Changes in the Populations of Two Lymnaeidae and Their Infection by Fasciola hepatica and/or Calicophoron daubneyi over the Past 30 Years in Central France

Field investigations were carried out during three periods (from 1976 to 1997, in 2013-2014, and in 2020-2021) on 39 cattle-raising farms on acidic soils to track changes in the populations of two Lymnaeidae (Galba truncatula and Omphiscola glabra) and their infection with Fasciola hepatica and/or Calicophoron daubneyi. Compared to the survey between 1976 and 1997 on these farms, there was a significant decrease in the number of the two lymnaeid populations and the size of the G. truncatula populations in both 2013-2014 and 2020-2021. This decline was significantly faster in the last nine years than it was before 2013. The area of habitats colonized by G. truncatula showed no significant variation over the years, while that of habitats with O. glabra significantly decreased in the period covered by the three surveys. The prevalence of F. hepatica infection in snails significantly decreased over the years, while C. daubneyi infection increased over time in both lymnaeid species. These changes are due to the use of triclabendazole to treat fasciolosis in ruminants since the 1990s, and are probably a consequence of the successive heatwaves that have occurred since 2018 in the region.

[A Retrospective Study on Planorbarius metidjensis and Its Role as a Potential Intermediate Host in the Transmission of Schistosoma haematobium in the Souss-Massa Region (Morocco)]

A retrospective research study was carried out by our team on Planorbarius metidjensis to highlight its epidemiological role as a potential host snail of Schistosoma haematobium in the Souss-Massa region. Contrary to the habitats colonized by Bulinus truncatus, the main host snail, those of P. metidjensis are located at the altitude of above 300 m. The best results of the experimental infections with S. haematobium were obtained using juvenile planorbids of 2 to 3 mm in diameter and a dose of five miracidia per snail. No snail naturally infected with the parasite was found when dissecting 3,457 adult bulinids and 2,470 adult planorbids. Despite the location of its habitats in altitude, P. metidjensis is a potential intermediate host of S. haematobium and it is important to follow these populations, as those of B. truncatus, in the future to avoid possible reoccurrence of indigenous cases of the disease.

Fasciola hepatica: the dispersal of cercariae shed by the snail Galba truncatula

Field investigations in 14 wild watercress beds located in the French region of Limousin, a known endemic area for distomatosis, were performed for three years to determine the distance that cercariae of Fasciola hepatica can reach in water before their encystment on the host plant. Each bed was located on the course of an open drainage furrow, while snails (Galba truncatula) lived upstream around the emergence of a source. Five plant species were collected in early April and examined to find metacercariae. Most cysts were noted on Nasturtium officinale (188 on 48.7 kg of dripped plants), followed by Helosciadium nodiflorum (125 on 33.4 kg). On the other plant species, there were few larvae. Most cercariae encysted on the plants growing in the most upstream part of each bed, usually on the first 50 cm in length. When water in the beds was fast running, the distribution of metacercariae was more limited and their number was fewer than those in the beds fed by a slow flow of water. Cercariae were able to swim or were carried away by the current up to a mean of 5 m in slow-flow waters before encysting; this distance was only 4 m in faster waters. Plants growing on the most upstream section of a watercress bed located in a drainage furrow are the most used by cercariae for their encystment, when snails live around the emergence of a source. The speed of the water current affected the number and distribution of metacercariae in the bed.

Current decline in schistosome and soil-transmitted helminth infections among school children at Loum, Littoral region, Cameroon

Introduction

Soil-transmitted helminth infections (STHs) and schistosomiasis have serious consequences for the health, education and nutrition of children in developing countries. As Loum is known as a highly endemic commune for these infections, several deworming campaigns have been carried out in the past. The purpose of this study was to determine any changes that have occurred since then in the characteristics of these infections among schoolchildren in this site.

Methods

A cross-sectional study was conducted in October 2016 on 289 schoolchildren. Stool and urine samples were collected and examined to determine the prevalence and intensity of helminth infections.

Results

The highest prevalence was noted for Schistosoma haematobium (34.2%), followed by Ascaris lumbricoides (8.6%), S. mansoni (4.9%) and Trichuris trichiura (4.9%) in decreasing order. A prevalence of less than 2% was noted for each of the other two helminths. The highest mean intensity was found for S. haematobium (39.6 eggs/10 ml of urine), followed by A. lumbricoides (24.2 eggs per gram of faeces: epg), Strongyloides stercoralis (16.6 epg) and Schistosoma mansoni (12.3 epg). The prevalence of T. trichiura was significantly higher in boys and that of S. haematobium in children aged 10 years or older, while the differences between other values of prevalence or between egg burdens were not significant.

Conclusion

Compared with values reported in 2003, the prevalence and intensity of schistosomiases and STH infections in Loum has sharply decreased in 2016. Confirmation of this decrease in the years to come allowed to space deworming campaigns among schoolchildren.

Proteome characterization in various biological fluids of Trypanosoma brucei gambiense-infected subjects

