Development of an enzyme-linked immunosorbent assay for detecting Campylobacter hepaticus specific antibodies in chicken sera - a key tool in Spotty Liver Disease screening and vaccine development

Campylobacter bilis, the second novel Campylobacter species isolated from chickens with Spotty Liver Disease, can cause the disease

Spotty Liver Disease (SLD) is a significant disease of commercial layer hens. It can cause up to 10 % flock mortalities and reduce egg production by 25 %. Campylobacter hepaticus has been identified as the main cause of the disease, although it also appears that predisposing factors, such as some form of stress, may increase the likelihood of clinical disease occurring. Recently, a newly identified species, Campylobacter bilis, was isolated from bile samples of clinical SLD affected chickens. To investigate the pathogenic potential of C. bilis two independent isolates were used in infection trials of layer hens. Within 6 days of oral challenge birds developed typical SLD liver lesions, demonstrating that both strains induced SLD. C. bilis could be recovered from all the challenged birds that developed SLD. Thus, each of the steps in Koch's postulates have been fulfilled, confirming that C. bilis is an additional cause of SLD. A PCR method was developed which can specifically detect C. bilis from samples with complex microbiota. The identification of this newly discovered Campylobacter species as a second cause of SLD and the provision of a rapid method to detect the SLD causing bacterium will help with SLD vaccine development and epidemiology, thus assisting in the control of this important disease of poultry.

The use of filamentous hemagglutinin adhesin to detect immune responses to Campylobacter hepaticus infections in layer hens

Campylobacter hepaticus is the aetiological agent of Spotty Liver Disease (SLD). SLD can cause significant production loss and mortalities among layer hens at and around peak of lay. We previously developed an enzyme linked immunosorbent assay (ELISA), SLD-ELISA1, to detect C. hepaticus specific antibodies from bird sera using C. hepaticus total proteins and sera pre-absorbed with Campylobacter jejuni proteins. The high specificity achieved with SLD-ELISA1 indicated the presence of C. hepaticus specific antibodies in sera of infected birds. However, some of the reagents used in SLD-ELISA1 are time consuming to prepare and difficult to quality control. This understanding led to the search for C. hepaticus specific immunogenic proteins that could be used in recombinant forms as antibody capture antigens in immunoassay design. In this study, an immunoproteomic approach that combined bioinformatics analysis, western blotting, and LC MS/MS protein profiling was used, and a fragment of filamentous hemagglutinin adhesin (FHA), FHA_1,628-1,899 with C. hepaticus specific antigenicity was identified. Recombinant FHA_1,628-1,899 was used as antigen coating on ELISA plates to capture FHA_1,628-1,899 specific antibodies in sera of infected birds. SLD-ELISA2, based on the purified recombinant FHA fragment, is more user-friendly and standardizable than SLD-ELISA1 for screening antibody responses to C. hepaticus exposure in hens. This study is the first report of the use of FHA from a Campylobacter species in immunoassays, and it also opens future research directions to investigate the role of FHA in C. hepaticus pathogenesis and its effectiveness as a vaccine candidate.

Prevalence of Campylobacter hepaticus specific antibodies among commercial free-range layers in Australia

Spotty liver disease (SLD) caused by Campylobacter hepaticus affects the health and productivity of layer hens and is a disease of concern in poultry. In this study, blood and cloacal swab samples were collected from 709 birds across 11 free-range layer farms from different regions of Australia. The prevalence of C. hepaticus specific antibodies and DNA was assessed using a C. hepaticus specific ELISA and PCR and its correlation with mortalities and changes in egg production was analyzed to better understand the seroprevalence of C. hepaticus in Australian free-range layer farms. C. hepaticus specific antibodies were detected from birds in four of the five farms that had no history of SLD with seroprevalence as high as 41% in one of the farms. Seroprevalence of anti-C. hepaticus antibodies among flocks that had an active or previous SLD outbreak varied between 2 and 64%. C. hepaticus DNA was detected from birds in three farms with no known SLD history and five farms with confirmed SLD outbreaks. A good correlation was observed between the ELISA and PCR results with a Pearson correlation coefficient value of 0.85 (p-value = 0.001). No correlation was observed between the flock size or flock age and ELISA or PCR outcomes, and no significant difference between the seroprevalence of anti-C. hepaticus antibodies among flocks with or without a known history of SLD was established (p = 0.143). This study demonstrates the usefulness of C. hepaticus specific ELISA and PCR in identifying the occurrence of mild or sub-clinical SLD and provides a broader and more complete understanding of SLD epidemiology that will inform future research aimed at the development of methods to control SLD, such as appropriate biosecurity measures, vaccines, and feed additives.