Response of sheep to challenge infection with Fasciola hepatica

Sheep were infected with 100 metacercariae of Fasciola hepatica and reinfected 16 weeks later with a further 100 metacercariae. Serum samples were taken weekly for 36 weeks after primary infection. Serum was assayed for the presence of the enzymes glutamate dehydrogenase (GLDH) and gamma-glutamyl transferase (gamma-GT), as indicators of liver and bile duct damage respectively, and for levels of precipitating antibody. Antibody and GLDH levels rose following the primary infection but fell after patency had been reached . A peak in gamma-GT activity was associated with the onset of patency. After the challenge infection levels of both enzymes rose substantially and there were persistent fluctuations in activity. Antibody levels did not rise markedly following challenge but fluctuated at low levels until autopsy, 20 weeks after challenge. There was no resistance to challenge judged by worm recoveries at autopsy. It is suggested that the presence of adult flukes in the bile ducts suppresses the antibody response to challenge infection. Tissue damage, which is shown by fluctuations in GLDH and gamma-GT levels after adult flukes have become established in the bile ducts, is considered to be due to the feeding activity of adult flukes and the deposition of immune complexes in the liver parenchyma.     

Responses of Fasciola hepatica infected sheep to various infection levels

The response to Fasciola hepatica was studied in sheep infected with 5, 30, 150 metacercariae. The animals were necropsied 12 weeks post-infection (p-i) for counting and measuring flukes. Cellular and humoral responses were detected by peripheral eosinophil count, peripheral blood lymphocyte proliferation with excretory-secretory products (FhESP) and ELISA. All sheep were infected at necropsy except one sheep which was infected with 5 metacercariae. Mean parasitic intensities were 40%, 44% and 27% of the infection dose in sheep infected with 5, 30, 150 metacercariae respectively. FhESP-specific lymphocyte responses of the 3 infected groups were significantly enhanced in weeks 3 and 4 p-i (p < 0.05). The kinetics of the specific humoral response were similar for the 3 infected groups but the antibody level was significantly lower in animals infected with 5 metacercariae than in the 2 other infected groups from week 5 p-i to week 12 p-i (p < 0.05). Peripheral eosinophil count was significantly enhanced (p < 0.05) in infected groups. The numbers of peripheral eosinophils were significantly different between the 3 infected groups in week 3, 4 and 6 p-i and were related to infection level. These results confirm that sheep are highly susceptible to F. hepatica infection, even when infection pressure is very low. Peripheral eosinophilia was dependent of the infection level. The immune response was similar in sheep infected with various numbers of flukes.     

Diagnosis of Fasciola hepatica infection in beef calves by plasma enzyme analysis

Plasma analysis for albumin, total bilirubin, and total protein values and aspartate aminotransferase (AST), arginase, and gamma-glutamyl transpeptidase (GGT) activities was used for the early and quantitative diagnosis of experimental Fasciola hepatica infections in beef calves. Calves were infected on 3 occasions with 1,000 (n = 5), 100 (n = 5), or 10 (n = 4) metacercariae for a total infective dose of 3,000, 300, or 30, respectively. Albendazole (15 mg/kg of body weight) was administered to 7 infected calves on postinfection (initial) week (PIW) 13. All calves were euthanatized and necropsied on PIW 16 for the determination of fluke infections. Plasma constituents were determined weekly. Significant (P less than 0.05) increases in AST activity occurred as early as PIW 4 and GGT activity at PIW 9, as compared with that in noninfected controls. Fluke burden-related differences were observed in GGT activity from PIW 9 onward. Increases in AST activity reflected parenchymal liver damage, whereas increases in GGT reflected hepatobiliary damage; therefore, differentiation could be made between the migratory and ductal phases of the infection. There was no correlation between arginase activity and fluke infection. As compared with fecal examination results, plasma enzyme analysis gave an earlier and semiquantitative indication of F hepatica infection in experimentally infected calves. Although increases in these plasma constituents were not definitely diagnostic of fascioliasis, useful information on the size of the fluke burden and progress of the disease process could be obtained by these methods. Plasma enzyme analyses of AST and GGT were not indicative of chemotherapeutic success or failure when calves with mature F hepatica (14 weeks old) infections were treated.     