Human African trypanosomiasis (HAT) is a neglected tropical disease that is endemic in sub-Saharan Africa. Control of the disease has been recently improved by better screening and treatment strategies, and the disease is on the WHO list of possible elimination. However, some physiopathological aspects of the disease transmission and progression remain unclear. We propose a new proteomic approach to identify new targets and thus possible new biomarkers of the disease. We also focused our attention on fluids classically associated with HAT (serum and cerebrospinal fluid (CSF)) and on the more easily accessible biological fluids urine and saliva. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) established the proteomic profile of patients with early and late stage disease. The serum, CSF, urine and saliva of 3 uninfected controls, 3 early stage patients and 4 late stage patients were analyzed. Among proteins identified, in CSF, urine and saliva, respectively, 37, 8 and 24 proteins were differentially expressed and showed particular interest with regards to their function. The most promising proteins (Neogenin, Neuroserpin, secretogranin 2 in CSF; moesin in urine and intelectin 2 in saliva) were quantified by enzyme-linked immunosorbent assay in a confirmatory cohort of 14 uninfected controls, 23 patients with early stage disease and 43 patients with late stage disease. The potential of two proteins, neuroserpin and moesin, with the latter present in urine, were further characterized. Our results showed the potential of proteomic analysis to discover new biomarkers and provide the basis of the establishment of a new proteomic catalogue applied to HAT-infected subjects and controls. SIGNIFICANCE: Sleeping sickness, also called Human African Trypanosomiasis (HAT), is a parasitic infection caused by a parasitic protozoan, Trypanosoma brucei gambiense or T. b. rhodesiense which are transmitted via an infected tsetse fly: Glossina. For both, the haemolymphatic stage (or first stage) signs and symptoms are intermittent fever, lymphadenopathy, hepatosplenomegaly, headaches, pruritus, and for T. b. rhodesiense infection a chancre is often formed at the bite site. Meningoencephalitic stage (or second stage) occurs when parasites invade the CNS, it is characterised by neurological signs and symptoms such as altered gait, tremors, neuropathy, somnolence which can lead to coma and death if untreated. first stage of the disease is characterizing by fevers, headaches, itchiness, and joint pains and progressive lethargy corresponding to the second stage with confusion, poor coordination, numbness and trouble sleeping. Actually, diagnosing HAT requires specialized expertise and significant resources such as well-equipped health centers and qualified staff. Such resources are lacking in many endemic areas that are often in rural locales, so many individuals with HAT die before the diagnosis is established. In this study, we analysed by mass spectrometry the entire proteome of serum, CSF, urine and saliva samples from infected and non-infected Angolan individuals to define new biomarkers of the disease. This work of proteomics analysis is a preliminary stage to the characterization of the whole proteome, of these 4 biological fluids, of HAT patients. We have identified 69 new biomarkers. Five of them have been thoroughly investigated by ELISA quantification. Neuroserpine and Moesin are respectively promising new biomarkers in CSF and urine's patient for a better diagnosis.

Determination of zones at risk for fasciolosis in the department of Haute-Vienne, central France: a retrospective study on natural infections detected in 108,481 Galba truncatula for 37 years

A retrospective study on the natural infection of Galba truncatula by Fasciola hepatica was carried out in the French department of Haute-Vienne to determine whether there are areas at risk for fasciolosis. Adult snails included in this analysis came from samples collected from pastures on 259 farms and from 121 wild watercress beds between 1970 and 2006. Fasciola hepatica infection rates were examined in relation to altitude and climatic data (mean annual rainfall, mean annual temperature) of each municipality. In a total of 108,481 snails collected in 151 municipalities, the overall prevalence of infection was 3.8% but varied according to the municipalities from which samples were taken (from 1% to 7.4%). The prevalence of F. hepatica infection in snails significantly decreased when the mean altitude of municipalities or their mean annual rainfall increased. However, this prevalence significantly increased with increasing mean annual temperatures. Studying the prevalence of infection in these snails makes it possible to delineate zones at risk for fasciolosis on the acid soils of Haute-Vienne. The risk of infection for livestock would be greater in areas of Haute-Vienne below 400 m above sea level and would gradually decrease when the altitude of the land increases.

Toxoplasma gondii survey in cats from two environments of the city of Rio de Janeiro, Brazil by Modified Agglutination Test on sera and filter-paper

Background

Toxoplasma gondii is a protozoan with a worldwide distribution, in warm-blood animals, including humans. Local conditions and environmental disturbances may influence transmission dynamics of a zoonotic agent. This study evaluates the epidemiology of T. gondii based on toxoplasmosis prevalence in two populations of cats living in distinct urbanization conditions in Rio de Janeiro, Brazil.

Methods

Among 372 domestic cats sampled, 265 were from a public shelter located downtown Rio and 107 from a relatively preserved wild environment in a residential area. Sera and eluates from dried blood spots were tested for detection of IgG antibodies against T. gondii by modified agglutination test (MAT).

Results

Antibodies to T. gondii were detected in 32/265 (12.08%) animals from the public shelter and in 4/107 (3.74%) cats from the residential area. Identical results were observed for sera and eluates.

Conclusions

Filter paper provides a reliable accurate alternative storage option when conditions of sample collection and transportation in the field are unfavorable. The significantly lower prevalence in the residential area is discussed in terms of environmental, biological and behavioral features.

Current decline in the number and size of Galba truncatula and Omphiscola glabra populations, intermediate hosts of Fasciola hepatica, on the acidic soils of Central France

Field investigations on the habitats colonized by Galba truncatula or Omphiscola glabra were carried out on 162 farms of the Limousin region, Central France, to determine whether there is currently a decline in the number and size of snail populations. Seven types of snail habitats were considered here. Compared to the numbers of snail populations recorded from 1976 to 1992, the values noted from 2013 to 2016 were significantly lower, with a decline rate of 34% for G. truncatula and 23% for O. glabra. Variations in this decline rate with the type of snail habitat were also noted. The greatest decreases in the numbers of snail populations were noted for spring heads located in meadows and for road ditches, while the lowest were noted for open drainage furrows present in meadows. The distribution of these habitats according to their area did not show any significant change over time. In contrast, overwintering snails were significantly less numerous in 2013-2016 in five types of habitats for G. truncatula and in three types only for O. glabra. Several causes underlie this population decline. Among them, the current development of mechanical cleaning in open drainage systems and road ditches, that of subsurface drainage in meadows, and regular gyro-crushing of vegetation around temporary spring heads were the most important.

