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    Assessment of accuracy of liver fluke diagnostic tests using the gold standard of total worm counts.
    (Elsevier B.V., 2024-08-24) Dowling A; Lawrence KE; Howe L; Scott I; Pomroy WE
    In many regions of New Zealand liver fluke is endemic, infecting most grazing ruminants, including cattle, sheep, and deer. Restricting the economic losses and welfare costs associated with liver fluke relies on accurately identifying those animals with a production limiting infection. This has proven a difficult goal and although several antemortem quantitative tests are available, including faecal egg counts (FEC), serum ELISA and copro-antigen ELISA, none can be considered a gold standard test of liver fluke infection. The accepted gold standard test for fascioliasis is the total fluke count, which is both laborious and can only be completed at post-mortem. This study aimed to compare the performance of four liver fluke diagnostic tests, against the results of a gold standard total fluke count test. Two groups of cattle were selected, 29 culled mixed age beef cows (MAC) and ten 30-month-old steers. The cattle were blood sampled and faecal sampled prior to slaughter and their whole livers recovered post slaughter at the abattoir. Liveweight was also recorded at slaughter. After collection, each liver was weighed, scored for gross pathology, then serum, faeces and livers were frozen at -20 °C for later analysis. Faecal egg counts and F. hepatica copro-antigen ELISA tests were completed on the faecal samples and total fluke counts were completed on the livers. Fasciola hepatica antibody concentration in serum samples were quantified using a commercial ELISA test. Poisson regression models were built to model the association between each diagnostic test and the total fluke count, and a linear regression model was built to examine the relationship between each diagnostic test and live weight at slaughter. The median fluke count was significantly higher in MAC than steers (p = 0.01), and F. hepatica eggs were present in 100% steers and 66% MAC. There was a significant effect of copro-antigen ELISA value on total fluke count (p < 0.0001), with a coproantigen ELISA value = 20.1 predicting 10 flukes and a value = 44.8 predicting 30 flukes. There was also a significant effect of FEC on total fluke count (p = 0.002) but the R-squared value for this model was lower. There was no association between liver fibrosis score or antibody ELISA test and total fluke count (p = 0.95, p = 0.73, respectively). There was a significant effect of total fluke count (p = 0.03) on liveweight at slaughter, with liveweight falling 20.4 kg for each unit increase in loge (total fluke count). There was no effect of FEC (p = 0.11), antibody ELISA (p = 0.55) or copro-antigen ELISA value (p = 0.16) on liveweight at slaughter. Taken together, these results show that the coproantigen ELISA test is the better test for estimating the true liver fluke burden and that the number of flukes in the liver has a negative effect on cattle live weights at slaughter.
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    Comparative study of subclinical fascioliasis in sheep and goats : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy in Veterinary Science at Massey University
    (Massey University, 1991) Mengesha, Kinfe Melak
    The literature on the identification of Fasciola spp. and their intermediate hosts, the general life cycle of Fasciola and aspects of the epidemiology, clinical signs, diagnosis and treatment of infections is reviewed. Two experiments were carried out. The first involved 18 weeks observations on 5 adult male goats each infected with 150 metacercartae of F.hepatica and 5 uninfected controls. The second involved groups of 10 sheep and 10 goats each infected with 200 metacercariae with 5 uninfected controls of each species. In both experiments, faecal, haematological, biochemical and pathological examinations were conducted. The animals were also weighed regularly. In the first experiment, although only 15-35 flukes were established, measurable and, in many cases, statistically significant changes in a variety of parameters were observed. A depression in packed cell volumes relative to controls of approximately 20% occurred. Though haemoglobin, mean corpuscular volume and mean corpuscular haemoglobin concentration levels remained within the normal ranges, erythrocyte levels in the infected group were significantly lower than in the controls and there was a tendency for the anaemia to become macrocytic. This suggests that goats may be particularly susceptible to the effects of blood loss associated with Fasciola infections though further work is needed to confirm this. A marked peripheral eosinophilia and elevation in fibrinogen levels were observed in infected animals. Albumin levels decreased, globulin levels increased and the A/G ratio decreased significantly relative to the control group but all levels remained within the normal ranges. In infected animals, gamma glutamyl transferase (GGT) and glutamyl dehydrogenase (GD) levels rose to beyond the limits of the normal ranges although aspartate aminotransferase (AST) levels, which were also significantly elevated, did not. The results indicate that serum GD and GGT are particularly sensitive indicators of damage to the liver parenchyma and bile ducts caused by F.hepatica in goats and that GD is more sensitive than AST. Serum bile acids were estimated but no significant change was detected. The ratio between faecal egg counts and the numbers of adult flukes present at necropsy was consistently lower than described for sheep with a mean of approximately 13epg/fluke (range 9-23) at the final sampling and 18epg/fluke (range 11-29) in the previous week when the egg counts were highest. This is potentially of considerable diagnostic importance and needs further investigation. In the second experiment, the number of flukes established was extremely low in both species (mean 0.85% & 2.95% in the sheep and goats respectively) although more goats than sheep became infected. Pre-existing liver pathology in the sheep was a further complication. Consequently, little information of value was generated by the infection of goats and no data that could be used for comparative purposes were obtained from the sheep infection. However, combination of the data from the 13 infected goats from both experiments yielded some useful information in relation to serum enzyme levels. Correlations between the numbers of flukes recovered at necropsy and peak levels of serum enzymes and various haematological parameters in individual animals were examined though only those relating to enzyme levels were statistically significant. The correlation coefficients between peak enzyme levels and fluke numbers indicated that the relationship was strongest with GGT and weakest with AST. However, regression analysis showed that there was no predictive value in the relationship with any of the enzymes because of extremely wide confidence intervals for predicted fluke numbers.