The epidemiology and impact of hydatid disease (Echinococcus granulosus) in beef cattle in eastern Australia

The overall objective of this thesis was to determine the importance of hydatid disease to the Australian beef industry and to gain a deeper epidemiological understanding of this disease. In doing so, the diagnostic accuracy of routine meat inspection for hepatic hydatid disease was estimated and the burden of hydatid disease in individual cattle was investigated. Apparent and true prevalence of hydatid disease in beef cattle were estimated and risk factors associated with infection identified. Direct economic losses associated with hydatid disease were estimated and the knowledge, attitudes and practices of Australian beef producers was described. Routine post-mortem meat inspection at an eastern Australian abattoir (the ‘focus abattoir’) for hepatic hydatid disease was found to have a very low sensitivity (24.9%), but a very high specificity (98.9%). The low sensitivity of routine meat inspection indicated that prevalence reported by the abattoir was underestimated, but the high specificity indicated that truly uninfected livers were generally correctly reported. The sensitivity of routine meat inspection was higher with a greater number of cysts. Burden (number and size) of cysts in individual cattle had not changed since previous studies. Cattle typically had few and small cysts, but the size and number of cysts were positively correlated with dentition (age) of the animal. A retrospective study using data from 2010 to 2018 on 1,178,329 cattle slaughtered at the focus abattoir was conducted. Apparent prevalence of hydatid disease using the abattoir data was 8.8% (95% confidence interval [CI] 8.8–8.9%). However, when accounting for sensitivity and specificity of routine meat inspection, true prevalence, was estimated to be 33.0% (95% CI 24.4–44.4%), which is higher than previously recognised. The identification of infected cattle in almost all sampled regions demonstrated that the geographic distribution of hydatid-infected cattle is also wider than previously thought. Multilevel regression showed that the odds of hydatid disease were highest in eight-tooth cattle (>42 months) and cattle that were grass-fed. The median estimated direct loss to the focus abattoir between 2011 and 2017 was AU$655,560 (95% CI AU$544,366–787,235). This equated to approximately AU$6.70 (95% CI AU$5.56–8.05) lost per infected animal. This estimate is most likely an underestimate, therefore, these losses indicate that hydatid disease has a substantial economic impact on the Australian beef industry. The knowledge, attitudes and practices survey demonstrated that knowledge of hydatid disease among beef producers, and their attitudes towards the disease are associated with practices that could influence transmission of Echinococcus granulosus. The study also demonstrated that improving knowledge and awareness of hydatid disease among beef producers is required and would be well received by beef producers.These results demonstrate that abattoir data should be validated prior to being used in epidemiological studies, and the accuracy of abattoir data collection needs to be improved to facilitate both surveillance and research. It is likely that results from these studies are generalisable to the entire beef cattle population of eastern Australia due to the wide geographic catchment of the focus abattoir, the large study population, and the long duration of data collection. However, further studies to estimate the prevalence and economic losses in other beef abattoirs are required to determine this and support development of further control strategies (such as vaccination to prevent hydatid infection). Hydatid disease in beef cattle has important epidemiological and economic impacts on the Australian beef industry. Improved knowledge and awareness of hydatid disease among Australian beef producers is required, and practical and cost-effective control measures need to be identified.