Experimental fascioliasis in Australia

Evaluation of an ELISA to assess the intensity of Fasciola hepatica infection in cattle

An elisa with a diagnostic sensitivity of 98 per cent and specificity of 96 per cent was evaluated as a means of assessing the intensity of Fasciola hepatica infection in cattle. A total of 294 blood samples were collected from infected cattle at a local abattoir, and the level of infection in each animal was assessed on the basis of the extent of liver pathology and the presence of flukes; 120 blood samples were also collected from uninfected cattle kept on a farm known to be free of F hepatica. The results indicated that there was a significant correlation (P<0.001) between the elisa values and the intensity of infection. Values between 15 and 28 per cent of a positive control sample indicated a low intensity of infection, values between 28 and 50 per cent indicated a medium intensity of infection and values above 50 per cent indicated a high intensity of infection.

Concurrent infections of Fasciola, Schistosoma and Amphistomum spp. in cattle from Kafue and Zambezi river basins of Zambia

This study investigated interactions among Fasciola gigantica, Schistosoma spp. and Amphistomum spp. concurrent natural infections in Zambian cattle, based on egg and worm counts. In the abattoir 315 cattle were screened for worms of F. gigantica in the liver, Schistosoma spp. in mesenteric veins and/or Amphistomum spp. in the rumen. One hundred and thirty-three (42.2%) of the abattoir-examined cattle harboured one, two or all three trematodes. Of 133 cattle, 50 were randomly selected for worm and egg counts. The mean numbers (+/- SD) of Amphistomum, Schistosoma and Fasciola were 622.08 (+/- 97.87), 33.68 (+/- 7.44) and 19.46 (+/- 4.58), respectively. A total of 32% harboured all the three trematodes, 66% had F. gigantica and Amphistomum spp. infections, 52% had Schistosoma spp. and Amphistomum spp. infections while 32% had F. gigantica and Schistosoma infections. A positive correlation (P = 0.014) was found between F. gigantica and Amphistomum worm burdens. There were no correlations between Amphistomum and Schistosoma worm burdens and between F. gigantica and Schistosoma worm burdens. It may be concluded that there is no significant cross-protection among these trematodes in cattle in endemic areas.

Oxidative Modifications of Rat Liver Cell Components During Fasciola hepatica Infection

The aim of this paper was to assess the influence of Fasciola hepatica infection on oxidative modifications of rat liver cell components such as proteins and lipids. Wistar rats were infected per os with 30 metacercariae of F. hepatica. Activities and concentrations of liver damage markers were determined in the 4th, 7th, and 10th week postinfection (wpi). A decrease in antioxidant capacity of the host liver, manifested by a decrease in total antioxidant status (TAS), was observed. Diminution of antioxidant abilities resulted in enhanced oxidative modifications of lipids and proteins. F. hepatica infection enhanced lipid peroxidation, which was visible in the statistically significant increase in the level of different lipid peroxidation products such as conjugated dienes (CDs), lipid hydroperoxides (LOOHs), malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE). The level of protein modification markers in the rat liver was also significantly changed and the most intensified changes were observed at seventh week postinfection. Concentration of carbonyl groups and dityrosine was significantly increased, whereas the level of tryptophan and sulfhydryl and amino groups was decreased. Changes in the antioxidant abilities of the liver and in the lipid and protein structure of the cell components resulted in destruction of the function of the liver. F. hepatica infection was accompanied by raising serum activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) as markers of liver damage. A significant decrease in lysosomal as well as in the total activity of cathepsin B during fasciolosis was also observed.

Host responses during experimental infection with Fasciola gigantica and Fasciola hepatica in Merino sheep II. Development of a predictive index for Fasciola gigantica worm burden

This study reports on the predictive relationship between serological, immunological and pathological responses following experimental inoculation with incremental doses of Fasciola gigantica in sheep. Fifty, 6-month-old, naive Merino wethers were allocated to one of 5 experimental groups, four of which received 50, 125, 225 and 400 metacercariae, respectively, whilst a 5th group acted as non-inoculated control. Strong individual correlations were observed between liver score, GLDH (glutamate dehydrogenase), GGT (gamma glutamyl transferase), CatL5 (cathepsin L5) antibody titre (IgG1, IgA), eosinophilia, and the total worm count or worm biomass. A combination of multiple indicator traits performed significantly better than any single indicator trait alone. The best predictive index accounted for up to 88% of observed worm burden (Wb) if information on inoculation dose was available. Without knowledge of inoculation dose, such as under field conditions, up to 67% of variation in worm burden could be predicted. In contrast, the best single predictor variable (liver damage score) accounted for up to 50% of worm burden, and in the absence of post-slaughter information, serum levels of anti-cathepsin IgA antibody titres accounted for 35% of predicted variation in worm burden. The utility of a predictive index under both field and experimental inoculation conditions is discussed.

Paramphistomum daubneyi: production dynamics and infectivity of metacercariae originating from snails dissected at regular intervals

Experimental infections of Galba truncatula with Paramphistomum daubneyi were carried out at 24 degrees C to study the dynamics of larval development in snails dissected at regular intervals and to determine if metacercarial production might be improved. When the shell height of snails (4, 5, 6 or 7 mm) at exposure increased (experiment A), the total number of metacercariae was significantly higher in the 6- and 7-mm snails than in the other two groups, and the differentiation period was shortened (the first cercariae encysted at day 35 post-exposure (p.e.) instead of day 40 in the 4- and 5-mm groups). When the number of miracidia (two, three or five) for each 6-mm high G. truncatula increased (experiment B), a significant decrease of snail survival at day 30 p.e., a significant augmentation of prevalence, and a significant increase of metacercarial production were noted. In the two- and three-miracidium groups, the number of metacercariae was close to that found in the 6-mm snails from experiment 1, whereas they showed slower growth from day 45 to day 65 in the five-miracidium group. In the two groups of lambs infected with metacercariae encysted at days 45 or 60 p.e., no difference in the numbers of adult worms was noted. In contrast, in the case of 35-day encysted larvae, the number of adult worms was clearly lower. Snail dissection allowed higher metacercarial production, a saving of 12-15 days at 24 degrees C to obtain these larvae, and a substantial decrease of their cost price for commercial production.

Development ofFasciola hepaticainLymnaea columellainfected with miracidia derived from cattle and marmoset infections

The development ofFasciola hepaticafrom two species of definitive hosts, i.e. cattle (Bos taurus) and a marmoset (Callithrix penicillata) in the snailLymnaea columellawas 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 theL. columellaparasitized by the marmoset group, the survival rate and the percentage of positive snails were higher than among those parasitized by the cattle group. Eggs ofF. hepaticareleased 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 hostL. columella.

