes, and mitochondrial nad1gene as well as the morphological observation of sperm within the seminal vesicles. Fasciola gigantica and parthenogenic Fasciola forms endemic to Asian countries were not found in this study, although zebu cattle and water buffalos have introduced into South America from Asia; this could be due to the absence of suitable intermediate host snails. The results of pepck analysis using multiplex PCR developed previously showed that 32 of the flukes could not be confirmed as F. hepatica, suggesting that the method is unreliable for the accurate discrimination of F. hepatica, and that pepck gene of the species consists of multiple loci, not a single locus. The results of genetic diversity, phylogenetic, and network analyses based on mitochondrial nad1 sequences suggest that F. hepatica populations in South America, including Ecuador, formed from the ancestral F. hepatica individuals introduced into the continent along with anthropogenic movement of livestock infected with the species.     

Characterization of Fasciola samples by ITS of rDNA sequences revealed the existence of Fasciola hepatica and Fasciola gigantica in Yunnan Province, China

On mainland China, liver flukes of Fasciola spp. (Digenea: Fasciolidae) can cause serious acute and chronic morbidity in numerous species of mammals such as sheep, goats, cattle, and humans. The objective of the present study was to examine the taxonomic identity of Fasciola species in Yunnan province by sequences of the first and second internal transcribed spacers (ITS-1 and ITS-2) of nuclear ribosomal DNA (rDNA). The ITS rDNA was amplified from 10 samples representing Fasciola species in cattle from 2 geographical locations in Yunnan Province, by polymerase chain reaction (PCR), and the products were sequenced directly. The lengths of the ITS-1 and ITS-2 sequences were 422 and 361-362 base pairs, respectively, for all samples sequenced. Using ITS sequences, 2 Fasciola species were revealed, namely Fasciola hepatica and Fasciola gigantica. This is the first demonstration of F. gigantica in cattle in Yunnan Province, China using a molecular approach; our findings have implications for studying the population genetic characterization of the Chinese Fasciola species and for the prevention and control of Fasciola spp. in this province.     

The structure and cytochemistry of the neurosecretory cells of Fasciola gigantica Cobbold and Fasciola hepatica L.

Histochemical studies of the nervous system of Fasciola gigantica and Fasciola hepatica were undertaken. Neurosecretory cells were detected by Gomori's aldehydefuchsin, Bargmann's chrome hematoxylin-phloxin, Mallory's triple stain, periodic acid-Schiff, Heidenhain's Azan and alcian blue after potassium permanganate oxidation. Two types of neurosecretory cells were recognized and designated as "A" and "B". Type "A" cells occurred in small numbers in the brain and subesophageal mass and type "B" cells ubiquitous in distribution. The reactions of these cells to the standard stains for neurosecretory substance generally, were less intense than the neurosecretory cells of other animals such as crustaceans and insects. The structure, organisation, distribution and cytochemistry of neurosecretory cells in Fasciola gigantica and Fasciola hepatica is discussed.     

Composition and metabolism of phospholipids of Fasciola hepatics, the common liver fluke.

1. The phospholipid composition of Fasciola hepatica, the common liver fluke, was compared to that of the liver of the host animals (rats and cattle). Considerable differences were found:monoacyl-sn-glycero-3-phosphorylcholine, hardly detectable in the liver, was found in significant amounts in the parasite. On the other hand, sphingomyelin, a normal constituent in the liver, appears to be absent in the liver fluke. Fasciola hepatica isolated from rat and cow liver had a strikingly similar phospholipid composition. 2. Qualitative and quantitative differences were also found between the fatty acyl constituents of the phospholipids of the parasite and the liver. The major difference was the presence of eicosaenoic and eicosadienoic acids in the parasite, whereas these acids were not detected in the liver. 3. In vitro incubations of Fasciola hepatica in the presence of (32P)phosphate and (2-3H)glycerol resulted in the labelling of all phospholipids of the parasite, except that the 3H label did not incorporate into ethanolamine plasmalogen. This is in agreement with the concept that in animals, glycerol is introduced into plasmalogens via dihydroxyacetonephosphate. 4. Homogenates of liver flukes were found to catalyze the synthesis of phosphatidylcholine from 1,2-diacyl-sn-glycerols and CDPcholine. 5. These results strongly suggest that Fasciola hepatica is capable of synthesizing at least part of its fatty acids and phospholipids.     

