John Larson - Mentor for Postdoctoral Fellow

Summary

'Weaner scours' causes scouring, illthrift and mortality in 3-16 months old Merino weaners from autumn to early spring. This syndrome, also called bacterial enteritis, causes significant economic loss and is an important animal welfare issue, with up to 80% of a mob affected during an outbreak. Affected sheep often have low worm burdens and the diarrhoea is not stopped by anthelmintic treatment ('drenching'), but does respond to treatment with antibiotics.
Based on clinical investigations, the primary infectious cause of weaner scours are Yersinia bacteria. The epidemiology of these organisms has not been investigated recently and appears to have changed, with more severe annual outbreaks on many farms. The main species are Yersinia enterocolitica and Yersinia pseudotuberculosis, both of which can cause disease in humans; these were the focus of this project.
Dr Helen McGregor was recruited as a post-doctoral candidate and responsible for the design and conduct of a 3-year study of weaner scours, from 2012-2015. She co-supervised one Honours student to completion in 2014, and one PhD student due to complete in 2016. 
Aspects studied during field trials in 5 flocks, and clinical investigations in 22 flocks, included patterns of faecal shedding, risk factors for transmission and climatic, seasonal and husbandry factors associated with disease outbreaks and shedding of Yersinia sp. A laboratory study investigated the potential environmental survival of Yersinia isolates from affected flocks.
Key outputs from this project included: 1) the establishment of a library of Yersinia isolates from over 30 affected flocks; 2) development of molecular tests for the rapid and more accurate differentiation of Yersinia sp.; 3) confirmation that Y. pseudotuberculosis is highly seasonal, being isolated from faeces only immediately before or during an outbreak, whereas Y.enterocolitica is shed throughout the year; 4) development of standardised method for assessing antibiotic sensitivity in Yersiniae, with 7% of Y.enterocolitica and 31% of Y.pseudotuberculosis showing resistance to a commonly used antibacterial class (sulphafurazole); 5) Y.pseudotuberculosis was more tolerant of low temperatures and desiccation compared to Y.enterocolitica; 6) a factor associated with virulence of Yersinia sp. was not affected by extremes of temperature or desiccation and 7) development of leadership skills of the post-doctoral candidate and comprehensive training of Honours and PhD students.