Experimental infections with Fasciola in snails, mice and rabbits

Experimental infection trails of Lymnaea (cailliaudi) natalensis snails with miracidia of Fasciola hepatica revealed neither cercariae nor larval stages shed. Infection of white mice with metacercariae from field-collected snails proved to be negative for Fasciola eggs and immature juveniles or adults after 84 days post infection. The infection of eight rabbits (Oryctolagus cuniculus) has succeeded; two rabbits were infected, with a very low infection rate. Faeces of rabbits were negative for eggs. The worm burden was one and three worms from 40 fed metacercariae. The obtained fluke measures 23 mm in length by 4 mm in width. The tegument is covered with sharp-ending spines. The uterus contains few eggs. The intrauterine eggs measured 158 microm x 80 microm. According to the morphological characters of these flukes, they belong to F. gigantica.

Fasciola hepatica: an assessment on the vectorial capacity of Radix labiata and R. balthica commonly found in Belgium

A previous study conducted in Belgium revealed that genetic material of Fasciola sp. was present in snail species belonging to the genus Radix. Here, these snails were collected and identified by DNA-based techniques as Radix labiata and Radix balthica. These two species and Galba truncatula (the major intermediate host in Europe) were experimentally infected with Fasciola hepatica. The resulting metacercariae were fed to rats and the infection was monitored using several techniques. Microscopy revealed the presence of larval stages in 78.3, 45, and 6.25% of G. truncatula, R. labiata, and R. balthica snails, respectively. These results were confirmed by a PCR that amplifies a Fasciola sp. specific sequence. Furthermore, this PCR was found to be more sensitive than microscopic examination. R. labiata shed fewer metacercariae than G. truncatula but these were as infective to rats as those shed by G. truncatula. This study demonstrates that R. labiata may act as an incidental intermediate host for F. hepatica in Belgium.

Dynamics of Fasciola hepatica transmission in the Andean Patagonian valleys, Argentina

We described the transmission dynamics of Fasciola hepatica at its southern distribution range. Studies of prevalence and egg output in cattle and population dynamics and infection in snails were performed in a farm in the Andean Patagonian valleys, Argentina, between December 1998 and February 2002. Snail surveys were conducted from spring to autumn. Infection was diagnosed coprologically in the whole herd at the beginning and end of the study, and in a cohort of heifers at the beginning and end of 2001. A twice-a-year anthelmintic treatment was implemented in 1999. The relationship of the variables mentioned above with temperature and rainfall was determined. Lymnaea viatrix showed a life-span of about 15 months and an annual pattern of population dynamics. Specimens were frequently found in temporary environments and lagoons, and rarely in streams. Snail abundance and soil-water availability were directly related in temporary environments and inversely related in lagoons. Overall prevalence in L. viatrix was 0.67% (range: 0.9-14%) and infection was detected in summer and autumn. At the beginning of the study, calves were the least infected age group (15%). Prevalences and median egg counts in grazing animals were similar at the beginning (heifers: 81%, 3.3 epg; cows: 60%, 1.3 epg) and end of the study (heifers and cows: around 51%, 1 epg). Likewise, the prevalence in the cohort of heifers remained similar (around 40%) between surveys. Transmission to cattle was highly effective despite of the short activity period and the low infection rate of snails, and the regular anthelminthic treatment. There would be two seasonal transmission peaks, one in summer-autumn, when infected snails were present, and the other in early spring due to overwintering metacercariae. Some recommendations based on the climatic conditions of the region are provided to minimize snail infection and ultimately to reduce the incidence of fasciolosis in cattle.

Prevalence and intensity of infections in the lymnaeid snail Omphiscola glabra experimentally infected with Fasciola hepatica, Fascioloides magna and Paramphistomum daubneyi

Single and double infections of juvenile Omphiscola glabra (Gastropoda: Lymnaeidae) with Paramphistomum daubneyi and/or Fasciola hepatica were carried out to determine the redial burden and cercarial production in snails dissected at day 60 or at day 75 post-exposure (p.e.) in the laboratory at 20 degrees C. The results were compared with those obtained with single-miracidium infections by Fascioloides magna. Compared to F. hepatica, low values were noted at day 75 p.e. for the prevalence of snail infections with P. daubneyi (4.6-8.3% instead of 23.6-25.9%), the total number of free rediae (10.7-17.9 per snail instead of 26.3-34.7), and that of free cercariae (112.8-136.9 per snail instead of 177.8-248.5). Despite a greater number of free rediae at day 75 p.e. (36.2-45.6 per snail), the prevalences of snail infections with F. magna and cercarial production were similar to those noted for F. hepatica. The results concerning F. hepatica and P. daubneyi might partly be explained by a progressive adaptation of O. glabra to sustain the larval development of these digeneans over the years, as this snail is a natural intermediate host of F. hepatica and P. daubneyi in central France since 1995. Compared with the high number of fully-grown rediae of F. magna in O. glabra, cercarial production seemed limited and this might be explained by the presence of high numbers of rediae which reduced the avaibility of nutrients for cercarial differentiation within the snail.

Optimization of metacercarial production for three digenean species by the use of petri dishes for raising lettuce-fed Galba truncatula

Experimental infections of Galba truncatula with Fasciola hepatica, Fascioloides magna, or Paramphistomum daubneyi were carried out at 20 degrees C to determine if the use of 14-cm petri dishes for breeding lettuce-fed snails enhanced the characteristics of snail infections. Compared to infected snails raised in boxes up to day 30 post-exposure and later in individual 35-mm dishes, the survival of G. truncatula kept in 14-cm dishes and the shell height of cercariae-shedding snails during the first 45 days were higher, whatever the digenean species is. The consequence of such enhanced characteristics was a greater production of metacercariae in the case of F. hepatica (1.7 to 5.6 times higher) and P. daubneyi (2.3 times). In contrast, metacercariae of F. magna were few in number, whatever the method of snail breeding is, and this might be explained by a still incomplete adaptation between the parasite of Czech origin and the French population of G. truncatula. The use of these 14-cm dishes reduced the time necessary for snail maintenance and metacercaria collection, thus allowing a decrease in the cost price of these larvae for commercial production.

Phenotypic analysis of adults and eggs of Fasciola hepatica by computer image analysis system

Knowledge of the morphological phenotypes of the liver fluke Fasciola hepatica (Trematoda: Digenea) is analysed. The influence of parasite age on its dimensions, the adult fluke growth model, variation in a biometric variable versus time, and variation in a biometric variable versus another biometric variable (allometric model) are revised. The most useful allometric model appears to be (y2m]#x2212;y2)/y2=c [(y1m−y1)/y1]b, where y1=body area or body length, y2=one of the measurements analysed, y1m, y2m=maximum values towards which y1 and y2, respectively, tend, and c, b=constants. A method based on material standardization, the measurement proposal and allometric analysis is detailed. A computer image analysis system (CIAS), which includes a colour video-camera connected to a stereomicroscope (for adult studies) and a microscope (for egg studies), facilitates the processing of digital imaging. Examples of its application for the analysis of the influence of different factors on the liver fluke phenotype are shown using material from the Northern Bolivian Altiplano, where human and domestic animal fascioliasis is caused by F. hepatica only. Comparisons between the development of livestock fluke populations from highlands and lowlands are discussed and the relationships between host species and liver fluke morphometric patterns is analysed.