Phenotypic analysis of adults of Fasciola hepatica, Fasciola gigantica and intermediate forms from the endemic region of Gilan, Iran

Fascioliasis is an important human and animal disease caused by Fasciola hepatica and Fasciola gigantica. In Iran, the distribution of these two species overlaps in most areas, including the northern human endemic province of Gilan where both fasciolids are simultaneously found in individual cattle and buffaloes. A phenotypic study of fasciolid adult flukes from naturally infected bovines from Gilan was carried out by means of an exhaustive morphometric analysis using traditional microscopic measurements and an allometric model. The Iranian fasciolids were compared to F. hepatica and F. gigantica standard populations, i.e. from geographical areas where both species do not co-exist (Bolivia and Burkina Faso, respectively). Although morphometric values somewhat overlapped, there were clear differences in allometric growth. The allometric function was adjusted to 25 pairs of variables. Results obtained revealed that Iranian F. hepatica-like specimens are larger than the F. hepatica standard and Iranian F. gigantica-like specimens are longer and narrower than the F. gigantica standard, but with smaller body area. Measurements which permit a specific differentiation in allopatric populations (distance between ventral sucker and posterior end of the body; ratio between body length and body width) overlap in the specimens from Gilan, thus proving the presence of intermediate forms. When compared to the standard populations, the different Iranian fasciolid morphs show greater differences in F. gigantica-like specimens than in F. hepatica-like specimens. This study shows that simple, traditional microscopic measurements may be sufficient for the morphometric characterisation of fasciolids, even in areas where intermediate forms are present.     

Surface features, sensory structures, and movement of the newly excysted juvenile Fasciola hepatica L.

Three types of presumed sensory endings were distinguished by scanning electron microscopy: a ciliated type, a domed type, and a pit. The ciliated and domed type were also serially sectioned for transmission electron microscopy. Six of the pit type were observed, a group of 3 on each side of the oral sucker. The ciliated type were found only among the tegumental spines, and on the anterior ventrolateral surfaces except for an anterodorsal pair. The domed type resembled the ciliated type in that it had a ciliary basal body and rootlet but it lacked a cilium. It was found only in the tegument above the suckers where it probably serves as a pressure or contact receptor. Movement in vitro occurred by alternate attachment and release of the suckers with a vermiform peristalsis and the rings of spines between the suckers were considered to aid this movement in vivo.     

Studies on the viability of metacercariae of Fasciola gigantica.

The viability of metacercariae of Fasciola gigantica was tested by in vitro and in vivo methods. In vitro testing was based upon the motility of juvenile flukes within the inner cyst as examined under the light microscope. In vivo testing was undertaken through experimental infections of rabbits (two groups) and natural definitive hosts, lambs (one group). In the first group, out of six rabbits each given 25 metacercariae, worm establishment only took place in one rabbit with a single fluke recovery on 60 days post infection. In the second group of six rabbits each given 200 metacercariae, five were infected, with two or three flukes per host. All the lambs given 250 metacercariae became infected showing prevalences of 7.2-40% in comparison with rabbits in which low prevalences (0-4%) were recorded. The results indicated that even viable metacercariae which were already tested in vitro could not readily establish in rabbits. Such variability in worm establishment suggests that immunological and chemotherapeutic studies in rabbits infected with F. gigantica are likely to be unreliable.     

Molecular analyses confirm the coexistence of Fasciola gigantica and parthenogenetic Fasciola in the Philippines

Fasciola flukes collected from domestic buffalos and cattle in the Philippines were confirmed as Fasciola gigantica and parthenogenetic Fasciola based on DNA analyses of nuclear pepck and pold genes, and the mitochondrial ND1 gene. This study is the first to elucidate that F. gigantica and parthenogenetic Fasciola coexist in the Philippines with prevalences of 90.6% and 9.4%, respectively. The F. gigantica population showed a high genetic diversity with 25 ND1 haplotypes, suggesting that F. gigantica has existed in the Philippines for a long time. In contrast, parthenogenetic Fasciola flukes showed a single ND1 haplotype (Fsp-ND1-P1), which was identical to the founder haplotype, Fg-C2 of parthenogenetic Fasciola in China. These results indicate that parthenogenetic Fasciola in the Philippines is a recently introduced population from a neighboring continent.     

