Lower-virulent footrot in NSW

Full title: Study of lower-virulent footrot in NSW

Karen Smith
University of Sydney

Summary

Ovine footrot is an endemic disease in many sheep-producing countries with Dichelobacter nodosus, an anerobic bacteria, the essential causative agent. Footrot causes production losses and lameness which can compromise animal welfare. The severity of disease which develops is on a spectrum, with benign, intermediate, and virulent forms of footrot described.

Two clinical forms of footrot are recognised in New South Wales (NSW), benign and virulent, with virulent footrot a notifiable disease in NSW. Differentiating and identifying the clinical form of disease present is challenging due to the changes in the interactions between host susceptibility, environmental conditions and the strain(s) of D. nodosus present.

The research was conducted as a PhD project which aimed to improve our understanding of various aspects of the less severe forms of footrot (benign and intermediate). A pen trial was conducted to determine the pathogenesis of three field strains of D. nodosus which were positive for the virulence gene aprV2. It was established that isolates which contained the aprV2 gene may not always cause virulent footrot.

To further understand the role of virulence genes in D. nodosus, a study examining expression of two virulence associated genes (aprV2 and pilT) in six strains of D. nodosus cultured in a variety of climatic conditions was conducted.  It was established that the expression of the virulence gene varies between isolates and culture conditions in vitro.

Footrot lesion swabs were pooled to evaluate the feasibility of pooling samples to detect and identify the serogroups of D. nodosus isolates present in a flock. Three multiplex PCR assays were used and whilst the test sensitivity and specificity varied between DNA and lysate samples from the swabs, pooling five DNA samples may be a method to improve the cost effectiveness of testing.

The efficacy of a serogroup-specific bi-valent fimbrial vaccine against benign and intermediate footrot was trialled at four farms in NSW. The study demonstrated the use of the serogroup-specific vaccine can be effective at controlling some intermediate strains of D. nodosus. The number and severity of foot lesions reduced following vaccination and the number of lame animals observed within the trial mobs was also reduced.

Farmers’ attitudes towards footrot and other hoof diseases and risk factors associated with the presence of the diseases was explored via a survey of sheep farmers. Farmers largely agreed benign and intermediate footrot causes production losses and impacts the welfare of animals and saw merits in effective treatment and control methods for the less severe forms of footrot.

Importance of the research

The research conducted improves our understanding and knowledge about various aspects of the less severe forms of footrot in NSW. The impact of benign and intermediate footrot is becoming more apparent and with traditional methods used to eliminate often unsuccessful against less virulent strains of D. nodosus. Research conducted in this project is expected to improve the understanding in diagnosis, control and elimination of footrot from flocks, benefiting farmers and the sheep industry of NSW.

The research was co-funded by the Rural Assistance Authority and the McGarvie Smith Institute. The funding provided by the McGarvie Smith Institute provided support for a scholarship which allowed time to be committed to the research project which is of importance to the sheep industry of NSW.

Download the final report for this research