Larval productivity ofFasciola giganticain two lymnaeid snails

Two groups ofGalba truncatulaand two groups ofLymnaea natalensiswere experimentally infected withFasciola giganticato determine if snail species had an influence on the redial burden and cercarial shedding of this trematode when snails of both species were infected with the same isolate of miracidia. In the two groups used for the study of redial burden, the total number of free rediae was significantly higher at day 49 post-exposure inL. natalensisthan inG. truncatula. In the groups used for cercarial shedding, the life-span of cercaria-shedding snails and those of infected snails which died without cercarial emission, and the duration of the prepatent period were significantly longer inL. natalensisthan those noted inG. truncatula. However, the mean numbers of shed cercariae did not significantly differ and showed no differences in their daily distribution throughout the shedding period. These results demonstrate thatG. truncatulamight be the principal intermediate host ofF. giganticain Egypt, at least in the areas where this lymnaeid species lives.

Prevalence of Fasciola hepatica (ELISA and fecal analysis) in ruminants from a semi-desert area in the northwest of Mexico

The aim of the present study was to estimate the prevalence of Fasciola hepatica in cattle, goats and sheep from the municipalities of Guaymas and Cajeme, Sonora State, Mexico using the indirect ELISA and Benedeck's sedimentation tests. A total of 2,936 serum and fecal samples from 1,346 bovines, 1,199 goats and 381 sheep were analyzed. Other parameters such as breed and age were also taken into consideration. The results indicated a moderate percentage of prevalence for fasciolosis in these municipalities. In bovines, a prevalence of 11.4 +/- 0.9 was found using the sedimentation test and 24.4 +/- 1.2 for the indirect ELISA. In goats, a prevalence of 24.5 +/- 1.2 was found for the fecal analysis and 43 +/- 1.5 for the indirect ELISA. In sheep, the prevalence for both tests was 19.4 +/- 2.0 and 30.6 +/- 2.7, respectively. Results showed a greater proportion of positive animals when the ELISA test was used than when the Benedeck's sedimentation test was applied. Moderate agreement was observed between both laboratory tests for the three species of ruminants included in the study (Cohen's kappa, K; cattle K=0.527, goats K=0.541 and sheep K=0.539).

Exposure to Fasciola hepatica miracidia increases the sensitivity of Lymnaea (Fossaria) humilis to high and low pH

Humidity and temperature have been considered important factors affecting the infectivity of Fasciola hepatica to its molluscan host. One hundred and thirty laboratory-reared Lymnaea humilis were exposed for 4 hr to the miracidia of F. hepatica over a pH range from 4.0 to 10.0, and their rates of survival were compared with 130 similarly treated but unexposed control snails. All control snails died within 24 hr at pH 4.0, but they showed better survival at pH 5.0-10.0. Their sensitivity to solutions with high and low pH, however, was increased if kept in the presence of F. hepatica miracidia. Snails exposed at pH 5.0 died within 24 hr, whereas most other pHs also affected survival such that by day 18 only those snails exposed at pH 7.2 remained alive. The increased sensitivity of the snails to pH could be explained by a damage-mediated release of parasite enzymes, because infectivity was highest at pHs associated with the lowest host mortality.

Crowding effect on adult growth, pre-patent period and egg shedding of Fasciola hepatica

Fascioliasis pathogenesis depends on fluke burden. In human hyperendemic zones, individual infection intensities reach very high levels and the majority of infected subjects should be in the advanced chronic phase. The rat model offers a useful approach for pathological research in the advanced chronic period. The influence of infection intensity per rat on fluke development, pre-patent period and egg shedding (eggs/g faeces/worm) was analysed in 3 groups (I: 1–3 worms/rat; II: 4–6; III: 7–9). Ontogenetic trajectories of fluke body measures followed a logistic model. Results showed that when the burden increases, the maximum values of fluke measures decrease. The crowding effect is manifest when fluke measures approximate their maximums in the advanced chronic stage. The pre-patent period and egg production decrease when the burden increases. This means that measurements of eggs per gramme of faeces tend to underestimate the fluke burden. The present study demonstrates how to quantify the fascioliasis experimental rat model crowding effect on adult growth, pre-patent period and egg production. This quantification may be of great interest in epidemiological studies and in experimental research on the in vivo actions of different anthelminthic drugs and vaccines, pathology, immunology and resistance studies.

The effect of temperature and humidity on longevity of metacercariae of Fasciola gigantica

Studies were undertaken on the viability of the metacercariae of Fasciola gigantica when stored in water at 13 degrees C for periods up to 23 weeks, exposed to the sunlight for up to 8 h or stored at a range of temperatures and humidities for up to 10 weeks. Excysted metacercariae were catergorized microscopically as viable (motile and undamaged), dubious (not motile and undamaged) or dead (visible necrosis). The infectivity of viable and dubious metacercariae and unselected reference metacercariae held in water at 7 degrees C for 20 days or longer was assessed by comparing numbers of flukes recovered from infected Merino sheep. Mean recovery rates were 54.6%, 7.2% and 37.2%, respectively, for viable, dubious and unselected metacercariae. Metacercariae immersed in water remained viable longer than those allowed to desiccate. Viability was promoted by decreasing temperature and increasing humidity. Exposure to direct sunlight killed metacercariae within 8 h. Results indicated that in lowland Indonesian irrigated rice paddies, metacercariae immersed in water are likely to survive for less than 5 weeks while those that become desiccated will survive less than 2 weeks. This information, together with the option of exposing fresh rice stalks to direct sunlight before feeding them to livestock, can assist farmers in reducing infection with F gigantica.

Serum antibody isotype responses of Fasciola-infected sheep and cattle to excretory and secretory products of Fasciola species

This study investigated the immunoglobulin isotype responses of sheep and cattle chronically infected with Fasciola hepatica and Fasciola gigantica to adult F. hepatica excretory/secretory products (Fh-ES) or F. gigantica excretory/secretory products (Fg-ES), respectively. An antibody enzyme-linked immunosorbent assay (Ab-ELISA) was used to determine serum antibody (total Ig, IgG(1), IgM, IgG(2) and IgA) responses. At necropsy, the mean number of flukes recovered was lower in cattle than in sheep. All F. hepatica and F. gigantica infected sheep and cattle showed an increased total Ig levels from 3 to 4 weeks post-infection (wpi). Among isotypes IgG(1) was most dominant while IgM was the earliest (2 wpi) to be detected in both sheep and cattle infected with both F. hepatica and F. gigantica animals. IgG(2) response was early (2 wpi) in sheep infected by F. hepatica but there was no response in sheep infected with F. gigantica. There was a late and strong IgG(2) response in cattle infected with both flukes. The IgA isotype showed an early and a clear biphasic response in sheep with F. hepatica but was less pronounced in F. gigantica infected sheep. While IgA response to Fh-ES was noticed 5 wpi in F. hepatica infected cattle, it appeared much later (21 wpi) in those infected with F. gigantica. The dominance of IgG(1) isotype in infected sheep and cattle suggest an associated Th2 response. This early response to adult Fasciola spp. ES antigen suggests an early exposure to the antigen presumably through the cross-reacting ES products of juvenile flukes. There is clearly difference in IgG(2) isotype response in cattle (resistant) compared to sheep (susceptible). The late IgG(2) response in cattle may suggest late Th1 involvement in bovine cellular responses to adult Fh-ES/Fg-ES.

