Parasiticidal effects of peroxynitrite on ovine liver flukes in vitro

Peroxynitrite (ONOO-) is a cytotoxic anion, produced by interaction between nitric oxide and superoxide in vivo in some inflammatory cells. This study investigated its effects on Fasciola hepatica and Dicrocoelium dendriticum isolated from ovine livers and kept in bile at room temperature. Peroxynitrite was synthesized using a quenched flow reactor and assayed spectrophotometrically. It was applied at different concentrations (10(-3.5) to 10(-2.3 M)) to the flukes kept in bile. The viability of the peroxynitrite-treated flukes was compared with a control group (n=5-7 per group). Control F. hepatica and D. dendriticum lived for 226+/-11and 208+/-14min, respectively. Life times were decreased by peroxynitrite at all concentrations used (P<0.001). At the highest concentration of peroxynitrite, F. hepatica and D. dendriticum lived only for 6.1+/-0.4 and 4.1+/-4.1+/-0.2min, respectively. Correlation between peroxynitrite concentration and parasite viability was significant in the case of F. hepatica (r= -0.842; P= 0.0035). A single application of peroxynitrite can decrease the life span of ovine liver flukes. A failure in the activation of hepatic macrophages in infected animals may lead to a decreased production of free radicals and, thus, peroxynitrite. Such a failure is likely to deprive the body of a defence tool against multicellular parasites.     

Fasciola hepatica: an antigen fraction derived from newly excysted juveniles, containing an immunoreactive 32-kDa protein, induces strong protective immunity in rats

Crude antigens of adult Fasciola hepatica and of newly excysted juveniles (NEJ) and a low-molecular-weight fraction of antigen from NEJs were tested for inducing protective immunity in rats. Two routes of vaccination were applied. The results showed that intraperitoneal vaccination induced significantly better protection (P <0.05) than intramuscular vaccination. Intraperitoneal vaccination with antigens from NEJs induced more effective protection: after challenge infection, rats that were so vaccinated had 92.6% (+/-2.5% SEM) fewer parasites in their liver and 57.3% (+/-13.3% SEM) fewer parasites penetrating the gut wall than control rats. Rats that were vaccinated with a low-molecular-weight fraction of antigen from NEJs were also highly protected against a challenge. F. hepatica antigens that are immunoreactive were identified on immunoblots, using sera collected from highly protected rats that had been vaccinated with NEJ antigens and also sera from cattle and rats that were experimentally infected with F. hepatica. The low-molecular-weight fraction of antigen from NEJs contained an immunodominant 32-kDa protein that was recognized by serum antibodies of vaccinated rats and immune cattle. This 32-kDa protein was not detected in partially purified antigens from adult flukes. We conclude that antigens of NEJs of F. hepatica, when injected intraperitoneally in rats, are highly protective. In particular, the 32-kDa protein contained in these antigens may be highly valuable for the development of an effective vaccine against F. hepatica.     

Fasciola hepatica: site of resistance to reinfection in cattle

The effective site of resistance to reinfection of cattle with Fasciola hepatica was examined by recovery of challenge flukes from either the liver or body cavity. Calves infected 18 or 26 weeks previously with F. hepatica showed levels of resistance to reinfection of 56 and 94%, respectively, as assessed by recovery of flukes from the liver 15-16 weeks after challenge. Plasma glutamate dehydrogenase (EC 1.4.1.3; GLDH) enzyme activity estimations revealed only a marginal increase in these latter resistant calves compared with previously naive controls, indicating minimal liver damage as a result of migrating flukes. By comparison, when immature challenge flukes were recovered from the body cavity 4 or 14 days after infection of corresponding previously infected or naive calves, there was no significant difference in numbers. It appears, therefore, that, in cattle, resistance mechanisms are effective against challenge flukes at or soon after penetration of the liver.     

An ultrasensitive capture ELISA for detection of Fasciola hepatica coproantigens in sheep and cattle using a new monoclonal antibody (MM3)