Larval trematode infections in Lymnaea glabra populations living in the Brenne Regional Natural Park, central France

Lymnaea glabra is known to be a natural intermediate host of two flukes, Calicophoron daubneyi and Fasciola hepatica, in central France. But it can also sustain larval development of other digeneans. Adult snails were thus collected from 206 habitats in 2014 and 2015 to identify parasite species and determine the prevalence of each digenean infection in relation to the five types of snail habitats. Seven digenean species were noted in 321 infected snails (out of 17,647 L. glabra). Snails with F. hepatica or C. daubneyi were found in 14.5% and 12.6% of habitats, respectively. Percentages were lower for snails with Opisthoglyphe ranae (5.8%), Haplometra cylindracea (5.3%) and were less than 5% for those infected with Echinostoma revolutum, Notocotylus sp. or Plagiorchis sp. Prevalence noted for each parasite species varied with the type of habitat. The number of species in L. glabra was lower than that found in G. truncatula from the same region (7 instead of 10). The distribution and prevalence of each digenean species were thus dependent on the type and location of each snail habitat.

Interferon gamma effect on immune mediator production in human nerve cells infected by two strains of Toxoplasma gondii

Interferon gamma (IFN-γ) is the major immune mediator that prevents toxoplasmic encephalitis in murine models. The lack of IFN-γ secretion causes reactivation of latent T. gondii infection that may confer a risk for severe toxoplasmic encephalitis. We analyse the effect of IFN-γ on immune mediator production and parasite multiplication in human nerve cells infected by tachyzoites of two T. gondii strains (RH and PRU). IFN-γ decreased the synthesis of MCP-1, G-CSF, GM-CSF and Serpin E1 in all cell types. It decreased IL-6, migration inhibitory factor (MIF) and GROα synthesis only in endothelial cells, while it increased sICAM and Serpin E1 synthesis only in neurons. The PRU strain burden increased in all nerve cells and in contrast, RH strain replication was controlled in IFN-γ-stimulated microglial and endothelial cells but not in IFN-γ-stimulated neurons. The proliferation of the PRU strain in all stimulated cells could be a specific effect of this strain on the host cell.

Fasciola hepatica: comparative metacercarial productions in experimentally-infected Galba truncatula and Pseudosuccinea columella

As large numbers of metacercariae of Fasciola hepatica are necessary for research, experimental infections of Galba truncatula and Pseudosuccinea columella with this digenean were carried out to determine the better intermediate host for metacercarial production and, consequently, the most profitable snail for decreasing the cost price of these larvae. Pre-adult snails (4 mm in shell height) originating from two populations per lymnaeid species were individually exposed to two or five miracidia, raised at 23 °C and followed for cercarial shedding up to their death. Compared to values noted in G. truncatula, the survival of P. columella on day 30 post-exposure was significantly greater, while the prevalence of F. hepatica infection was significantly lower. In the four P. columella groups, metacercarial production was significantly greater than that noted in the four groups of G. truncatula (347-453 per cercariae-shedding snail versus 163-275, respectively). Apart from one population of G. truncatula, the use of five miracidia per snail at exposure significantly increased the prevalence of F. hepatica in P. columella and the other population of G. truncatula, whereas it did not have any clear effect on the mean number of metacercariae. The use of P. columella for experimental infections with F. hepatica resulted in significantly higher metacercarial production than that noted with G. truncatula, in spite of a lower prevalence for the former lymnaeid. This finding allows for a significant decrease in the cost price of these larvae for commercial production.

Detection of Toxoplasma gondii DNA in horse meat from supermarkets in France and performance evaluation of two serological tests

In France, some cases of severe toxoplasmosis have been linked to the consumption of horse meat that had been imported from the American continent where atypical strains of Toxoplasma gondii are more common than in Europe. Many seroprevalence studies are presented in the literature but risk assessment of T. gondii infection after horse meat consumption is not possible in the absence of validated serological tests and the unknown correlation between detection of antibodies against T. gondii and presence of tissue cysts. We performed magnetic-capture polymerase chain reaction (MC-PCR) to detect T. gondii DNA in 231 horse meat samples purchased in supermarkets in France and evaluated the performance and level of agreement of the modified agglutination test (MAT) and enzyme-linked immunosorbent assay (ELISA) in the meat juices. The serological tests lacked sensitivity, specificity, and agreement between them, and there was no correlation with the presence of T. gondii DNA in horse meat, raising concerns about the reliability of T. gondii seroprevalence data in horses from the literature. T. gondii DNA was detected in 43% of horse meat samples but the absence of strain isolation in mice following inoculation of more than 100 horse meat samples suggests a low distribution of cysts in skeletal muscles and a low risk of T. gondii infection associated with horse meat consumption. However, to avoid any risk of toxoplasmosis, thorough cooking of horse meat is recommended.

Pseudosuccinea columella: age resistance to Calicophoron daubneyi infection in two snail populations

Individual infections of Egyptian and French Pseudosuccinea columella with five miracidia of Calicophoron daubneyi were carried out to determine whether this lymnaeid was capable of sustaining larval development of this parasite. On day 42 post-exposure (at 23 °C), infected snails were only noted in groups of individuals measuring 1 or 2 mm in height at miracidial exposure. Snail survival in the 2-mm groups was significantly higher than that noted in the 1-mm snails, whatever the geographic origin of snail population. In contrast, prevalence of C. daubneyi infection was significantly greater in the 1-mm groups (15-20% versus 3.4-4.0% in the 2-mm snails). Low values were noted for the mean shell growth of infected snails at their death (3.1-4.0 mm) and the mean number of cercariae (<9 in the 1-mm groups, <19 in the 2-mm snails). No significant differences between snail populations and snails groups were noted for these last two parameters. Most infected snails died after a single cercarial shedding wave. Both populations of P. columella showed an age resistance to C. daubneyi infection and only juveniles measuring 2 mm or less in shell height at exposure can ensure larval development of this digenean up to cercarial shedding.