Fasciola hepatica: Effects on the antioxidative properties and lipid peroxidation of rat serum

Fasciola hepatica infection is accompanied by increased formation of reactive oxygen species. The aim of this study was to analyze antioxidative properties of rat serum in the course of fasciolosis. Wistar rats were infected per os with 30 metacercariae of F. hepatica. Activities of antioxidant enzymes and concentrations of non-enzymatic antioxidants in serum were determined at 4, 7, and 10 weeks post-infection (wpi). Activity of superoxide dismutase (Cu, Zn-SOD) significantly decreased (by 35% during the migratory phase, by 40 and 23% at 7 and 10 wpi, respectively), while glutathione reductase activity significantly increased (by 62, 65, and 41%, at 4, 7, and 10 wpi, respectively). No significant changes were found in the activity of glutathione peroxidase. Significant decreases in concentrations of reduced glutathione, vitamins C, E, and A were observed, particularly during the migratory phase of fasciolosis (at 4 wpi). These changes were accompanied by enhancement of lipid peroxidation processes as evidenced by increased levels of malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE). Concentrations of MDA and 4-HNE at 4 wpi increased by 38% and by 59%. MDA increased by 51% at 7 wpi and by 79% at 10 wpi, while 4-HNE increased by 87 and 118%, respectively. The results indicate that fasciolosis is associated with enhanced oxidative reactions and reduced antioxidant defense capability of rat serum.

The presence of uninfected Omphiscola glabra in a breeding of infected Galba truncatula enhanced the characteristics of snail infections with Fasciola hepatica

Experimental infections of Galba truncatula with Fasciola hepatica were carried out under laboratory conditions to determine if the presence of another lymnaeid, Omphiscola glabra, during snail breeding had an indirect effect on the growth of G. truncatula and to analyse consequences on cercarial production. When the two lymnaeids are raised together, the survival of G. truncatula at day 30 post-exposure (PE), the prevalence of snail infections, and the shell height of cercariae-shedding snails at day 45 PE were significantly higher. By contrast, the other parameters characterizing snail infections only showed insignificant variations. The origin of O. glabra (living in a snail community, or monospecific population) used for the breeding of G. truncatula did not have a significant effect on the values of each parameter. Even if variations in the mean numbers of metacercariae were insignificant, the greater survival of G. truncatula at day 30 PE and the higher numbers of cercariae-shedding snails in the groups living with O. glabra allowed to obtain a higher total number of larvae than in alone-raised groups of G. truncatula.

Reviewing lymnaeid vectors of fascioliasis by ribosomal DNA sequence analyses

Snails of the family Lymnaeidae are of great parasitological importance due to the numerous helminth species they transmit, mainly trematodiases (such as fascioliasis) of considerable medical and veterinary impact. The present knowledge of the genetics and host-parasite relationships of this gastropod group is far from adequate. Fascioliasis is caused by two species, Fasciola hepatica and F. gigantica, which, as in the case of other trematodes, show a marked snail host specificity. Many lymnaeid species involved in fascioliasis transmission still show a confused systematic-taxonomic status. The need for tools to distinguish and characterize species and populations of lymnaeids is evident and the present review concerns new molecular tools developed in recent years using nuclear ribosomal DNA sequences. The small subunit or 18S gene and the internal transcribed spacers ITS-2 and ITS-1 are analysed and evaluated as markers for taxon differentiation and relationships within the Lymnaeidae from genus and species levels to subspecies and population levels. rDNA sequence differences and genetic distances, and their value for reconstructing phylogenetic trees using different methods are considered. Nuclear rDNA sequences are appropriate tools on which to base a review of the systematics and taxonomy of the family Lymnaeidae, without excluding other valuable snail characteristics already available. A reconstruction of the lymnaeid system towards a more natural classification will undoubtedly be helpful in understanding parasite transmission and epidemiological features as well the dispersion of an emerging-reemerging disease such as fascioliasis. Nomenclature for nuclear rDNA genotyping in lymnaeids includes the main rDNA sequence regions able to furnish important information on interspecific differentiation and grouping as well as intraspecific variability of lymnaeid species. The composite haplotype code includes the rDNA markers arranged in order according to their well-known usefulness, in its turn related to their respective, more or less rapid evolutionary ratios, to distinguish between different taxonomic levels, from supraspecific taxa to the species level and up to the population level.

A retrospective study on the metacercarial production of Fasciola hepatica from experimentally infected Galba truncatula in central France

A retrospective study of the experiments performed during the past 15 years on infections of Galba truncatula with Fasciola hepatica was carried out to determine what susceptible populations of snails might be used for the commercial production of metacercariae, and to examine this metacercarial production in relation to the characteristics of snail infections. Of the four groups of snail populations studied, the ablest snails to sustain a complete larval development of F. hepatica originated from populations living on siliceous soils at 600 m and more in altitude. In contrast, snail populations living along river banks on siliceous soils were inappropriate due to the poor characteristics of snail infections (high snail mortality, low prevalence of snail infections, and low number of cercariae produced). Except for these last populations, 86-87% of cercaria-shedding (CS) snails in the other populations shed less than 300 cercariae, even if a maximum of 1,772 cercariae were obtained from a single snail. The date of the first cercarial shedding at 20 degrees C began during week 7 or 8 PE for 80.1-83.5% of CS snails. Most metacercariae (82.0-85.9% of the total production) were recorded during the first 10 days of the patent period. In these conditions, the authors collected metacercarial production up to the beginning of week 10 PE (20 degrees C) and did not use snails that shed their cercariae during the following weeks due to too low numbers of parasites. This method allows to have a continuous production of metacercariae over time by using successive groups of infected snails, each being separated from the other by a fortnight's time.

Bayesian hierarchical modelling to enhance the epidemiological value of abattoir surveys for bovine fasciolosis

Four classes of Bayesian hierarchical models were evaluated using an historical dataset from an abattoir survey for fasciolosis conducted in Victoria, Australia. The purpose of this analysis was to identify areas of high prevalence and to explain these in terms of environmental covariates. The simplest of the Bayesian models, with a single random effect, validated the use of smoothed maps for cartographic display when the sample sizes vary. The model was then extended to partition the random effect into spatially structured and unstructured components, thus allowing for spatial autocorrelation. Rainfall, irrigation, temperature-adjusted rainfall and a remotely sensed surrogate for rainfall, the normalised difference vegetation index (NDVI), were then introduced into the models as explanatory variables. The variable that best explained the observed distribution was irrigation. Associations between prevalence and both rainfall and NDVI that were significant in fixed effects models were shown to be due to spatial confounding. Nevertheless, provided they are used cautiously, confounded variables may be valid predictors for the prevalence of disease.