A capture enzyme-linked immunosorbent assay (ELISA) using a new monoclonal antibody (mAb MM3) is reported for the detection of Fasciola hepatica excretory-secretory antigens (ESAs) in feces of infected hosts. The mAb MM3 was produced by immunization of mice with a 7- to 40-kDa purified and O-deglycosylated fraction of F. hepatica ESAs, which has previously been shown to be specific for the parasite. The specificity and sensitivity of the MM3 capture ELISA were assessed using feces from sheep and cattle. Sheep feces were obtained from a fluke-free herd (with most animals harboring other nematodes and cestodes), from lambs experimentally infected with 5-40 F. hepatica metacercariae and in some cases treated with triclabendazole at 14 wk postinfection (PI), and from uninfected control lambs. Cattle feces were collected at the slaughterhouse from adult cows naturally infected with known numbers of flukes (from 1 to 154) or free of F. hepatica infection (though in most cases harboring other helminths). The MM3 capture ELISA assay had detection limits of 0.3 (sheep) and 0.6 (cattle) ng of F. hepatica ESA per milliliter of fecal supernatant. The assay detected 100% of sheep with 1 fluke, 100% of cattle with 2 flukes, and 2 of 7 cattle with 1 fluke. The false-negative animals (5/7) were probably not detected because the F. hepatica individuals in these animals were immature (5-11 mm in length). As expected, coproantigen concentration correlated positively (r = 0.889; P < 0.001) with parasite burden and negatively (r = 0.712; P < 0.01) with the time after infection at which coproantigen was first detected. Nevertheless, even in animals with low fluke burdens (1-36 parasites), the first detection of F. hepatica-specific coproantigens by the MM3 capture ELISA preceded the first detection in egg count by 1-5 wk. In all sheep that were experimentally infected and then untreated, coproantigen remained detectable until at least 18 wk PI, whereas in sheep that were experimentally infected and then flukicide treated, coproantigen became undetectable from 1 to 3 wk after treatment. None of the fecal samples from sheep or cattle negative for fascioliasis but naturally infected with other parasites including Dicroelium dendriticum showed reactivity in the MM3 capture ELISA. These results indicate that this assay is a reliable and ultrasensitive method for detecting subnanogram amounts of F. hepatica antigens in feces from sheep and cattle, facilitating early diagnosis.     

The relationship between normocytic, hypochromic anaemia and iron concentration together with hepatic enzyme activities in cattle infected with Fasciola hepatica

Erythrograms determined from whole blood analyses and serum analyses for aspartate aminotransferase (AST), gamma-glutamyl transpeptidase (GGT) and alkaline phosphatase (ALP) activities, and iron concentration, were used in infected and uninfected cattle to determine the type of anaemia and degree of hepatic damage caused by Fasciola hepatica. Blood samples from 86 infected and 30 uninfected cattle were taken at slaughter. Haematological analyses revealed decreased levels of packed cell volume (PCV), haemoglobin concentration, mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC) in infected compared with uninfected cattle (P < 0.05). A decrease in the concentration of serum iron was also observed in infected cattle compared with uninfected cattle (P < 0.05). Significant increases in AST, GGT and ALP activities were observed in cattle infected with F. hepatica when compared with uninfected cattle (P < 0.05). It was concluded that the anaemia observed in cattle infected with F. hepatica is a normocytic, hypochromic anaemia and the most important aetiology of the anaemia is the chronic blood loss due to the blood-sucking activity of the adult flukes and leakage of blood from the bile duct to the intestine, which results in iron deficiency. The increased activities of serum enzymes indicated chronic hepatic and bile duct injuries associated with chronic infection with F. hepatica.     

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.     

Glutathione S-transferase. Novel vaccine against Fasciola hepatica infection in sheep

The potential of GST as a vaccine candidate against liver fluke infection in ruminants was studied by vaccinating sheep (n = 9) with GST purified from adult worms of Fasciola hepatica and challenging with 500 F. hepatica metacercariae. The immunization induced a high antibody response to GST in contrast to the poor or undetectable response to this Ag observed in naturally infected sheep. Throughout the trial, the progress of the fluke infection was monitored by measuring RBC hemoglobin levels, the extent of liver damage and the fecal egg output in the sheep. This analysis indicated that a subpopulation (n = 4) of the GST vaccinated animals exhibited no anemia, reduced liver damage and a lower mean fecal egg count relative to the infected control group suggesting a lower fluke burden in these animals. Worm burdens in the livers of the GST vaccine group (107 +/- 22) were 57% lower than in the infected control group (250 +/- 25). The subpopulation of the GST vaccine group demonstrated a 78% reduction in mean worm burdens relative to the control group. These results show that GST of adult F. hepatica is a novel Ag that can significantly protect sheep against liver fluke infection. The results suggest that the immune response to GST is directed to the juvenile worm reducing the number of worms that can establish in the liver of the vaccinated animals.     

