The Epidemiology and Control of Caseous Lymphadenitis in Australian Sheep Flocks

The objective of this thesis was to better understand the epidemiology of caseous lymphadenitis (CLA) and its economic effects on the Australian sheep industries. The work also sought to apply this knowledge to better understand how to control the disease in Australian sheep flocks. The occurrence of CLA in some other species, as a comparison to CLA in sheep, is described in the literature review. However a comprehensive review of research on CLA in all livestock species is not needed to meet the aims of the thesis. The research used serological tests developed in the 1970s and ‘80s to examine the epidemiology and costs of CLA in Western Australian sheep flocks. Epidemiological techniques were used to determine the main risk factors associated with high incidences of CLA. Controlled experimentation was used to better understand the spread of CLA within flocks. Prevalence data collected at abattoirs and survey techniques were employed to better understand how CLA was being controlled in Australian sheep flocks. It was shown that toxin and cell wall ELISA tests for CLA were useful tools to study the spread of CLA in sheep flocks. Using the serological tests it was estimated that 80 per cent of CLA spread occurs after the second and third shearings. This knowledge was used to design a risk factor study which identified two significant factors associated with high CLA spread, that is in dips and close contact after shearing. These tests also facilitated the study of new CLA infection on wool production. It was found that sheep produce approximately five per cent less clean wool in the year in which they are infected.