Chemoprophylaxis of fascioliasis with triclabendazole

In a field experiment, moderate to heavy natural concomitant infections with immature and mature Fasciola hepatica were treated with triclahendazole at a dose rate of 10 mg/kg and an efficiency of 99.8% was achieved. Subsequent treatments of all susceptible farm animals at the same dose rate at intervals of eight to eleven weeks were carried out for 14 months; no patent infections could be detected in sheep and cattle during the whole period. Evidence is presented that pasture contamination with liver fluke was reduced to a negligible level for a further 12 months after the final treatment. It is suggested that, if regular treatments with triclabendazole are given within the pre-patent period of Fasciola hepatica infection for the whole season, the infection can be eradicated or reduced to such a low level that control of the disease could be maintained with less frequent strategic drenching for a considerable period.

Antioxidant potential of rat liver in experimental infection with Fasciola hepatica

The aim of this paper is to assess the antioxidant properties of rat liver in the course of acute and chronic fasciolosis. Wistar rats were infected per os with 30 metacercariae of Fasciola hepatica. Liver activities of antioxidant enzymes and concentrations of non-enzymatic antioxidants were determined at 4, 7, and 10 weeks post-infection. Activities of superoxide dismutase (Cu,Zn-SOD), glutathione peroxidase (GSH-Px), and glutathione reductase (GSSG-R) were decreased, catalase (CAT) activity was increased and non-enzymatic antioxidant concentrations (reduced glutathione, vitamins C, E and A) were reduced simultaneously with enhancement of lipid peroxidation processes as evidenced by increased levels of malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE). Changes in the antioxidant abilities of the liver and in the phospholipid structure of the cell membrane were accompanied by rising activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) as markers of liver damage.

Fasciola hepatica: an unusual case of adaptation to a Moroccan population of Galba truncatula

Parent snails, F1, and F2, originating from a Moroccan population of Galba truncatula, were experimentally subjected to sympatric miracidia of Fasciola hepatica at 20 degrees C to determine the mode of adaptation of this parasite to the local intermediate host via the study of redial burdens and by following cercarial shedding. In spite of an increase in the global prevalences of infections, the frequencies recorded for immature or mature infections in dissected snails did not show any significant variations from parents to F2. If the redial burdens in mature infections were mainly composed of first-generation rediae in parent snails, the numbers of rediae belonging to subsequent generations significantly increased in the F1 and F2 generations. In mature infections, the lengths of first-generation rediae and their contents significantly decreased from parent snails to F2. Conversely, in the first redial cohort of the second generation (R2a rediae), only the intraredial contents increased significantly with snail generation. In mature infections, daughter redia production was ensured by all mother rediae of the first generation in parent snails, whereas it was progressively effected by the first mother redia in the F1 and F2 infections. The numbers of cercariae shed by snails increased significantly from parents to F2. If the cercariae produced by first-generation rediae decreased with snail generation, an inverse finding was noted in the case of R2a rediae. We suggest that snails impose a bottleneck on the development of the first mother redia, so that other mother rediae of the first generation react with greater growth (until 3.9 mm in parent snails), an important daughter redia production and a high cercarial production. As the first mother redia remained alive until day 49 post-exposure but without growth after week 2, this mode of development must be considered as a new developmental pattern of redial generations, and it is useful to determine its frequency in snails, as it has never been found in naturally or experimentally infected snails in central France.

Fasciola hepatica: epidemiological surveillance of natural watercress beds in central France

A total of 59 natural watercress beds in the Limousin region (central France) was surveyed over a 15-year period (1990-2004) to detect the contamination of watercress by the metacercariae of Fasciola hepatica and to determine the presence of larval forms in the two species of lymnaeids which live in these waterholes in June and July. The number of beds contaminated with F. hepatica metacercariae varied over the years, and the burden of the larvae on plants was low: a mean of 2.6-6.3 per bed. The same variability was also noted for natural infections of Galba truncatula with F. hepatica, as the annual prevalences ranged from 1.2% to 2.4%. Natural infections of Omphiscola glabra with F. hepatica were only detected from 1996 and the annual prevalences subsequently increased up to 1.4-1.8% between 2001 and 2004. However, for both lymnaeids, the variations in these prevalences with year were insignificant. The contamination of these beds with F. hepatica over the past 15 years was similar to that recorded in the same sites between 1970 and 1986. The main changes were the appearance of another digenea, Paramphistomum daubneyi, in the beds, and the possibility for O. glabra to naturally sustain the larval development of F. hepatica.

The use of tetraphyll as food for snails increases the intensity of cercarial shedding in Galba truncatula infected with Fasciola hepatica

Experimental infections of Galba truncatula with Fasciola hepatica were carried out under laboratory conditions to determine why the use of Tetraphyll, when provided every 3 days as food for snails, stimulated the intensity of cercarial shedding. In snails raised on cos lettuce and Tetraphyll, the number of metacercariae was significantly higher than that recorded in controls on lettuce only. In the former group, numerous metacercariae were counted on day 1 of every 3-day period (when snails fed on Tetraphyll), while the numbers of these larvae strongly decreased on day 2 and were very low on day 3. The repetition of this experiment using microalgae or modified Boray's diet every 3 days as food for snails gave the same results. However, the number of metacercariae recorded on day 1 of every 3-day period was significantly higher in snails raised on lettuce and Tetraphyll than in those reared on lettuce and algae (or Boray's diet). According to the authors, the first contact of an infected snail with Tetraphyll induces a faster differentiation of cercariae within the rediae and the accumulation of many free cercariae in the snail's hemocoel, so that a second contact of the snail with this food 3 days after allows free cercariae to complete their glycogen and fat reserves and to rapidly exit from the snail. However, a temporary immobilization of the infected snail by Tetraphyll, or rather its degradation products, and a massed exit of cercariae cannot be excluded.

A RECOMBINANT ANTIGEN RECOGNIZED BY FASCIOLA HEPATICA–INFECTED HOSTS

This work reports the detection of specific immunoglobulins (Ig) against rFh8, a recombinant Fasciola hepatica adult worm excretion-secretion antigen, in sera from experimentally (rabbit, Wistar rat, cattle, and sheep), or naturally (human) infected hosts. In the case of laboratory experimental models the study revealed significant differences between rabbits, which recognized the recombinant antigen all along the infection, and Wistar rats, which showed high anti-rFh8 Ig levels only for a short period of the infection. Available sera from experimentally infected cattle and sheep, as well as sera from naturally F. hepatica-infected humans, also contained significant levels of Ig against rFh8, suggesting that Fh8 was produced by F. hepatica at a very early stage of infection in all hosts so far analyzed and that the rFh8 antigen could be used as a tool for the diagnosis of F. hepatica infections.

Herd-level seroprevalence of fasciolosis in cattle in north central Portugal

An epidemiological study of Fasciola hepatica in cattle was implemented in the north central region of Portugal. Both an enzyme-linked immunosorbent assay and an egg shedding quantification technique were used in the follow-up of seven herds. Two of these herds were negative and the other five were positive for F. hepatica. A herd cut-off of value of 0.425 optical density was calculated and herd sensitivity (HSe) and herd specificity (HSp) were defined. Three seroprevalence studies were also implemented in the region with stratification by county sub-regions for a period of 18 months. Overall mean herd prevalence in Vagos of 11, 23 and 48% was progressively found for the three studies, respectively.