Early immunodiagnosis of fasciolosis in ruminants using recombinant Fasciola hepatica cathepsin L-like protease

A diagnostic ELISA with recombinant Fasciola hepatica cathepsin L-like protease as antigen was developed to detect antibodies against F. hepatica in sheep and cattle. The recombinant cathepsin L-like protease was generated by functional expression of the cDNA from adult stage F. hepatica flukes in Saccharomyces cerevisiae. Specificity and sensitivity of the cathepsin L enzyme-linked immunosorbent assay (ELISA) was assessed using sera from sheep and calves experimentally or naturally mono-infected with F. hepatica and six-seven other parasites. The sensitivity of the cathepsin L ELISA for sheep and cattle sera was 99.1 and 100%, respectively. In the experimental setting with established mono-infections, the specificity of the cathepsin L ELISA was 98.5% for cattle sera and 96.5% for sheep sera. In experimentally infected cattle and sheep, the first detection of F. hepatica-specific antibodies appeared first between 5 and 7 weeks post-infection, but depended on the infectious dose of F. hepatica. In ELISA the detection preceded first detection of the infection based on egg counts and remained detectable till at least 23 weeks after a primary F. hepatica infection. Detection of Fasciola gigantica infections was similar to detection of F. hepatica. The first detection occurred at week 5 and signals persisted for at least 20 weeks. All sera from naturally F. hepatica infected sheep were seropositive in the cathepsin L-like ELISA. The relevance of this ELISA format was also evaluated using sera from naturally infected cattle in the Netherlands, Ecuador and Vietnam and compared with results from egg-counts. For the latter two endemic areas with mixed parasitic infections the 'apparent' sensitivity of the cathepsin L ELISA was calculated for all serum samples together to be 90.2%. The 'apparent' specificity under these conditions was calculated to be 75.3%. In cattle, the cathepsin L ELISA was superior to the concurrently evaluated peptide ELISA format using a single epitope as the antigen both in controlled natural infections as well as in infections in endemic areas. The present ELISA-format contributes a relatively sensitive and reliable tool for the early serodiagnosis of bovine and ovine fasciolosis.     

Detection of antibodies in wild ruminants to evaluate exposure to liver trematodes

Wild ruminants sharing pastures with domestic livestock are at risk of infection by liver trematodes. Detection of antibodies provides a very useful tool to gain more knowledge about the distribution of these parasites. Non-lethal methods are strongly encouraged for the analysis of the risk of infection among wild ruminants. A seroepidemiological survey was conducted to analyze exposure to hepatic trematodes ( Fasciola hepatica and Dicrocoelium dendriticum ) in wild ruminants from southern Spain. Blood samples were collected from 69 bovids (Mouflon + Spanish ibex) and 143 cervids (red deer + fallow deer) from Sierra de Cazorla, Segura and Las Villas Natural Park. The samples were analyzed using the excretory/secretory antigens of each trematode to determine the IgG response. All the animals were examined at necropsy for the presence of flukes, and the species, age, and gender of the animals were recorded. Fasciola hepatica were only observed in cervids (3%; 95% confidence interval [CI] = 2-8), while D. dendriticum specimens were recorded in 1% (0-8) of bovids and 4% (CI = 2-9) of the cervids. The IgG-seroprevalence against F. hepatica was significantly higher in the cervids. Statistical differences according to gender were observed. The bovids exhibited the greatest percentages of positive cases to D. dendriticum antigens, and the DdES-seroprevalence was related to age of the animals. When considering all the factors, the FhES-seroprevalence was initially distributed according to the type of ruminant (cervids), gender (male), and age (>2 yr).     

Identification of Fasciola species isolated from Egypt based on sequence analysis of genomic (ITS1 and ITS2) and mitochondrial (NDI and COI) gene markers

Fascioliasis has a negative impact on the farming industry in both developed and developing countries, rather than a public health challenge. This study was performed to identify Fasciola sp. from different definitive hosts (buffalo, cattle, and sheep) based on the molecular parameters and spermatogenesis. Ninety-one adult flukes were collected from livers of slaughtered animals at abattoirs in different prefectures in Egypt. Microscopic examination of the analyzed flukes showed many normal spermatozoa in the seminal vesicles (spermic), suggesting that they have the ability of spermatogenesis. This study showed that no parthenogenic Fasciola species occurred in Egypt. Molecular analysis was performed utilizing genomic (ITS1 and ITS2) and mitochondrial (NDI and COI) gene markers. Whereas 16 animals proved to have infection with a single Fasciola species, 2 were infected with both F. hepatica and F. gigantica. The results indicated that sheep were prone to F. hepatica (8 out of 10 animals) more than F. gigantica infection. Sequences of ITS1 and ITS2 ribosomal region indicated that the flukes were categorized into 3 groups F. hepatica-type (47), F. gigantica-type (42) and 2 flukes possessed sequences of both types indicating an existence of different alleles at the same loci. Unique overlapping of T/C bases were detected in both ITS1 (Position 96) and ITS2 (Position 416). Based on results of mitochondrial gene markers (NDI and COI), flukes were classified into F. hepatica-type and F. gigantica-type. Extensive intra-sequence polymorphism was detected at both markers. NDI and COI sequences of Egyptian strain of F. gigantica showed pronounced diversity compared with relevant sequences at database.     