Ruminal paramphistomosis in cattle from northeastern Algeria: prevalence, parasite burdens and species identification

Slaughterhouse samples were analysed over a two-year period (September 2010-August 2012) in Jijel (northeastern Algeria) in order to determine seasonal variations in the prevalence and intensity of bovine paramphistomosis in a Mediterranean climate and identify paramphistome species using molecular biology. In spring and summer, significantly higher prevalences and lower parasite burdens were noted in bull calves, thus indicating an effect of season on these parameters. In contrast, the differences among seasonal prevalences or among seasonal parasite burdens were not significant in the case of old cows. Eleven adult worms from the slaughterhouses of Jijel and three neighbouring departments (Constantine, El Tarf and Setif) were analysed using molecular markers for species identification. Two different species, Calicophoron daubneyi and C. microbothrium, were found. The presence of these two paramphistomids raises the question of their respective frequency in the definitive host and local intermediate hosts.

Adaptation of Lymnaea fuscus and Radix balthica to Fasciola hepatica through the experimental infection of several successive snail generations

BACKGROUND

High prevalence of Fasciola hepatica infection (>70%) was noted during several outbreaks before the 2000s in several French farms where Galba truncatula is lacking. Other lymnaeids such as Lymnaea fuscus, L. glabra and/or Radix balthica are living in meadows around these farms but only juvenile snails can sustain complete larval development of F. hepatica while older snails were resistant. The low prevalence of infection (<20%) and limited cercarial production (<50 cercariae per infected snail) noted with these juveniles could not explain the high values noted in these cattle herds. As paramphistomosis due to Calicophoron daubneyi was not still noted in these farms, the existence of another mode of infection was hypothesized. Experimental infection of several successive generations of L. glabra, originating from eggs laid by their parents already infected with this parasite resulted in a progressive increase in prevalence of snail infection and the number of shed cercariae. The aim of this paper was to determine if this mode of snail infection was specific to L. glabra, or it might occur in other lymnaeid species such as L. fuscus and R. balthica.

METHODS

Five successive generations of L. fuscus and R. balthica were subjected to individual bimiracidial infections in the laboratory. Resulting rediae and cercariae in the first four generations were counted after snail dissection at day 50 p.e. (20°C), while the dynamics of cercarial shedding was followed in the F5 generation.

RESULTS

In the first experiment, prevalence and intensity of F. hepatica infection in snails progressively increased from the F1 (R. balthica) or F2 (L. fuscus) generation. In the second experiment, the prevalence of F. hepatica infection and the number of shed cercariae were significantly lower in L. fuscus and R. balthica (without significant differences between both lymnaeids) than in G. truncatula.

CONCLUSION

The F. hepatica infection of several successive snail generations, coming from parents infected with this parasite, resulted in a progressive increase in prevalence and intensity of snail infection. This may explain high prevalence of fasciolosis noted in several cattle-breeding farms when the common snail host of this digenean, G. truncatula, is lacking.

In vitro infection of human nervous cells by two strains of Toxoplasma gondii: a kinetic analysis of immune mediators and parasite multiplication

The severity of toxoplasmic infection depends mainly on the immune status of the host, but also on the Toxoplasma gondii strains, which differ by their virulence profile. The relationship between the human host and T. gondii has not yet been elucidated because few studies have been conducted on human models. The immune mechanisms involved in the persistence of T. gondii in the brains of immunocompetent subjects and during the reactivation of latent infections are still unclear. In this study, we analyzed the kinetics of immune mediators in human nervous cells in vitro, infected with two strains of T. gondii. Human neuroblast cell line (SH SY5Y), microglial (CMH5) and endothelial cells (Hbmec) were infected separately by RH (type I) or PRU (type II) strains for 8 h, 14 h, 24 h and 48 h (ratio 1 cell: 2 tachyzoites). Pro-inflammatory protein expression was different between the two strains and among different human nervous cells. The cytokines IL-6, IL-8 and the chemokines MCP-1 and GROα, and SERPIN E1 were significantly increased in CMH5 and SH SY5Y at 24 h pi. At this point of infection, the parasite burden declined in microglial cells and neurons, but remained high in endothelial cells. This differential effect on the early parasite multiplication may be correlated with a higher production of immune mediators by neurons and microglial cells compared to endothelial cells. Regarding strain differences, PRU strain, but not RH strain, stimulates all cells to produce pro-inflammatory growth factors, G-CSF and GM-CSF. These proteins could increase the inflammatory effect of this type II strain. These results suggest that the different protein expression profiles depend on the parasitic strain and on the human nervous cell type, and that this could be at the origin of diverse brain lesions caused by T. gondii.

Radix natalensis: the effect of Fasciola hepatica infection on the reproductive activity of the snail

Experimental infections of Egyptian Radix natalensis (shell height at miracidial exposure: 4 mm) with a French isolate of Fasciola hepatica were carried out under laboratory conditions at 22 °C to specify the characteristics and follow the dynamics of their egg-laying. Controls constituted unexposed R. natalensis of the same size. No significant difference between controls and the uninfected snails of the exposed group was noted, whatever the parameter considered. In controls and exposed snails, the dates of the first egg masses were close to each other (56.4–65.3 days). In contrast, the life span of snails and the length of the egg-laying period were significantly shorter and egg production was significantly lower in infected R. natalensis than in controls and uninfected snails. In infected R. natalensis, but without cercarial shedding (NCS snails), egg production was irregular throughout the egg-laying period. In cercarial-shedding (CS) snails, the first egg masses were laid before the first cercarial emergence (at a mean of 56 days and 67 days, respectively). Thereafter, egg mass production of CS snails was irregular up to day 72 of the experiment, stopped during the following two weeks and started again after day 88 for a single snail. In conclusion, the F. hepatica infection of R. natalensis reduced the reproductive activity in both NCS and CS snails. The pattern noted for egg production in infected R. natalensis seems to be species-specific because of the high shell size of this lymnaeid and its role as an atypical intermediate host in the life cycle of the parasite.