Immunology of the host–parasite relationship in fasciolosis (Fasciola hepaticaandFasciola gigantica)

The protective resolution of liver fluke (Fasciola hepatica and Fasciola gigantica) infection is a dynamic interplay between the host's effector responses and the parasite's defence and immunomodulatory systems. The evidence suggests that the juvenile or immature parasite is the target of protective host immune responses but the effector mechanisms employed vary between hosts. Moreover, F. hepatica and F. gigantica differ in their susceptibility to these killing mechanisms. In the rat, in vitro killing of juvenile F. hepatica involves an antibody-dependent cell cytotoxicity mediated by nitric oxide produced by activated monocytes and (or) macrophages. However, monocytes and (or) macrophages from Indonesian sheep do not produce nitric oxide yet can effectively kill juvenile F. gigantica in vitro and in vivo by a mechanism that is ineffective against F. hepatica. These data show that disease progression or resolution in fasciolosis is determined both by biochemical differences between Fasciola species and by host-dependent factors. Understanding the genetic basis for these differences is a key question for the future. Fasciola hepatica and F. gigantica actively modulate the host immune response, downregulating type 1 responses during infection. It is important to determine whether such modulation of the immune response by Fasciola spp. directly leads to enhanced parasite survival in the various hosts.

The experimental production of Fasciola hepatica metacercariae from three aquatic populations of Galba truncatula

Laboratory investigations on three aquatic populations of Galba truncatula, originating from the Peruvian Altiplano and French Massif Central, were carried out during three successive snail generations to determine if these populations might be successfully used for the metacercarial production of Fasciola hepatica under experimental conditions. High numbers of surviving snails at day 30 post-exposure (>70%), high prevalences of F. hepatica infections (>60%), and prolonged productions of cercariae for a mean period of 35 to 47 days were observed in the three populations, whatever the snail generation. In the Peruvian population, metacercariae of F. hepatica significantly decreased in numbers from a mean of 251 in the parent snails to 124 per snail in the F2 generation, whereas no significant variation was observed in the two French populations. As these aquatic snails rarely emerged out of water, the use of these populations for the commercial production of F. hepatica metacercariae was of great interest, because the daily time spent watching the breeding boxes of snails was clearly shorter, thereby reducing the cost of producing metacercariae compared with using amphibious snails reared with romaine lettuce.

Fasciola gigantica: larval productivity of three different miracidial isolates in the snail Lymnaea truncatula

Bimiracidial infections of Lymnaea truncatula with three isolates of Fasciola gigantica, originating from China, Egypt and Madagascar, were carried out to determine the effect of geographic origin of the parasite on the larval productivity of redial generations. The prevalences of experimental infections in snails exposed to strains from Madagascar, China and Egypt were 20.8%, 60.0% and 80.0%, respectively. At day 49 post-exposure (p.e.), the total number of free rediae in snails infected with the Egyptian isolate was significantly higher than that recorded in the Madagascan group. On the other hand, at day 49 p.e., the majority of cercariae in the Chinese and Egyptian groups were produced by R2a rediae (70.6% and 66.6% of cercariae produced by all live rediae), while, in the Madagascan group, the cercariae were produced mainly by the first redial generation. Snails infected with the Egyptian isolate of miracidia developed more live rediae and, consequently, could produce a higher number of cercariae. As a result, L. truncatula snails were highly adapted to infections with the Egyptian and Chinese isolates of F. gigantica.

Pre-exposure of cattle to drug-abbreviated Fasciola hepatica infections: the effect upon subsequent challenge infection and the early immune response

In this study we examined whether juvenile liver flukes are capable of stimulating protective immune responses in cattle. Four experimental groups of cattle were studied as follows: group A, a positive control, received a primary infection on day 0 and a secondary infection 28 days later; group B also received two infections but the primary infection was terminated by drug treatment on day 5; group C, received infections on days 0, 5 and 10 which were terminated by drug treatments on days 1, 6 and 11 and then a secondary infection on day 28; group D received an infection only on day 28. Juvenile flukes appear to induce protective responses because: (a) group B animals had significantly lower levels of gamma-GT (P<0.05) than group D; (b) both groups B and C exhibited lower parenchymal phase GLDH levels (P=0.006 and 0.041, respectively); and (c) both groups B and C had lower secondary phase eosinophilia (P=0.002 and 0.02, respectively) than those in group D. Sera taken from groups A-C contained antibodies reacting to a variety of proteins in adult fluke somatic antigen and excretory-secretory preparations, particularly to proteins of 52-60, 68-72 and 82-96 kDa. After secondary challenge the antibody responses of group A to these proteins declined while reactivity to proteins of 28-30 kDa increased. Antibody responses to the 28-30 kDa proteins were not detected in groups B-D until 3 weeks later than those observed in group A. Antibody responses to Fasciola hepatica cathepsin L proteases, which are known to induce protection, were monophasic, of the IgG1 isotype only and were not observed prior to secondary challenge in any of the four groups. In contrast, the response to another protective antigen fraction, a high molecular sized haem protein, was of a mixed IgG1/IgG2 nature and was detected within 14 days of primary infection. However, no significant difference in antibody titres to either protein preparation was observed after the secondary infection when groups B and C were compared to group D.

Cloning, heterologous expression in Escherichia coli and characterization of a protein disulfide isomerase from Fasciola hepatica

A Fasciola hepatica cDNA clone of 1752 bp was isolated from an adult worm cDNA expression library by immunological screening using a rabbit serum against the excretory-secretory antigens. The nucleotide sequence of the cDNA revealed the presence of an open reading frame of 489 codons which encoded a 55 kDa polypeptide, showing a high degree of homology to protein disulfide isomerases. This putative antioxidant protein cDNA was expressed in Escherichia coli as a GST fusion protein. The cleaved recombinant protein was shown to be biologically active in vitro by mediating the oxidative refolding of reduced RNase. Immunoblotting studies using a specific antiserum raised against the recombinant protein showed the presence of a polypeptide of similar molecular mass in the excretory-secretory extract of the adult parasite. The extracellular location of this protein was also supported by the specific immune responses found against this protein in F. hepatica experimentally infected rabbits.

Evaluation of a simple sedimentation method (modified McMaster) for diagnosis of bovine fascioliosis

A coprological sedimentation method is evaluated for quantification of egg shedding in bovine faeces. Through the inclusion of different number of Fasciola hepatica eggs in negative faeces, egg recovery rate and the sensitivity of the method were determined. The mean egg recovery rate of the technique was 76.72+/-15.42%. The sensitivity of the method was 33.3% whenever eggs/g of faeces (EPG) are less than 1.5 and 100% for higher values. To improve the diagnostic accuracy with this technique, it is advisable to increase the sample from 10 to 30g of faeces when manipulating low egg shedding, which allowed for a sensitivity of 83.3%. Regression equations were calculated to quantify the relationship between the number of recovered and incorporated eggs.

