Spotty Liver Disease (SLD) causes significant egg production losses and mortality in layer birds. The disease was first reported in the 1950s in the USA and then in a series of other countries, including Australia, New Zealand, Canada, Egypt, Germany, Austria, Italy, Hungary, the Netherlands, Bulgaria, Switzerland, UK and Ukraine. Although the disease has been seen for many years the identification of the causative pathogen was elusive until recently identified as Campylobacter hepaticus, a newly recognised Campylobacter species. Recent outbreaks of SLD have been documented in Australia, the UK, and USA and it is now an emerging disease of significant concern for the poultry industry.
The isolation and characterisation of C. hepaticus has allowed us to develop a reproducible disease induction model that we have used to study the virulence of bacterial isolates and has allowed the assessment of various treatment and control options. Molecular tools have been developed to qualitatively and quantitatively detect the organism in clinical samples, enabling the rapid detection of this bacterium in poultry production systems. Whole genome sequencing of C. hepaticus showed that its closest relatives are Campylobacter coli and Campylobacter jejuni, the other common poultry Campylobacter. Core genome sequence alignments showed the nucleotide divergence of C. hepaticus from the former and the latter was ~68% and 63.8% respectively. RNASeq has been carried out to compare the transcriptomes of in vivo (recovered from chicken bile samples) and in vitro (cultured on horse blood agar plates) grown bacteria. The study identified genes and pathways of C. hepaticus, which may contribute to its survival in the competitive, nutrient and energy-limited environment of the chicken. Gene clusters associated with glucose utilisation, stress response, nitrate reductase, hydrogen metabolism, and sialic acid modification may play an important role in the pathogenicity of C. hepaticus. Research directed towards further understanding C. hepaticus virulence mechanisms is progressing to inform efforts to develop intervention strategies.
Dr Hao Van is a Senior Research fellow at School of Science, RMIT University, Australia. Dr Van’s expertise is to apply microbiology and advanced molecular biology skills in identifying the cause of disease in farm animals, understanding the biology of the pathogens causing these diseases and the development of vaccines against these pathogens. She made a breakthrough in poultry research by playing a key role in isolating and identifying the bacteria causing Spotty Liver Disease (SLD) in chickens, which causes high mortality and production losses for the poultry industry. She also works with different groups, nationally and internationally, to study the role of microbiota in animals and humans, and the identification of beneficial bacteria from gut microbiota for use as probiotics.