Understanding and tackling Spotty Liver Disease in poultry

Understanding and tackling Spotty Liver Disease in poultry

RMIT University researchers identified the bacterial species that causes Spotty Liver Disease in chickens and developed diagnostic tools for the serious issue that is affecting global egg production industries.

The research was initiated by Professor Rob Moore in 2013, and since 2015, together with Associate Professor Thi Thu Hao Van, they have expanded the team and made significant contributions to the field.

Associate Professor Thi Thu Hao Van has secured various funding awards from Australian Eggs and Poultry Hub Australia for this research area and is now leading the research program at RMIT.

Rob Moore profile photo he is smiling while wearing a suit and glasses

RMIT’s Professor Rob Moore is an internationally recognised veterinary microbiologist.

His research portfolio encompasses studies on bacterial pathogens, vaccination, genomics, gut microbiota, and probiotics. Moore’s research investigating host-pathogen interactions, and his collaborative work with industry includes significant contributions towards understanding the pathogenesis of Spotty Liver Disease in chickens.

RMIT’s Associate Professor Thi Thu Hao Van is an internationally recognised molecular microbiologist.

Her team collaborates closely with industry, focusing on identifying bacterial pathogens in poultry, deciphering their biology, developing vaccines and other intervention strategies to combat bacterial diseases, and researching beneficial bacteria to improve gut and overall health. She has made significant breakthroughs, including culturing and identifying the bacterium responsible for Spotty Liver Disease, which had remained unidentified since the disease was first recognised 60 years ago.

Spotty Liver Disease - the challenge

Spotty Liver Disease (SLD) in chickens is one of the most common and serious health issues for the Australian egg production industry. The infectious disease mainly affects free-range laying chickens, with outbreaks causing reduced egg production and increased mortality.

Monitoring of commercial poultry flocks has shown that the disease can cause up to a 15% increase in mortalities and 20% reduction in egg production. It is estimated that around 50 percent of flocks in Australia are currently being infected at some stage during their production cycle, resulting in around 9 million dozen eggs being lost each year. The direct cost of this issue for Australia’s $1.1 billion egg production industry is around $18 million per year.

Moore said that although SLD had been recognised for more than 50 years, its cause had remained a mystery.

The disease remains an ongoing problem and all involved in the egg production industry are desperate to find a solution.

Successfully identifying the cause

In 2015, Moore’s team began a research program that aimed to identify the cause of the disease so that appropriate treatment options could be developed.

The team used a new high throughput DNA sequencing technology to provide clues about the bacterial pathogen that could be causing the disease.

By 2016 they had published research on successfully isolating, characterising, and naming a newly identified species of bacteria that they proposed was causing SLD, Campylobacter hepaticus. The team then published definitive proof that this species was the cause in 2017.

Recently, the group has isolated and identified a second novel species of Campylobacter, Campylobacter bilis, from a few SLD affected flocks in Australia. C. bilis is closely related but distinct from C. hepaticus.

Developing tools to detect birds infected with Spotty Liver Disease

After identifying what was causing the disease, the team developed a sensitive and highly specific molecular test (PCR) for detecting the bacterial pathogen in clinical and environmental samples.

They also developed immunological assays to detect birds that have raised an immune response to infection.

For the first time globally, this allowed farmers and the egg production industry to accurately diagnose Spotty Liver Disease in flocks and to implement strategies to try and reduce its effects.

Moore said close collaborations with industry partners have been key throughout the research program.

Important collaborations included working with Scolexia Pty Ltd, a local veterinary consulting company that services a large proportion of the Australian egg layer industry.

“Scolexia have given us access to vital resources and information including clinical samples from the field, and knowledge about the disease, such as the extent and management of the disease in the poultry industry,” said Moore.

Scanning electron micrographs of a colony of Campylobacter hepaticus. Scanning electron micrographs of a colony of Campylobacter hepaticus.

Research outcomes and impact

Identifying the global spread of the disease

Moore said the tests and assays developed by the team have allowed groups around the world to identify the disease, resulting in a new understanding of its global prevalence.

“Historically, Spotty Liver Disease was regarded as being an issue for farmers and the egg production industry mostly just in Australia and Britain,” he said.

However, now that we can detect the bacteria and diagnose the disease correctly, it is being recognised as an issue around the world.

In the last few years, reports have been published from the USA, New Zealand, Germany, Costa Rica, and Jordan.There are also anecdotal reports of cases being diagnosed in most European countries and many Asian countries that we hear about at conferences and through our network.

Van said that the team has recently developed breakthrough genetic manipulation technologies, credited to PhD student Jamieson McDonald, enabling researchers to manipulate the genomes of the bacteria causing SLD.

This advancement enhances our understanding of the roles of key virulence genes, which will be greatly beneficial for vaccine development.

Understanding how the disease spreads, monitoring flocks, and reducing the risk

These diagnostic tools have also been used to complete epidemiological studies of SLD, allowing greater insights about when birds become infected and how the infection spreads. Insights include identifying that the faecal-oral route as the most likely means of transmission within a flock. Van said that both the PCR and immunological assays are useful for the industry and researchers, and they have been applied in various countries to assess birds’ current and past exposure to C. hepaticus, contributing to the understanding and efforts to combat this important disease. “The greatest impacts of our work so far have been enabling the poultry industry to identify and monitor the pathogenic agent,” said Van.

“However, although the pathogen is most effectively managed using antibiotics, the animal production industries are rapidly moving away from using them, and so alternative methods of treatment are needed.

“The tools we have provided help to analyse the effectiveness of other approaches such as phytobiotics and probiotics, but to date no highly effective alternative treatment has been found.”

Transmission electron micrographs of Campylobacter hepaticus. Transmission electron micrographs of Campylobacter hepaticus.

Next steps – developing a vaccine against Campylobacter species

Van said the team has identified the causes of the disease and developed the necessary tools to enhance understanding of it. Now is the time to search for an effective vaccine for this important poultry disease, particularly with the impending transition away from caged egg production in Australia and numerous other countries. The four-year  Australian Research Council Linkage Project began in 2021 and aims to produce a general anti-Campylobacter vaccine for use in chickens. The London School of Hygiene and Tropical Medicine is also partnering with the team by providing technology for various aspects of the project.

The vaccine being developed is expected to be effective against both Camplyobacter jejuni, the biggest cause of food poisoning in humans and Campylobacter hepaticus.

Van said they are actively seeking additional funding to develop an innovative vaccine for the disease, with the aim of safeguarding the future of our food supply.

Acknowledgements

Significant contributions from former and current PhD students, postdocs, and research assistants — Dr Chithralekha Muralidharan, Dr Canh Phung, Sarah Eastwood, Jamieson McDonald, and Dr Ben Wade, — are gratefully acknowledged.

Funding support

Funding for this program of research has included support from Scolexia Pty Ltd, Australian Eggs, Poultry Hub Australia and from the Australian Government’s Innovation Connections scheme, Bioproperties Pty Ltd and an Australian Research Council Linkage Grant. 

SDGs

Spotty Liver Disease chickens Campylobacter hepaticus egg production industry
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