Development of an enzyme-linked immunosorbent assay for detectingCampylobacter hepaticusspecific antibodies in chicken sera - a key tool in Spotty Liver Disease screening and vaccine development

Spotty Liver Disease (SLD) is an emerging disease of serious concern in the egg production industry, as it causes significant egg loss and mortality in layer hens. The causative agent is a newly identified Gram-negative bacterium,Campylobacter hepaticus,and knowledge aboutC. hepaticuspathogenesis and the potential for vaccine development is still in its infancy. Current detection methods for SLD, such as PCR and culturing, only detect an active infection and will not give any indication of a past infection from which the bacteria have been cleared. An immunological assay, on the other hand, can provide information on previous infections and therefore is crucial in vaccine development against SLD. In the present study, we have developed the first immunoassay capable of detectingC. hepaticus-specific antibodies present in the sera of infected birds. The assay usesC. hepaticustotal protein extract (TPE) as the antigen coating on enzyme-linked immunosorbent assay (ELISA) plates. The cross reactivity ofC. hepaticusantibodies with closely relatedC. jejuniandC. coliantigens was successfully overcome by pre-absorbing the sera usingC. jejunicell extracts. The assay was validated using sera samples from both naturally- and experimentally-infected birds, birds vaccinated with formalin-killed bacteria, and serum samples from SLD-negative birds (control group). The optimized ELISA assay had 95.5% specificity and 97.6% sensitivity. The immunoassay provides a useful tool for monitoring the exposure of poultry flocks toC. hepaticusinfection and can be used to direct and support vaccine development.