Fasciola hepatica: development of redial generations in experimental infections of Pseudosuccinea columella

Experimental infections of Egyptian Pseudosuccinea columella with one or two miracidia of Fasciola hepatica per snail were carried out to determine the developmental pattern (normal or abnormal) of redial generations and specify the number of free rediae developing in snails according to their generation. Controls were constituted by a French population of Galba truncatula infected according to the same protocol. Most infected P. columella showed a normal development of redial generations (96.2-98.1 vs 75.5-85.7% for G. truncatula). In each redial category, free rediae were more numerous in P. columella than in G. truncatula, and their number were also greater in the two-miracidia groups than in single-miracidium infections for each lymnaeid considered separately. This increase in redial production was mainly due to the number of first mother (R1a) rediae producing daughter rediae only: 2 per P. columella (vs one redia in G. truncatula) in single-miracidium groups and 3.1 (vs 1.9) in the two-miracidia groups. In P. columella, the mean total number of free rediae developing in single-miracidium and bimiracidial infections was 77.2 and 117.6, respectively (instead of 33.5 and 52.1 rediae in G. truncatula). The number of F. hepatica rediae present in P. columella was related to the number of fully grown sporocysts and the quantity of R1a rediae which developed into the snail body.

Lymnaea cubensis, an experimental intermediate host for Fascioloides magna

Single-miracidium infections of Lymnaea cubensis (Pfeiffer) from Guadeloupe with the giant liver fluke Fascioloides magna (Bassi, 1875) (Digenea) were carried out during five successive snail generations to determine if this lymnaeid might sustain complete larval development of the parasite. Controls were constituted by a French population of Galba truncatula (Miller) (a single generation) infected according to the same protocol. It was recorded that prevalence and intensity of F. magna infection in L. cubensis progressively increased from F1 to F5 generations. Cercarial shedding of F. magna was noted only within F5 generation of L. cubensis. However, most measured parameters of infection in this species were significantly lower than those noted for G. truncatula and most L. cubensis died after a single shedding wave. Despite this, L. cubensis can be added to the list of potential intermediate hosts of F. magna.

Fasciola hepatica: effect of the natural light level on cercarial emergence from temperature-challenged Galba truncatula

As abrupt changes in water temperature (thermal shock) triggered a significantly greater cercarial emergence of Fasciola hepatica from experimentally infected Galba truncatula, laboratory investigations were carried out to study the influence of light on cercarial emergence in snails subjected to a thermal shock every week (a mean of 12 °C for 3 h) during the patent period. Thermal shock for these temperature-challenged (TC) snails was carried out outdoors under artificial or natural light, or indoors under constant artificial light. Compared with the infected control snails always reared indoors at 20 °C, the number of cercariae in TC snails subjected to a thermal shock and natural light outdoors was significantly greater. The repetition of this experiment by subjecting TC snails to the same thermal shock indoors under an artificial light level ranging from 600 to 3000 lux did not show any significant difference among the numbers of cercariae in the different subgroups. A detailed analysis of the results noted in the TC snails subjected to natural light during the thermal shock demonstrated that the number of cercariae-releasing snails was significantly higher between 601 and 1200 lux and for the highest nebulosity values (7–8 octas, which corresponds to a sufficiently or completely overcast sky). Contrary to the intensity of artificial light, which did not influence cercarial emergence, the natural light level had a significant effect on this process when F. hepatica-infected snails were subjected to a regular thermal shock during the patent period.

Fasciola hepatica: variations in redial development and cercarial production in relation to the geographic origin of the parasite

Two hundred Galba truncatula, originating from a French population, were subjected to single-miracidium infections with an allopatric isolate (origin, Argentina) of Fasciola hepatica. The control group was constituted by 100 snails coming from the same population and exposed to sympatric miracidia of F. hepatica according to the same protocol. Snail samples were collected bimonthly from both groups between day 14 and day 112 p.e. (at 20 °C) and snail dissections were performed to count free rediae, intraredial morulae and free cercariae. Third and fourth generation rediae were significantly more numerous in the allopatric group, while the number of first generation rediae was significantly lower. In the sympatric group, the decrease in the number of intraredial morulae in the first, second and third redial generations was significantly faster. Free cercariae within the snail body were significantly more numerous in the sympatric than in the allopatric groups, whatever the date of snail dissection. The changes in redial development and cercarial production noted in the Argentinean group might be due to the evolution of South American flukes in a divergent way after the introduction of foreign infected ruminants in this continent from the 15th century.

Consequence of temperature changes on cercarial shedding from Galba truncatula infected with Fasciola hepatica or Paramphistomum daubneyi

Experimental infections of Galba truncatula (two populations) with Fasciola hepatica or Paramphistomum daubneyi were carried out to study the effect of water temperature changes (3 h at a mean of 12 °C every week) on cercarial shedding during the patent period. The results were compared with those of control snails infected according to the same protocol and always maintained at 20 °C. Compared to controls, a significant increase in the number of cercariae-shedding snails, a significantly longer patent period and significantly greater cercarial production were noted in temperature-challenged snails, regardless of the type of digenean infection. In contrast, the number of incompletely formed metacercariae was significantly higher in temperature-challenged snails than in controls. Incompletely formed metacercariae of F. hepatica consisted of cysts whose colour remained whitish after shedding (25.4% for temperature-challenged snails) or whose dome was flattened after encystment (74.6%). Those of P. daubneyi were totally dark brown or blackish after formation. These incomplete metacercariae might originate from young differentiating cercariae within the snail body (F. hepatica) or from cercariae which died just after encystment (P. daubneyi). The use of regular temperature changes for snails infected with F. hepatica or P. daubneyi must be monitored carefully during collection of metacercariae to select completely formed cysts for infecting definitive hosts.