Patterns in size and shedding of Fasciola hepatica eggs by naturally and experimentally infected murid rodents

Using samples collected on the island of Corsica, a comparative study was done of the morphometry of Fasciola hepatica eggs shed by cattle and by naturally and experimentally infected murid rodents (wild Mus musculus and Rattus rattus and Rattus norvegicus Wistar laboratory strain). Eggs shed by murids are smaller in size than those shed by naturally infected cattle. A second study analyzed the number of F. hepatica eggs shed in murid feces at different time intervals, i.e., months, days, and 6-hr periods, by the Kato-Katz technique. Both experimentally and naturally infected black rats (R. rattus) were used, and Wistar rats were experimentally infected and included for comparison. The present studies prove that black rats R. rattus are able to shed eggs independently from the liver fluke isolate and that egg shedding occurs throughout the life of this host species, uninterrupted during all the months analyzed in a 2-yr period. Moreover, the results suggest that this shedding is continuous, with eggs appearing in the feces daily. The results on egg shedding by wild black rats R. rattus reach their maximum shedding in spring and autumn and a maximum during twilight hr. These chronobiological patterns appear to favor parasite transmission, both seasonally and daily.

Relationships between host species and morphometric patterns in Fasciola hepatica adults and eggs from the northern Bolivian Altiplano hyperendemic region

The highest prevalences and intensities of human fasciolosis by Fasciola hepatica are found in the northern Bolivian Altiplano, where sheep and cattle are the main reservoir host species and pigs and donkeys the secondary ones. Morphometric comparisons of many linear measurements, areas and ratios of F. hepatica adults (from sheep, cattle and pigs) and eggs (from sheep, cattle, pigs and donkeys) in natural liver fluke populations of the Bolivian Altiplano, as well as of F. hepatica adults and eggs experimentally obtained in Wistar rats infected with Altiplanic sheep, cattle and pig isolates, were made using computer image analysis and an allometric model. Although morphometric values of adult flukes from natural populations of sheep, cattle, and pigs showed great overlap, there were clear differences in allometric growth. The allometries analyzed were: body area (BA) versus body length (BL), BA versus body width (BW), BA versus perimeter (Pe), BA versus distance between posterior end of body and ventral sucker (P-VS), BL versus BW, BL versus Pe, and BL versus P-VS. These allometries show a good fit in the seven pairs of variables in all the populations examined. Comparative statistical analysis of the allometries shows that fluke adult populations from sheep, cattle and pigs significantly differ in BL versus BW and BL versus P-VS functions. Statistical analysis of F. hepatica egg size shows characteristic morphometric traits in each definitive host species. In experimentally infected rats, fluke adult allometry and egg morphometry do not vary depending on the Altiplanic definitive host species isolate. Our study reveals that the definitive host species decisively influences the size of F. hepatica adults and eggs, and these influences do not persist in a rodent definitive host model.

European Lymnaeidae (Mollusca: Gastropoda), intermediate hosts of trematodiases, based on nuclear ribosomal DNA ITS-2 sequences

Freshwater snails of the family Lymnaeidae are of a great parasitological importance because of the very numerous helminth species they transmit, mainly trematodiases of large medical and veterinary impact. The present knowledge on the genetics of lymnaeids and on their parasite-host inter-relationships is far from being sufficient. The family is immersed in a systematic-taxonomic confusion. The necessity for a tool which enables species distinction and population characterization is evident. This paper aims to review the European Lymnaeidae basing on the second internal transcribed spacer ITS-2 of the nuclear ribosomal DNA. The ITS-2 sequences of 66 populations of 13 European and 1 North American lymnaeid species, including the five generic (or subgeneric) taxa Lymnaea sensu stricto, Stagnicola, Omphiscola, Radix and Galba, have been obtained. The ITS-2 proves to be a useful marker for resolving supraspecific, specific and population relationships in Lymnaeidae. Three different groupings according to their ITS-2 length could be distinguished: Radix and Galba may be considered the oldest taxa (370-406 bp lengths), and Lymnaea s. str., European Stagnicola and Omphiscola (468-491 bp lengths) the most recent, American Stagnicola and Hinkleyia being intermediate (434-450 bp lengths). This hypothesis agrees with the phylogeny of lymnaeids based on palaeontological data, chromosome numbers and radular dentition. ITS-2 sequences present a conserved central region flanked by two variable lateral regions corresponding to the 5' and 3' ends. The number of repeats of two microsatellites found in this conserved central region allows to differentiate Radix from all other lymnaeids. Phylogenetic trees showed four clades: (A) Lymnaea s. str., European Stagnicola and Omphiscola; (B) Radix species; (C) Galba truncatula; and (D) North American stagnicolines. ITS-2 results suggest that retaining Stagnicola as a subgenus of Lymnaea may be the most appropriate and that genus status for Omphiscola is justified. Radix shows a complexity suggesting different evolutionary lines, whereas G. truncatula appears to be very homogeneous. North American and European stagnicolines do not belong to the same supraspecific taxon; the genus Hinkleyia may be used for the American stagnicolines. Genetic distances and sequence differences allowed us to distinguish the upper limit to be expected within a single species and to how different sister species may be. S. palustris, S. fuscus and S. corvus proved to be valid species, but S. turricula may not be considered a species independent from S. palustris. Marked nucleotide divergences and genetic distances detected between different S. fuscus populations may be interpreted as a process of geographic differentiation developping in the present. Among Radix, six valid species could be distinguished: R. auricularia, R. ampla, R. peregra (=R. ovata;=R. balthica), R. labiata, R. lagotis and Radix sp. The information which the ITS-2 marker furnishes is of applied interest concerning the molluscan host specificity of the different trematode species. The phylogenetic trees inferred from the ITS-2 sequences are able to differentiate between lymnaeids transmitting and those non-transmitting fasciolids, as well as between those transmitting F. hepatica and those transmitting F. gigantica. The Fasciola specificity is linked to the two oldest genera which moreover cluster together in the phylogenetic trees, suggesting an origin of the Fasciola ancestors related to the origin of this branch. European Trichobilharzia species causing human dermatitis are transmitted only by lymnaeids of the Radix and Lymnaea s. str.-Stagnicola groups. Results suggest the convenience of reinvestigating compatibility differences after accurate lymnaeid species classification by ITS-2 sequencing. Similarly, ITS-2 sequencing would allow a step forward in the appropriate rearrangement of the actual systematic confusion among echinostomatids.

Vaccination of sheep against Fasciola hepatica with homologous fatty acid binding proteins

The current study was designed to test the immunoprophylactic properties of native (nFh12) and recombinant (rFh15) antigens from Fasciola hepatica in sheep subsequently infected with the fluke. Thirty lambs were divided into six groups according to various patterns of immunisation and times of infection and necropsy. The antigens were emulsified in Freund's adjuvant. Levels of specific anti-nFh12 and anti-rFh15 antibodies rose rapidly by 2 weeks after the first immunisation and were always significantly higher in immunised-infected sheep than in control-infected sheep. On completion of the trial there was no difference in fluke burden between groups vaccinated with either of the antigens and non-immunised controls. However, worm size and faecal egg counts were significantly diminished in the sheep vaccinated with either of the antigens, suggesting an anti-fecundity effect. This is the first report of experimental vaccination of sheep against F. hepatica with purified native and recombinant antigens related to fatty acid binding proteins.