Fasciola hepatica: the ultrastructure of the epithelium of the seminal vesicle, the ejaculatory duct and the cirrus.

The ultrastructure of the seminal vesicle, ejaculatory duct, cirrus sac and cirrus is described. The epithelium of the seminal vesicle consists of a single layer of squamous to cuboidal cells. The apical ends of the cells have thin polymorphic lamellae and long narrow pits, both of which enclose normal spermatozoa. The cells have a moderate amount of GER and Golgi complexes which produce a lucid secretory body. The ejaculatory duct epithelium is composed of cuboidal to columnar cells between or through which project the terminal parts of the ducts of the unicellular prostate glands. The apical surfaces of the epithelia are extended into triangular or filiform projections having thin sinuous lamellae. The cytoplasm contains GER cisternae and Golgi complexes which synthesize a dense ovoid secretion. The cirrus sac and cirrus are covered by a thin modified tegument. The cirrus has many spines and the normal ratio of T1 and T2 type of secretory bodies, whereas the cirrus sac has few spines and the T2 type of secretory body predominates over the T1 type. The significance and possible functions of the structures observed in the three tissues are discussed.     

Age-dependent infectivity of orally transferred juvenile Fasciola hepatica.

Juvenile Fasciola hepatica is infective when administered orally. To determine whether the age of juveniles is a factor in infectivity by oral transfer, experimental mice were challenged orally with immature F. hepatica that had been grown in donor mice for 12, 14, 16, and 18 days. Experimental mice were examined for infections 12 16 days after the oral transfers. The infection success in experimental mice decreased with the age of juveniles. The worm recovery also decreased according to the age of juveniles. None of the juveniles was infective when grown for longer than 11 days. Once infected, orally transferred worms continued to grow. Juvenile age was a significant factor in determining the infectivity of orally transferred juvenile F. hepatica.     

Isolation and partial sequencing of a pancreatic polypeptide-like neuropeptide from the liver fluke, Fasciola hepatica.

1. A pancreatic polypeptide (PP)-immunoreactive neuropeptide has been isolated and partially sequenced from the liver fluke, Fasciola hepatica. 2. Gel permeation chromatography of an acid ethanol extract of cattle flukes showed that the peptide is similar in size to mammalian (bovine) PP. 3. The Fasciola peptide was purified to homogeneity by means of reverse-phase HPLC, employing different column chemistries. 4. The purified peptide was sequenced using automated gas-phase Edman degradation and the first 24 amino acid residues determined.     

Fasciola hepatica: basal infolds and associated vacuoles of the tegument.

The tegument of Fasciola hepatica has been shown to contain long invaginations of its basal plasma membrane, hereafter called basal infolds. Associated with the membranes of the infolds, and with the apical and basal plasma membranes, is a Na⁺ K⁺ ATPase (EC 3.6.1.3). Furthermore, polymorphic masses of acid mucopolysaccharide lie close to or against the sides of the infolds and the basal plasma membrane and also fill cytoplasmic tubules which connect the tegument with the tegumental cells. Fixation and incubation of flukes in hypertonic and hypotonic media have shown that the infolds respond to changes in external osmolarity by collapsing in the former and swelling in the latter. This is not simply a passive response, however, since the infolds return to near normal configuration and morphology within 1 hr in either hypertonic or hypotonic media, even though the whole fluke may be shrunken or turgid depending on medium osmolarity. The tegument, therefore, has many of the characteristics of a transporting epithelium. A theory outlining the possible mode of operation of the tegument as a transporting epithelium is proposed on the basis of the present structural, chemical, and physiological findings combined with current ideas of the role and functioning of standing gradients, and forward and backward channel systems in other transporting epithelia.     

The electron transport systems of Fasciola hepatica mitochondria.

The electron transport systems of Fasciola hepatica mitochondria were investigated spectrophotometrically at room temperature and at −196°. The mitochondria were found to contain substrate reducible a-, b- and c-type cytochromes. All of the cytochrome components of the classical mammalian type of respiratory chain were present, although the concentration of cytochromes aa₃ was low. In addition to the mammalian type of respiratory chain, the Fasciola mitochondria contained a substrate reducible b-type cytochrome component (557 nm) which included a CO reactive o-type cytochrome. The results suggest that F. hepatica mitochondria contain a branched electron transport system including a mammalian type of chain and involving two terminal oxidases and at least two b-type cytochromes.