Comparative strategies and success of sympatric and allopatric Fasciola hepatica infecting Galba truncatula of different susceptibilities

Allopatric infections of French Galba truncatula with an Argentinean isolate of Fasciola hepatica were carried out to determine the infectivity of foreign miracidia in three snail populations differing by their susceptibility to French miracidia (two highly and one poorly susceptible populations). Sympatric infections of G. truncatula with French miracidia were used as controls. Compared to sympatric infections of G. truncatula, snail survival at day 30 post-infection in allopatric groups was significantly lower in a highly susceptible population and significantly greater in the other two. Prevalence in snails infected with the allopatric isolate was significantly lower (16.4-34.5 % instead of 58.6-72.1 %), whereas their patent period was significantly longer (a mean of 69.9-85.9 days instead of 6.4-20.7 days). The mean number of metacercariae was also higher in allopatric groups (236.5-897.3 per cercariae-shedding snail instead of 70.7-222.1). Owing to longer patent periods, the Argentinean isolate of F. hepatica was less pathogenic for these snails. The lower prevalence of infection, the longer patent period and the higher number of metacercariae noted in allopatric groups might be the consequence of an adaptive mechanism used by this digenean introduced to the New World to infect new populations of unusual intermediate hosts.

Local adaptation of the trematode Fasciola hepatica to the snail Galba truncatula

Experimental infections of six riverbank populations of Galba truncatula with Fasciola hepatica were carried out to determine if the poor susceptibility of these populations to this digenean might be due to the scarcity or the absence of natural encounters between these snails and the parasite. The first three populations originated from banks frequented by cattle in the past (riverbank group) whereas the three others were living on islet banks without any known contact with local ruminants (islet group). After their exposure, all snails were placed in their natural habitats from the end of October up to their collection at the beginning of April. Compared to the riverbank group, snails, which died without cercarial shedding clearly predominated in the islet group, while the other infected snails were few in number. Most of these last snails released their cercariae during a single shedding wave. In islet snails dissected after their death, the redial and cercarial burdens were significantly lower than those noted in riverbank G. truncatula. Snails living on these islet banks are thus able to sustain larval development of F. hepatica. The modifications noted in the characteristics of snail infection suggest the existence of an incomplete adaptation between these G. truncatula and the parasite, probably due to the absence of natural contact between host and parasite.

Paramphistomum daubneyi: characteristics of infection in three lymnaeid species

Experimental infections of two South American lymnaeids (Lymnaea neotropica and L. viatrix var. ventricosa) with Paramphistomum daubneyi were carried out to determine if these snail species could sustain larval development of this digenean and, if so, to specify their potential for cercarial production. A French population of Galba truncatula infected and raised according to the same protocol served as controls. In both experiments, prevalence of P. daubneyi infections in snails did not significantly differ from each other. In snail groups evaluated for cercarial shedding (first experiment), a significantly lower number of shed cercariae was noted for L. neotropica, while those from G. truncatula and L. v. ventricosa did not differ significantly from each other. Dissection of infected snails at day 65 post-exposure at 20 °C (second experiment) found significantly lower burdens of P. daubneyi rediae and cercariae in the bodies of L. neotropica than in those of G. truncatula and L. v. ventricosa. Compared to total cercarial production observed in dissected snails, the percentage of cercariae which exited from snails was 75.6% for G. truncatula, 21.6% for L. neotropica, and 91.4% for L. v. ventricosa. This last species seems to be a good candidate for metacercarial production of P. daubneyi.

Results of an action-research on epilepsy in rural Mali

Purpose

To evaluate the RARE (Réseau Action-Recherche sur l’Epilepsie) program, a model of managing and treating people with epilepsy (PWE) at a primary health-care level in rural areas of Mali, we assessed treatment efficacy and compliance of patients who underwent the first year follow-up.

Methods

A network of rural general practitioners (GPs) settled in six rural districts of the regions of Koulikoro, Segou and Sikasso, was involved in the diagnosis, evaluation and monitoring of all the identified PWE and in the distribution of phenobarbital (PB). All the participants were included in a prospective database and followed-up by GPs at 4 months intervals during the first year. Seizure frequency, treatment doses and appearance of adverse events (AEs) were systematically recorded. Efficacy was evaluated in terms of reduction of seizures frequency while noncompliance in terms of time to study withdrawal for any cause.

Key findings

596 patients treated with PB were included in the analysis. Of these, 74.0% completed the first year follow-up. At the final visit, 59.6% were seizure-free: 31.0% for 12 months, 10.2% for 8 months and 18.4% for 4 months. Adults and patients with convulsive seizures were the most drug-resistant (p<0.002). Few AEs were recorded. The multivariate analysis showed that being a woman, presenting convulsive seizures, having more than 5 seizures/month and had never be treated were predictors of withdrawal (p≤0.05) at 12 months.

Significance

This study showed a good response and compliance to the treatment and allowed the identification of some factors associated with failure of management in a setting very near to clinical practice. Awareness campaigns are needed to assure a broader accessibility to treatment and to improve the compliance and continuity with treatment programs.

Haplometra cylindracea (Zeder, 1800) (Trematoda:Plagiorchiidae): variation in the dates of cercarial shedding for overwintering Galba truncatula

Natural infections of Galba truncatula with Haplometra cylindracea were followed from 2001 to 2009 to determine if their characteristics were similar when snails came from water collections frequented by Bufo bufo or by frogs and newts for their egg-laying. Snail samples were collected from both types of sites to count shed cercariae for three days and also free cercariae when snails were dissected. In sites only frequented by B. bufo, cercarial shedding occurred earlier than in those colonized by frogs and newts (March instead of April-May). In contrast, the number of cercariae shed during three successive days was significantly higher in May. This variation in the dates of cercarial shedding might be due, either to a synchronism between cercaria-releasing snails and the presence of the definitive host (tadpoles) in water collections, or to an earlier infection of overwintering snails in autumn by H. cylindracea miracidia in the case of toad-frequented sites.

