Study of lesser virulent footrot in NSW
Karen Smith, Richard Whittington, Navneet Dhand and Om Dhungyel
Sydney School of Veterinary Science, The University of Sydney
Posted Flock & Herd September 2021
Footrot is a contagious disease that affects the welfare of animals and causes production losses in the sheep meat and wool industries worldwide. The Gram-negative bacterium Dichelobacter nodosus is the essential causative agent of ovine footrot and can cause a spectrum of disease ranging from benign to virulent footrot which results in severe lesions with under-running of the hoof. The prevalence of disease is influenced by host susceptibility, virulence of isolate and environmental conditions, with higher levels of disease typically occurring in warm and moist climatic conditions. The prevalence of virulent footrot has been reduced to <1% of flocks in New South Wales (NSW) due to the implementation of the Footrot strategic Plan in 1988. Consequently, the impact of lesser virulent strains of D. nodosus is becoming more apparent in NSW with traditional treatments and eradication programs often failing to eliminate the disease. In my research project studies at the University of Sydney I have looked at the following aspects of the disease relating to NSW:
- The pathogenicity of field isolates was examined in a pen trial to investigate whether a PCR test developed in Europe to determine the virulence of D. nodosus would be accurate and applicable to Australian isolates and also whether these lesser virulent forms of the disease would be eradicable by the application of appropriate treatments.
- The feasibility of pooling samples to improve the efficiency and cost effectiveness of diagnostic testing using PCR assays was assessed using foot swab samples collected from sheep farms in Tasmania and New South Wales (NSW).
- A vaccine trial was conducted at four farms in NSW diagnosed with benign or lesser virulent forms of footrot. The aim of the trial was to determine the efficacy of a serogroup-specific bivalent footrot vaccines against the lesser virulent forms of the disease.
- A study examining the gene expression was conducted to develop a greater understanding of virulence factors. Several genes and virulence factors of D. nodosus have been identified and the expression of some of these virulence related genes in isolates cultured in variable environmental conditions were studied.
- A survey study was conducted to identify risk factors associated with footrot and other hoof diseases in NSW and also to develop an understanding of farmer knowledge and attitudes regarding foot and hoof diseases. In addition, a second survey study aimed at veterinarians and animal health officials working with the sheep industry in NSW was conducted to better understand the services provided.
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