title: Does Fasciola hepatica infection increase the susceptibility of cattle to infection with other pathogens normally controlled by a Th1 or pro-inflammatory response?
Creators: name: Claridge, Jennifer
Publisher: name: University of Liverpool Repository
Year: 2013

description: Fasciola hepatica is a trematode parasite with wide geographical and host ranges, primarily affecting ruminants in the United Kingdom. Infection of host animals leads to significant economic losses in production, with reduced weight gains and milk quality and quantity. Clinical disease, known as fasciolosis, is expensive to treat and causes significant morbidity and mortality. More than three quarters of dairy herds surveyed in England and Wales have been exposed to this parasite, and the number of diagnoses of fasciolosis, made by the Animal Health Veterinary Laboratories Agency, has increased dramatically in the last fifteen years. Experimental studies have demonstrated failure to diagnose bovine tuberculosis (BTB) when co-infection with F. hepatica is present. In Chapter 2, we demonstrate a novel method for estimating the prevalence of BTB in England and Wales and show that, in light of the imperfect diagnostic test for BTB, the prevalence may be significantly higher than currently reported. In Chapter 3, a logistic regression model for the presence or absence of BTB on farms in England and Wales is designed, based upon those previously published. The addition of a variable to describe the burden of F. hepatica found in the locality of each farm significantly increases the predictive power of the model and may help to explain the under-diagnosis of BTB suggested in Chapter 2. A significant, negative association is demonstrated between F. hepatica exposure and the BTB status of the farm. The difference between the model predictions for BTB status made with F. hepatica exposure as tested and the predictions made assuming F. hepatica exposure is negative is then calculated to provide an estimate of the missing BTB diagnoses due to co-infection. We show this under-ascertainment to be over one third of cases. The significant, negative association between F. hepatica exposure and BTB diagnosis described at the herd level in Chapter 3, is then tested on an animal level. In Chapter 4, milk samples from individual animals testing negative and inconclusive, or negative and positive to the BTB test are assessed using the anti-F. hepatica antibody ELISA and an exposure value obtained. Significantly higher exposure to F. hepatica was not found in either pairing of BTB outcome-cattle and potential reasons for this are discussed. Chapter 5 investigates the association between F. hepatica exposure and other infectious diseases such as Bovine Viral Diarrhoea virus (BVDv), Leptospira spp, Infectious Bovine Rhinotracheitis, Johnes Disease and Neospora caninum. A random effects model is constructed using information collected about animal and farm parameters, to predict F. hepatica exposure. Vaccination against BVDv and Leptospira spp are shown to be significantly associated, the former being positively and the latter being negatively correlated. Johnes Disease prevalence is negatively associated with F. hepatica exposure and Salmonella Dublin prevalence is positively associated. Farm management and husbandry variables were also found to be significantly associated with F. hepatica exposure. In total, this thesis adds to the growing realisation that co-infection with this pathogen can have significant repercussions on the diagnostic ability of the BTB test and on the health and welfare of the national herd.