Comparative infectivity of Fasciola hepatica metacercariae from isolates of the main and secondary reservoir animal host species in the Bolivian Altiplano high human endemic region

Fascioliasis due to Fasciola hepatica (Linnaeus, 1758) is an endemic disease on the Northern Bolivian Altiplano, where human prevalences and intensities are the highest known, sheep and cattle are the main reservoir hosts, and pigs and donkeys the secondary ones. Investigations were carried out to study the viability of metacercariae experimentally obtained from eggs shed by naturally infected Altiplanic sheep, cattle, pigs and donkeys. A total of 157 Wistar rats were infected with doses of 5, 10, 20 and 150 metacercariae. Metacercariae aged for different number of weeks were used to analyse the influence of age on their viability. The number of worms successfully developed in each rat was established by dissection. Results obtained show that metacercarial infectivity is dependent upon storage time, being lower when metacercariae are older. The maximum longevity is 31 weeks using doses of 20 metacercariae per rat and 48 weeks with 150 metacercariae per rat, although in the latter case only a very low percentage of worms is recovered. Age-related infectivity of metacercariae from Altiplanic F. hepatica does not significantly differ from that of the liver fluke in lowlands of other countries. Concerning the influence of the isolate according to host species, results indicate that metacercarial viabilities of pig and donkey isolates are similar to the viabilities of metacercariae of sheep and cattle isolates. Thus, pig and donkey have a high transmission potential capacity concerning this aspect. This fact is of great importance for the control of human and animal fascioliasis in this highly endemic zone.

Fasciolicidal efficacy of Albizia anthelmintica and Balanites aegyptiaca compared with albendazole

An attempt was made to evaluate the oral doses of 9 g/kg-body weight of Albizzia anthelmintica Brong. Mimoaseae stem bark water extract and 9 g/kg body weight of B. aegyptiaca (L) Del. (Balanitaceae) fruit mesocarp water extract (traditionally used as an anthelmintic in the Sudan) compared with 20 mg/kg body weight (recommended dose) of albendazole against Fasciola gigantica adult worm (12 weeks old) in five groups each of three goats (6 month old). Group (I) uninfected control, group (II) infected untreated control, group (III, IV and V) infected and treated as mentioned above respectively. Based on the percentage reduction in fluke counts from the liver post mortum 2 weeks after treatment, the efficacy of the mentioned therapeutics was 95.5, 93.2 and 97.7%, respectively. The characteristic lesions of liver fasciolosis, egg/gm of faeces (EPG), packed cell volume (PCV), haemoglobin concentration, total red blood cells count (RBC), total white blood cells count (WBC) and oesinophil% were significantly different from control and treated groups (P<0.05).

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.

Effect of experimental fasciolosis on antipyrine metabolism and clearance in water buffaloes

The effect of chronic Fasciola hepatica infection on the metabolism of antipyrine, a marker of microsomal oxidative metabolism, was investigated in male water buffaloes dosed daily with 60 F. hepatica metacercariae over 20 days. The plasma elimination half-life of antipyrine was significantly elevated by 23% at 11 weeks postinfection (p.i.) but did not significantly differ from the control period at 20 weeks p.i. The systemic clearance of antipyrine decreased by 48% at 11 weeks p.i. and then returned to normal. The renal clearance for each of the main antipyrine metabolites decreased at 11 weeks p.i. (hydroxymethylantipyrine (HMA), -42%; norantipyrine (NORA), -58%; and 4-hydroxyantipyrine (OHA), -70%) and did not significantly differ from the control period at 20 weeks p.i. These findings indicate that experimental subclinical fasciolosis leads to altered antipyrine kinetics and to an inhibition of the different antipyrine metabolic pathways in water buffaloes.

The hispid cotton rat (Sigmodon hispidus) as an experimental host for the bovine liver fluke (Fasciola hepatica)

The results of a study testing the susceptibility of the hispid cotton rat, Sigmodon hispidus, to infection with Fasciola hepatica are described. Ten cotton rats were placed into one of four test groups, one uninfected control or three animals each receiving two, five, or 10 F. hepatica metacercariae. Three of nine (33%) became infected, and two of these animals carried the infection to patency. At necropsy one animal had two mature F. hepatica within the common bile duct, and the other harbored a single fluke. Gross and microscopic changes, primarily of the liver, associated with infection are described, as are fecal egg counts throughout the duration of infection.

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.

Standardization of a dot immunoperoxidase assay for field diagnosis of Fasciola hepatica infected cattle

A dot immunoperoxidase assay was developed for the detection of bovine specific antibodies to Fasciola hepatica. The standardization of the assay was done with 298 bovine sera, from seven different groups, previously studied by the reference enzyme-linked immunosorbent assay (ELISA). F. hepatica surface antigens purified by negative affinity against epitopes shared with Paramphistomum spp. and Echinococcus granulosus were used. Starting with sensitized and blocked nitrocellulose strips, the dot immunoperoxidase (DI) assay requires 2 h 15 min at room temperature. The development of a distinct brown dot indicated a positive reaction. The DI test showed a sensitivity of 82%, a specificity of 90%, with a 95% confidence level (CL), good repeatability (kappa 0.741, CL 95%), as well as a significant association with the reference ELISA (kappa 0.618, CL 95%). The DI assay is fast, simple and has a low cost - all convenient characteristics for a screening test to be used in the field.

The Northern Bolivian Altiplano: a region highly endemic for human fascioliasis

The worldwide importance of human infection by Fasciola hepatica has been recognized in recent years. The endemic region between Lake Titicaca and the valley of La Paz, Bolivia, at 3800-4100 m altitude, presents the highest prevalences and intensities recorded. Large geographical studies involving Lymnaea truncatula snails (malacological, physico-chemical, and botanic studies of 59, 28 and 30 water bodies, respectively, inhabited by lymnaeids; environmental mean temperature studies covering a 40-year period), livestock (5491 cattle) and human coprological surveys (2723 subjects, 2521 of whom were school children) were conducted during 1991-97 to establish the boundaries and distributional characteristics of this endemic Northern Altiplano region. The endemic area covers part of the Los Andes, Ingavi, Omasuyos and Murillo provinces of the La Paz Department. The human endemic zone is stable, isolated and apparently fixed in its present outline, the boundaries being marked by geographical, climatic and soil-water chemical characteristics. The parasite distribution is irregular in the endemic area, the transmission foci being patchily distributed and linked to the presence of appropriate water bodies. Prevalences in school children are related to snail population distribution and extent. Altiplanic lymnaeids mainly inhabit permanent water bodies, which enables parasite transmission during the whole year. A confluence of several factors mitigates the negative effects of the high altitude.