Browsing by Author "Dowling A"

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    Prevalence of liver fluke on West Coast farms of the South Island of New Zealand sampled in the autumn and spring of consecutive lactations
    (2021-07-19) Dowling A; Pomroy W; Howe L; Scott I; Lawrence K
    The aim of this study was to determine the occurrence of Fasciola hepatica infection in dairy cows in this West Coast of the South Island using an ELISA of bulk milk samples (n=430) collected on one of two occasions during March (autumn) 2017 and again in October (spring). All samples were analysed using the IDEXX Fasciolosis Verification kit which estimates the infection level in the herd in 4 categories; >50% infestation (strong); 20-50% infestation (medium); <20% infestation (low); no infection. A subset (n=99) were tested twice with a one week interval to determine repeatability. A short survey was also posted to each supplier with 157 completed. Of the 430 farms tested 133 (31%) were negative, 49 (11%) had a low infestation, 62 (14%) had a medium infestation and 186 (43%) had a strong infestation. GIS mapping of the farm locations indicated geographic grouping of farms with more severe fluke infestations. The 99 samples tested twice substantially agreed (Kappa = 0.7). Farms tested in both autumn and spring (n= 369) moderately agreed (Kappa 0.43) with an overall decrease in the spring. From the survey 85% of farmers were aware of liver fluke on their farm during the last 5 years and 70% treated their cows with a flukicide during the dry period (winter) including 92% of the farms that tested negative. This study indicates fasciolosis is common in this region with a disturbing number with a high prevalence in their herds. It also showed a decrease from autumn to following spring levels.
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    The use of a Bayesian latent class model to estimate the test characteristics of three liver fluke diagnostic tests under New Zealand field conditions.
    (2024-09-12) Dowling A; Lawrence KE; Scott I; Howe L; Pomroy WE
    The liver fluke Fasciola hepatica is a trematode parasite of farmed livestock with worldwide distribution, causing chronic production losses and possible death from hepatobiliary damage. The effective management of liver fluke infection requires diagnostic tests which can accurately identify infected animals at both the individual and herd level. However, the accuracy of liver fluke diagnostic tests performed on individual New Zealand cattle is currently unknown. The aim of this study was to use a Bayesian latent class model (LCM) to estimate the test characteristics of three liver fluke diagnostic tests, the coproantigen ELISA, the IDEXX antibody ELISA and the faecal egg count. One hundred and twenty dairy cows each from two dairy farms were blood and faecal sampled in April 2021. The samples were transported to Massey University, Palmerston North, and the three diagnostic tests completed following the respective manufacturer instructions. A Bayesian LCM model, adapted from the original Hui and Walter 2 tests 2 populations model, was built to estimate the test characteristics of the three diagnostic tests in the two dairy herds. The model was implemented in JAGS using Markov chain Monte Carlo sampling. The first 30,000 iterations were discarded as burn-in, and the next 200,000 iterations were used to construct the posterior distributions. Uninformed priors, beta (1,1), were used as the prior distributions for the prevalence estimation and informed beta priors, based on published results, were used as the prior distributions for estimating the sensitivity and specificity of each diagnostic test. Model convergence was confirmed by inspection of trace plots and examination of the results of the Gelman and Rubin test. The results found that the coproantigen ELISA test was the most accurate for diagnosing liver fluke infection in individual animals with a sensitivity = 0.98 (95 % CI 0.95-1.00) and specificity = 0.95 (95 % CI 0.81-1.00) compared to the IDEXX antibody ELISA test, sensitivity = 0.39 (95 % CI 0.32-0.47) and specificity = 0.86 (95 % CI 0.75-0.96) or the FEC, sensitivity = 0.23 (95 % CI 0.17-0.30) and specificity = 0.92 (95 % CI 0.86-0.97). Based on these results clinicians should be encouraged to use the coproantigen ELISA test to diagnose liver fluke infection in individual cattle.