The fate of Fasciola hepatica metacercariae following challenge infection of immune rats

Groups of rats, infected 7 weeks previously with Fasciola hepatica, together with appropriate control groups, were challenged either orally or intraperitoneally with 30 metacercariae. The mean worm recovery from the previously infected, orally challenged rats was significantly lower than from their respective controls (2.2 +/- 1.1 worms as opposed to 9.0 +/- 2.6). There was no significant difference in mean worm recovery from the previously infected, intraperitoneally challenged rats and their respective controls (5.3 +/- 3.2 worms as opposed to 6.2 +/- 1.9). Livers of the orally challenged group appeared to be largely free from secondary damage but considerable damage was evident in rats which received an intraperitioneal challenge. This evidence supports the view that the gut acts as an important barrier to metacercariae of a challenge infection. In a further experiment, young flukes were recovered from the gut, abdominal cavity and liver of immune and control rats 9, 18, 27, 36 and 45 h after oral challenge. It was found that fewer flukes successfully penetrated the guts of immune rats (3%) than those of uninfected controls (13%), again pointing to the gut as a barrier to metacercariae of a challenge infection. Protective mechanisms that may operate at the level of the gut are discussed.     

Experimental fascioliasis in the rat-like hamster,Tscherskia triton,and other rodent hosts

Experimental infection with Fasciola hepatica and parthenogenetic Fasciola sp. in laboratory animals have been conducted in rats and rabbits. Inoculation of less than 5 metacercariae into rat-like hamsters, Tscherskia triton, is sufficient to establish Fasciola infections. The prepatent period of F. hepatica and the parthenogenetic Fasciola sp. in T. triton was shorter than that in rats and rabbits, suggesting that T. triton is a suitable experimental model for these flukes. In contrast, F. gigantica infection in T. triton did not yield adult flukes; T. triton, is therefore, considered to be an unsuitable host for F. gigantica. The cotton rat, Sigmodon hispidus, was an unsuitable host for the parthenogenetic Fasciola sp.     

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.     

DNA-based identification of a hepatic trematode in an elk calf

Liver fluke infection was identified as a probable cause of clinical disease in an approximately 6-mo-old elk (Cervus elaphus) in coastal Oregon. Clinical pathology and necropsy findings are described. The alcohol-fixed flukes that were submitted for identification were similar in size to Fasciola hepatica, but their shape resembled Fascioloides magna in that they lacked a distinctive anterior cone. A few structures consistent with the eggs of F. magna were observed in liver lesions, suggesting that at least some of the worms were sexually maturing. Due to difficulties in morphologic identification associated with improper fixation technique, DNA analysis was used to compare small subunit (SSU) and internal transcribed spacer 2 ribosomal RNA gene sequences of the recovered parasites with those of F. hepatica and F. magna, confirming these small, but sexually mature flukes were F. magna. This is the first publication of the SSU gene sequence for F. magna. Phylogenetic analysis showed that it is related to, but is an outlier, to the genus Fasciola. Due to the high mortality rate associated with this disease outbreak, the overall significance of trematodiasis in the herd is unclear.     

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.     

Allopatric combination of Fasciola hepatica and Lymnaea truncatula is more efficient than sympatric ones

