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

The Differences in the Susceptibility Patterns to Triclabendazole Sulfoxide in Field Isolates of Fasciola hepatica Are Associated with Geographic, Seasonal, and Morphometric Variations

Triclabendazole (TCBZ) resistance is an emerging problem in fascioliasis that is not well understood. Studies including small numbers of parasites fail to capture the complexity of susceptibility variations between and within Fasciolahepatica populations. As the first step to studying the complex resistant phenotype−genotype associations, we characterized a large sample of adult F. hepatica with diverging TCBZ susceptibility. We collected parasites from naturally infected livestock slaughtered in the Cusco and Cajamarca regions of Peru. These parasites were exposed to TCBZ sulfoxide (TCBZ.SO) in vitro to determine their susceptibility. We used a motility score to determine the parasite’s viability. We titrated drug concentrations and times to detect 20% non-viable (susceptible conditions) or 80% non-viable (resistant conditions) parasites. We exposed 3348 fully motile parasites to susceptible (n = 1565) or resistant (n = 1783) conditions. Three hundred and forty-one (21.8%) were classified as susceptible and 462 (25.9%) were classified as resistant. More resistant parasites were found in Cusco than in Cajamarca (p < 0.001). Resistant parasites varied by slaughterhouse (p < 0.001), month of the year (p = 0.008), fluke length (p = 0.016), and year of collection (p < 0.001). The in vitro susceptibility to TCBZ.SO in wildtype F. hepatica was associated with geography, season, and morphometry.

Endemic occurrence of Fasciola hepatica in an alpine ecosystem, Pyrenees, Northeastern Spain

Fasciola hepatica is a liver parasite of ruminants whose distribution is determined by its intermediate host, the freshwater snail Galba truncatula. In Europe, F. hepatica is mostly associated with lowlands. Infection from sympatric domestic reservoirs is rarely reported in wild mountain ungulates. This study explores F. hepatica in a multi-host system in a European alpine area. Serum samples (n = 1,209) from Pyrenean chamois (Rupicapra p. pyrenaica), European mouflon (Ovis aries musimon), domestic sheep (Ovis aries) and domestic cattle (Bos taurus) were collected in the National Game Reserve of Freser-Setcases (NGRFS) in Catalonia, Northeastern Spain, from 2008 to 2019, and tested for antibodies against F. hepatica. During the same period, the livers of 214 chamois hunted in the NGRFS were inspected for F. hepatica and associated pathological changes. Finally, 907 freshwater snails were collected in summer 2016 between 1559 and 2,224 metres above sea level (asl) in the NGRFS, and F. hepatica DNA sought by PCR. Antibodies against F. hepatica were detected in all four species, with a higher prevalence in cattle and sheep than in chamois. Fasciola hepatica and hepatic lesions were concurrently observed in 13/214 of the chamois livers inspected (6.1%, CI95 2.9%-9.3%). Fasciola hepatica DNA was detected in one out of the 907 snails (0.1%, Cl95 0.1% - 0.3%; Ct value 33.3) and collected at 2054 m asl. Fasciola hepatica was consistently detected in a high mountain multi-host system, suggesting that its life cycle is completed and that it occurs endemically at the highest elevation reported in Europe. Transhumant livestock are the likely source in this alpine ecosystem, which according to rare occurrence of F. hepatica DNA in G. truncatula is still a suboptimal habitat for F. hepatica life cycle. Studying parasites at their highest distribution range can be useful to monitor climate change in seasonal mountain environments.

Ecological niche modeling for predicting the habitat suitability of fascioliasis based on maximum entropy model in southern Caspian Sea littoral, Iran

The present study aimed to determine the number of cases of animal fascioliasis per district in the southern littoral of Caspian Sea and to model suitable ecological niches for Fasciola infection in the region. Stool samples (n = 2688) were collected from cattle and sheep in Guilan, Mazandaran and Golestan provinces. The samples were tested using flotation method, and the number of parasite eggs per gram (EPG) of feces was recorded for each sample. Occurrence-only data of Fasciola were collected from the field. A total of 96 points/locations were used to model the ecological niche of Fasciola in maximum entropy (MaxEnt) and geographical information system (GIS). The spatial layers were compiled from 23 bioclimatic and biophysical variables for modeling analysis. Jackknife analysis was used to determine the relative importance of all variables in the model. In the present study, the proportion of fascioliasis in both hosts was highest in Guilan province (sheep: 12.34%, cattle: 15.16%), followed by Mazandaran (sheep: 7.3%, cattle: 6.25%) and Golestan (sheep: 0%, cattle: 0.94%) provinces. The Area Under Curve (AUC) value of the model was 0.909, indicating a good predictive power of the model. Our modeling results indicate that four variables, which were markedly incorporated into the model, are the major predictors of the presence probability of Fasciola spp. in the region: Bio17 (Precipitation of driest quarter; 45.5%), Bio14 (Precipitation of driest month; 24.8%), aspect (9%), and altitude (7.2%). The data presented herein show expansion of the potential high-risk areas of fascioliasis in the northern part of Iran, located at the southern littoral of Caspian Sea, especially in Guilan province. However, the extent of the predicted risk zones varied between the different areas of the region and within provinces, such that at the present, many parts of Golestan province are less environmentally suitable for Fasciola distribution than other areas in the region.

Recent developments in the epidemiology, diagnosis, and treatment of Fasciola infection

PURPOSE OF REVIEW

This review aims at describing the latest research in Fasciola epidemiology, diagnosis, treatment, and control in endemic countries.

RECENT FINDINGS

The geographic distribution and range of reservoirs for Fasciola hepatica continues to expand. The impact of fascioliasis goes beyond human disease to affect food security and income in developed and developing countries. Promising serologic and molecular methods to diagnose fascioliasis have been described, but are not widely available. Triclabendazole remains the only highly active medication to treat human and livestock infected with juvenile and adult forms of Fasciola spp. Efforts to control fascioliasis may be hindered by the emergence of resistance to triclabendazole among livestock and subsequently in humans.

SUMMARY

Increased awareness and surveillance are likely to uncover the real distribution and burden of fascioliasis in human. Research into new drugs or adjuvants to tackle the emerging resistance to triclabendazole is imperative to treat and control Fasciola infection.