Diagnosis and economic consequences of triclabendazole resistance in Fasciola hepatica in a sheep flock in south-east Scotland

Over the past decade, definite changes have been recorded in the regional prevalence, seasonality and severity of fasciolosis in the UK, related to increased rainfall, or localised flooding, prompting debate about the deleterious effects of climate change. As a consequence, effective management of fasciolosis has become problematic in areas where fluke traditionally exists, leading to serious loss of production in sheep and cattle. Meanwhile, in eastern districts, there have been unexpected outbreaks of disease, resulting in production losses and concerns about welfare. This case report describes the economic consequences of fasciolosis in a commercial sheep flock in south-east Scotland. The diagnosis and consequences of triclabendazole resistance are discussed, in the context of developing economically sustainable control strategies.     

The serum glucose and beta-hydroxybutyrate levels in sheep with experimental Fasciola hepatica and Fasciola gigantica infection

The influence of Fasciola hepatica and Fasciola gigantica infection on serum glucose and beta-hydroxybutyrate (beta-HOB) in sheep was evaluated. This was done by setting up two groups of sheep. The first group (n=13) was split in two sub-groups, one experimentally infected with F. hepatica (n=9) and the other (n=4) as uninfected control. A second group consisting of a sub-group experimentally infected with F. gigantica (n=9) the other sub-group (n=6) left as uninfected control was also set up. The results of weight gain, parasitological and serum liver enzymes activity (glutamate dehydrogenase [GLDH] and gamma glutamyltransferase [gamma-GT]) used in monitoring the infection showed that all infected animals developed fasciolosis. It was observed that a reduction in serum glucose levels was significantly lower (p<0.05) in F. hepatica infected sheep than in uninfected control sheep starting from 5 weeks post-infection (wpi) to the end of the experiment. Similar reduction was recorded in F. gigantica infected sheep between 8 and 19 wpi. In contrast, serum beta-HOB levels were elevated in F. hepatica infected sheep between 6 and 16 wpi and in F. gigantica infected sheep between 7 and 15 wpi. It would appear from these serum glucose and beta-HOB levels that fasciolosis does lead to energy deficiency (low glucose) and ketosis (increased beta-HOB). The decrease in serum glucose and increase in serum beta-HOB levels in infected sheep may help in understanding the interaction between fasciolosis and nutritional status of infected ruminants especially in young growing animals.     

The effect of Taenia hydatigena infection on existing and concurrent infections of Fasciola hepatica in sheep

Sheep given a primary infection of Fasciola hepatica were challenged 18 weeks later with Taenia hydatigena or F hepatica, or both parasites together, or were not challenged. At the same time, control sheep were infected with T hydatigena and/or F hepatica separately or concurrently. All sheep were killed seven weeks after challenge and the number of cysts and flukes counted. Challenge infection with T hydatigena did not affect the numbers of flukes recovered from either primary or challenge F hepatica infections. On the other hand, the numbers of cysticerci were reduced in sheep previously infected with F hepatica but not in those given T hydatigena and F hepatica concurrently.     

Galectin secretion and binding to adult Fasciola hepatica during chronic liver fluke infection of sheep

Galectins are increasingly recognised as important mediators of immune homeostasis and disease regulation, but comparatively little is known about their role in parasite infection. This study investigates the interaction between two ovine galectins, galectin-11 and galectin-14, and the parasitic liver fluke, F. hepatica. Galectin-14 was found in eosinophils infiltrating the tissue surrounding infected bile ducts and secreted in the connective tissue, while galectin-11 was specifically induced in epithelial cells of bile ducts from infected sheep. Strong nuclear staining was observed for galectin-11. Both galectins were found to be secreted into the bile fluid of parasite infected sheep, and were also detected in the excretory/secretory products of adult flukes, following their removal from the ovine host. Recombinant galectin-14, but not recombinant galectin-11, was found to bind specifically to the surface tegument of adult flukes in a carbohydrate dependent manner. This study shows for the first time that both galectin-14 and galectin-11 are produced in liver tissue after chronic liver fluke infection and that they can directly interact with the parasite in the bile ducts. Galectin-11 may also be involved in epithelial cell turnover and cancerogenesis.     

Comparison of different Fasciola hepatica antigens and their use to detect infection in sheep by an enzyme immunoassay

Soluble antigens of adult Fasciola hepatica were extracted from homogenized parasites and purified with gel chromatography on Sephadex G-200. Six peaks were obtained, and the second highest in molecular weight showed highest correspondence in a microplate enzyme immuno assay with parasite metabolite antigens. Optimal coating antigen concentration was 5 micrograms/ml and sample dilution 1:20. Total running time of assay was 3 hours. Positive and negative sheep sera was obtained from a group of experimentally infected tracer lambs.