Parasites are capable of rapid evolutionary changes relative to their hosts, due to short life cycle, short generation time, and high fecundity. The direction of the evolution of parasite virulence can be studied in cross-transfer experiments, combining hosts and parasites from different localities, and comparing the outcome of established (sympatric and potentially locally adapted) and novel (allopatric) combinations of hosts and parasites. We aimed to compare the compatibility with snails hosts, the infectivity of metacercariae in rabbits and rats, and the fitness among different combinations (French-FF and Spanish-SS sympatries and allopatry-FS). The first isolate of Fasciola hepatica and its corresponding intermediate host, Lymnaea truncatula originated from Lugo's northwestern Spain. The second isolate of parasite and snail was collected in the Limoges area in central France. The Spanish snails were more susceptible to their sympatric trematode than the French snails. The Spanish flukes were more infective to intermediate hosts (snails) than the French flukes, but subsequent definitive hosts (rats or rabbits) infections remained similar. The estimated fitness was low in sympatric infections and highly similar (from 4.7 to 5.3). The fitness similarity corresponds, however, to different variations in life-history traits that could represent different strategies among the host-parasite local combinations. The infection rate in snails, metacercarial productivity, metacercarial infectivity, and the estimated fitness were better for allopatric combination (FS). The susceptibility data showed a higher efficiency of flukes in the allopatric snail population than in their local snail population. However, our results were obtained after one generation and from a single isolate and it remains to be determined if all allopatric fluke-snail isolates may present a better fitness. Nevertheless our results indicate that introduction of liver fluke-infected cattle should be monitored carefully, as it could result in the introduction of more efficient parasites.     

Human fascioliasis and the presence of hybrid/introgressed forms of Fasciola hepatica and Fasciola gigantica in Vietnam

The two species common of liver fluke, Fasciola hepatica and Fasciola gigantica, cause human fascioliasis. Hybrids between these species, and introgressed forms of Fasciola, are known from temperate and subtropical regions of eastern Asia. Here, we report the presence of hybrid and/or introgressed liver flukes in Vietnam where it has recently been recognised that human fascioliasis is an important zoonotic disease. Specimens examined came from domestic stock (cattle and buffalo) at slaughter and also from human patients. DNA sequences were obtained from the nuclear ribosomal second internal transcribed spacer (ITS-2) and from portions of two mitochondrial protein-coding genes. Mitochondrial sequences in every case were similar to those of Fasciola gigantica. Nuclear ITS-2 sequences belonged to one or other of the Fasciola species, or, sequences from both were found in the same individual worm. This study extends the known range of hybrids or introgressed forms of Fasciola into tropical regions of Asia.     

肝片形吸虫对肝纤维化的影响及治疗

作为一种可同时感染家畜和人类的寄生虫,肝片形吸虫对人类和家畜的身体机能造成了不可修复的损伤,在世界范围内造成了巨大的经济损失,尤其是感染早期对肝脏造成的肝纤维化症状不明显,不易被发现。本文主要综述了肝片形吸虫、肝纤维化、三氯苯哒唑的相互关系,并从Th1、Th2类细胞因子、T细胞、血红素氧合酶-1(heme oxygenase 1, HO-1)、巨噬细胞等几个方面探讨了肝片形吸虫对大鼠肝纤维化的影响,包括细胞间的相互作用以及它们所诱导的细胞因子(如:IL-4、IL-10、IFN-γ、TNF-α等)对肝纤维化的促进或抑制作用。最后,还综述了当前唯一可以治疗人类和家畜寄生虫感染的药物三氯苯哒唑对肝片形吸虫所致肝纤维化的治疗作用。     

Comparison of adult liver flukes from highland and lowland populations of Bolivian and Spanish sheep

A morphological study of adult liver flukes and eggs from sheep in a human fascioliasis endemic zone in the Northern Bolivian Altiplano showed that they belong to the species Fasciola hepatica. An exhaustive morphometric comparison with a F. hepatica population from Spanish sheep was made using image analysis and an allometric model: (y2m-y2)/y2 = c(y1m-y1)/y1[b, where y1 = body surface or body length, y2 = one of the measurements analyzed, y1m, y2m = maximum values towards which y1 and y2 respectively tend, and c, b = constants. Only slight allometric differences in worms were observed despite the geographic distance between both Spanish and Bolivian sheep populations and the very high altitude of the Bolivian Altiplano.     

Development of Fasciola hepatica in Lymnaea columella infected with miracidia derived from cattle and marmoset infections

The development of Fasciola hepatica from two species of definitive hosts, i.e. cattle (Bos taurus) and a marmoset (Callithrix penicillata) in the snail Lymnaea columella was determined based on the production of rediae and cercariae and snail survival rate. More rediae and cercariae at 60-74 days post-infection were produced by snails infected by cattle-derived miracidia (cattle group) than by those infected by marmoset-derived miracidia (marmoset group). Among the L. columella parasitized by the marmoset group, the survival rate and the percentage of positive snails were higher than among those parasitized by the cattle group. Eggs of F. hepatica released in cattle faeces were significantly bigger than those released in marmoset faeces. Miracidia originating from parasites that completed their development in cattle were more efficient in infecting the intermediate host. These results suggest that vertebrate-host origin influences the eggs produced by the parasite and the infection rates in the snail host L. columella.