A method for tracking the spread of a new Campylobacter species

“At first, we were contacted by veterinarians” explains Martine Denis, Head of the National Reference Laboratory (NRL) for Campylobacter at ANSES. “They had observed cases on poultry farms evoking symptoms caused by Campylobacter hepaticus. Conventional culturing methods for Campylobacter were not working with this species, making it difficult for testing laboratories to identify it, so they too turned to the NRL for Campylobacter”. Indeed, Campylobacter hepaticus does not develop in the culture media used for other species of the genus Campylobacter.

To find a solution to this problem, the ANSES Ploufragan-Plouzané-Niort Laboratory, which holds the mandate of NRL for Campylobacter in France, coordinated a European project as part of the Collaborating Veterinary Laboratories (CoVetLab) network and worked on Campylobacter hepaticus with the NRLs of other countries. This project brought together the Campylobacter NRLs of Sweden, Denmark, the Netherlands and the United Kingdom. After 18 months of research, they developed a culture protocol specifically for isolating C. hepaticus and adapted a PCR test to confirm that an isolated strain does indeed belong to this species.

A bacterium initially detected in Australia and New Zealand

Unlike other species of the genus Campylobacter, C. hepaticus affects poultry, particularly laying hens, but not humans. “It is responsible for spotty liver disease, which causes a drop in egg-laying and increased mortality. Its most characteristic symptom is the presence of white spots on the liver, hence its name”, explains the scientist. This new species of Campylobacter was first described in Australia and New Zealand in 2014. “These countries first developed a PCR test to detect it directly from liver and bile, but there was no method for culturing it”. The PCR test can identify the presence of the bacterium, but it cannot determine whether it is still alive or to which strain it belongs. To do this, it needs to be cultured and then isolated and genetically characterised.

Understanding how the bacterium enters farms and infects poultry

The newly developed protocol for isolating C. hepaticus from liver or bile requires four days of broth enrichment followed by four days of agar culture, i.e. a total of eight days instead of the four days needed to isolate other Campylobacter species. This protocol has been provided to field testing laboratories so that they can implement it, which will provide a better understanding of how Campylobacter hepaticus spreads on farms. “By isolating strains and characterising their genetic profile, we will be able to determine the origin of the bacterium. We will also be able to find out whether it survives in the environment, for example in soil, water or feed or on the tools used on farms. This will enable us to recommend measures for farmers to prevent poultry from becoming contaminated”. While the prevalence of cases on French farms is not yet known, it has been established that spotty liver disease is more common in summer, when temperatures are high. It is therefore likely that it will become more common in the future as a result of climate change.