The redial and cercarial production of a digenean in the snail host is lower when no cercarial shedding occurs

Single- and double-miracidium exposures of Galba truncatula with Fasciola hepatica (two groups) or with Paramphistomum daubneyi (two groups) were carried out under laboratory conditions to compare parasite production in cercaria-shedding snails (CS snails) with that found in snails without emission (NCS snails). Free rediae and cercariae were thus counted in snails from both categories after their dissection at regular intervals (at 24 degrees C). In the four groups, the numbers of free rediae and free cercariae found at day 75 post-exposure (F. hepatica) or at day 85 (P. daubneyi) were significantly greater in CS snails than in NCS ones. The number of cercariae in NCS subgroups did not show any significant variation from day 45 p.e. to day 75 (F. hepatica, the two groups) or from day 55 to day 85 (P. daubneyi, single-miracidium infections), while it significantly decreased with increasing time of infection in the double-miracidium infections with P. daubneyi. In NCS snails, the presence of too numerous free cercariae within the snail's body (the volume of the body allows development only of a given number of rediae) might rapidly block out redial development and intraredial differentiation of other cercariae. The numerical diminution of P. daubneyi cercariae in the NCS snails (double-miracidium group) might probably be due to the lysis of new cercariae just formed, probably in reason of a lack of nutrients available for these larvae within the snail.

Parasite development and visceral pathology in Galba truncatula co-infected with Fasciola hepatica and Paramphistomum daubneyi

Histological investigations in Galba truncatula naturally or experimentally co-infected with Fasciola hepatica and Paramphistomum daubneyi were carried out to study parasite development and the responses of the digestive gland and kidney of snails, as larval forms of these digeneans often use these two sites for their growth within the snail's body. The number of live rediae per snail ranged from 2.4 to 4.2 for the dominating parasite (it developed in the digestive gland) and was less than 2.0 for the other species. When the dominating species was F. hepatica, most snails harboured cercariae-containing rediae; if this parasite was P. daubneyi, procercariae-containing rediae with or without free procercariae were observed in most snails. In contrast, most rediae of the other species were immature. The pathology caused by the dominating species in the digestive gland was greater than that recorded in the kidney, where the other parasite was generally located. The most frequent tissue lesions in the digestive gland were generalized epithelial necrosis and epithelial reconstitution. In the kidney, multifocal epithelial necrosis was frequently observed, particularly when P. daubneyi was the dominating species. The frequencies of lesions in the digestive gland agreed with percentages reported by our team in other snails mono-infected with F. hepatica or P. daubneyi. In contrast, multifocal necrosis in the kidney was clearly greater in the present study and this finding might be explained by assuming that a sufficient number of free larvae within the snail would be necessary for the development of epithelial necrosis in the whole kidney.

Fasciola hepatica: the infectivity of cattle-origin miracidia had increased over the past years in central France

A retrospective study on experimental infections of Galba truncatula, originating from four populations, was carried out to determine the infectivity of Fasciola hepatica miracidia in snails either subjected to single-miracidium or bimiracidial exposures in 2006 and to compare it with results found before 1990 in other experiments using the same protocol. In single-miracidium infections, the prevalence of snail infection was significantly greater in 2006 than in experiments performed before 1980, while snail survival at day 30 postexposure showed insignificant differences. In bimiracidial infections, snail survival in two snail groups was significantly lower in 2006 than in experiments performed from 1981 to 1990, while insignificant differences were found for the other two populations of G. truncatula. Compared to results found between 1981 and 1990, the prevalence of snail infection did not significantly differ in 2006. In each population considered alone, the mean number of cercariae shed by infected snails did not significantly vary, whatever the date of experiment and the number of miracidia used for each exposure. The greater infectivity of F. hepatica miracidia towards snails might be the consequence of specific molecules such as triclabendazole used since 1990 to treat fasciolosis in cattle from central France.

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.

Habitats of Bulinus truncatus and Planorbarius metidjensis, the intermediate hosts of urinary schistosomosis, under a semiarid or an arid climate

Since Bulinus truncatus and Planorbarius metidjensis are the intermediate hosts of Schistosoma haematobium in southwestern Morocco, five rivers were investigated to identify sites colonized by either of both species and determine the characteristics of their habitats via the study of 12 physicochemical parameters in running water. P. metidjensis was observed in the upper valleys of three rivers, whereas B. truncatus was found in sites of lower altitude. A component analysis demonstrated that altitude (from 4 to 1,380 m), water pH (from 5.9 to 9.2), and electric conductivity (from 120 to 6,020 microS/cm) were the main descriptors of environment. A multiple correspondence analysis showed that P. metidjensis was associated to Ancylus fluviatilis, high altitude, and possibly low electric conductivity. B. truncatus was associated to Melanoides tuberculata and was found in lower altitude sites with medium electric conductivity in water. Using logistic regressions, the main characteristics were altitude and dissolved oxygen for B. truncatus, and chlorides and CaCO3 for P. metidjensis. As the habitats of both S. haematobium intermediate hosts differed from each other by altitude and the frequency of snails, which cohabited with them, these findings may be used to detect the presence of either of both intermediate hosts in numerous spring heads which are present on the western slope of the Anti Atlas mountains and the corresponding valleys.

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.

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.

The populations of Galba truncatula, known for their natural infections with Haplometra cylindracea (Digenea, Plagiorchioidea), are better intermediate hosts for metacercarial production of Fasciola hepatica

Laboratory investigations on Galba truncatula were carried out to determine if snails coming from four populations known to be natural intermediate hosts of Haplometra cylindracea, a digenean species of frogs, would not be better hosts for experimental infections with Fasciola hepatica than those originating from two communities in which H. cylindracea was never found in the past years. Uninfected G. truncatula were used to constitute six groups of snails (one per population) before being subjected to individual monomiracidial exposures with F. hepatica. Insignificant differences between mean values were noted for snail survival at day 30 post-exposure, prevalence of snail infection with F. hepatica, and prepatent period. In contrast, the duration of cercarial shedding and the number of F. hepatica cercariae in the four groups known for natural infections with H. cylindracea were significantly greater. The use of these last lymnaeid populations for experimental infections with F. hepatica allows to have high numbers of cercariae because of long patent periods and, as a consequence, strongly reduces the cost price of these larvae for scientific purposes and/or commercial production.

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.

Cercarial production of Fascioloides magna in the snail Galba truncatula (Gastropoda: Lymnaeidae)

Single-miracidium infections of Fascioloides magna in two populations of Galba truncatula were carried out under laboratory conditions to count free rediae and cercariae in snail cadavers just after death. Cercaria-shedding snails were in low numbers, and their shell height at day 60 p.e. was significantly greater than that of numerous infected snails that died without cercarial shedding. In snails that died between days 44 and 60 p.e. (at 20 degrees C), the numbers of second-generation rediae significantly increased with increasing shell heights of infected snails. First-generation rediae showed insignificant, quantitative variations, while scarce rediae of the third generation were only found in the highest snails. Cercariae were only produced by the second redial generation. In both groups of snails, free cercariae appeared from 6 mm of shell height, and their numbers increased in the upper classes up to 32.9 per snail. Metacercariae were only found from 9 mm of shell height and were in low numbers. The global cercarial production ranged from 163.5 to 210.0 in the highest classes of snail size from both groups and was limited, whereas the mean burdens of free rediae fluctuated from 39.5 to 43.9. The death of numerous infected snails without cercarial shedding might be explained by the presence of a very high number of second-generation rediae simultaneously growing within the body of these snails.

A 6- to 8-day periodicity in cercarial shedding occurred in some Galba truncatula experimentally infected with Fasciola hepatica

A retrospective study on a total of 669 Galba truncatula (three groups) experimentally infected with Fasciola hepatica was carried out to determine why 6- to 8-day interwave intervals, separating the successive waves of cercarial shedding, occurred with a regular pattern in some snails during the whole patent period. In the three groups of snails, the number of cercariae per shedding wave peaked at the second wave and subsequently decreased up to the fifth wave. The mean length of interwave intervals ranged from 6.8 to 7.8 days and only showed insignificant variations. The number of free cercariae recorded at the end of each interwave interval significantly decreased over the patent period. Similar findings were also noted for intraredial cercariae in the first redial generation and the first cohort of the second generation. By contrast, the number of intraredial cercariae significantly increased along the patent period from the second interwave interval. In the case of each interval separately considered, most numerical variations noted for free cercariae or for intraredial cercariae were insignificant. The periodicity of 6.8-7.8 days found for interwave intervals in the present study might correspond to the infradian-type rhythm already reported for the cercarial shedding of F. hepatica. However, snails showing such regular pattern in cercarial shedding along the patent period were few in number, and one may wonder about the reasons of such snails in the case of F. hepatica.

First studies on the susceptibility of Omphiscola glabra (Gastropoda: Lymnaeidae) from central France to Fascioloides magna

Experimental infections of Omphiscola glabra (preadult snails), originating from central France, to a Czech isolate of Fascioloides magna miracidia were carried out to determine if the local populations of O. glabra may ensure the larval development of this parasite and to compare these results with those noted for a natural snail host, Galba truncatula. The presence of experimentally infected snails was noted in the six populations of snails studied. However, only a few snails shed their cercariae (O. glabra 5.3 to 17.1%, G. truncatula 15.1% in the first population, and no shedding in the other). The shell heights of cercariae-shedding (CS) snails were significantly greater than those of other infected snails, for O. glabra as well as for G. truncatula. The number of metacercariae noted in each snail group was low and showed insignificant variations. When experimental infections of O. glabra were performed in relation to the shell height of snails (from 1 to 14 mm) at miracidial exposure, the prevalence of infected snails significantly decreased with increasing shell heights at exposure. However, the presence of CS snails was only noted from the 5-6 to the 9-10 mm groups, and the mean number of metacercariae per group ranged from 27 to 44.2. Despite the high infectivity of the Czech isolate of F. magna miracidia, there was an incomplete adaptation with the French G. truncatula and O. glabra used in this study, as the metacercarial production was low, and cercarial shedding only occurred for snails which showed a strong increase of their shell height during F. magna infections.

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.

The contamination of wild watercress with Fasciola hepatica in central France depends on the ability of several lymnaeid snails to migrate upstream towards the beds

As most natural watercress beds in central France are located upstream of the permanent habitats of two lymnaeid species, Galba truncatula and Omphiscola glabra, field investigations were made from 1999 to 2004 on 67 beds to determine why the contamination of watercress with Fasciola hepatica is irregular over time in these sites, while definitive hosts, especially lagomorphs, are regularly found infected around them. Snails are able to migrate upstream in winter and spring towards the beds, and a 4-year survey demonstrated the existence of annual variation in the colonization of these sites by snails. In the 45 beds irregularly contaminated with F. hepatica over time, 37.7-62.2%, according to the year, were not populated by lymnaeids, in spite of the presence of snail populations downstream. G. truncatula was found alone in 8.8-13.3% of sites and was the first colonizing snail in 24.3-33.3% when the two lymnaeid species successively settled in these waterholes. The colonizing ability of O. glabra was more limited, as it was observed alone in 2.2% of beds and was the first colonizing snail in only 2.2-20% of them. The distances covered by these snails significantly increased with increasing migration time. After migration, a few overwintering snails (3.8% of G. truncatula and 6.8% of O. glabra) are able to colonize the beds, but their numbers decreased when the distance of migration was greater. O. glabra migrated more quickly and reached more watercress beds than G. truncatula. However, this did not influence the natural infections of snails, which were more frequent in the F1 of G. truncatula. The variability observed in the colonization of beds by snails might explain the regular or irregular contamination of wild watercress by metacercariae of F. hepatica. One of the factors which may explain this variability is the occurrence of showers in spring, so that a few snails are able to reach watercress beds after their upstream migration.

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.