Abstract
BackgroundHaemophilus parasuis is a commensal pathogen in the swine upper respiratory tract and causes Glässer’s disease. Surveillance, screening for infection, and vaccination response of H. parasuis is hindered by the lack of a rapid antibody detection method.ResultsIn the present study, a monomeric autotransporter was identified as a novel antigen for developing an indirect ELISA. The autotransporter passenger domain (Apd) was expressed, purified, and demonstrated to be specific in ELISA and western blotting. Mouse antiserum of recombinant Apd (rApd) recognized native Apd in the 15 serotype reference strains and five non-typeable isolate stains, but showed no reaction with seven other bacterial pathogens. The rApd ELISA was optimized and validated using 67 serum samples with known background, including 27 positive sera from experimentally infected and vaccinated pigs along with 40 negative sera that had been screened with H. parasuis whole cell ELISA from clinically healthy herds. The rApd ELISA provided positive and negative percent agreements of 96.4 and 94.9%, respectively, and an AUC value of 0.961, indicating that the assay produced accurate results.ConclusionApd was a universal antigen component among 15 serotype and non-typeable strains of H. parasuis and was also specific to this pathogen. The rApd ELISA could detect antibodies elicited by H. parasuis infection and vaccination, thereby exhibiting the potential to be applied for Glässer’s disease diagnosis, H. parasuis vaccination evaluation, and large-scale serological surveillance.
Highlights
Haemophilus parasuis is a commensal pathogen in the swine upper respiratory tract and causes Glässer’s disease
RApd was selected as the diagnostic antigen for antibody detection enzyme-linked immunosorbent assays (ELISA) of H. parasuis
The antibodies induced by H. parasuis commercial killed vaccine and infection were both detectable via the recombinant Apd (rApd) ELISA (Fig. 3), which is consistent with the findings that autotransporters of H. parasuis were able to be expressed in in vitro culture as well as in in vivo infection of pigs [15]
Summary
Haemophilus parasuis is a commensal pathogen in the swine upper respiratory tract and causes Glässer’s disease. Haemophilus parasuis, a member of the family Pasteurellaceae, constitutes an early colonizer of the swine upper respiratory tract [1]. Liu et al BMC Veterinary Research (2019) 15:436 pathogens [6]. In such cases, it is necessary to diagnose Glässer’s disease according to serological assays. Serological assays are further required for epidemiological surveillance of Glässer’s disease as well as for evaluating the antibodies elicited by the several commercial inactive vaccines of H. parasuis. IHA and ELISA based on oligopeptide permease A (OppA) could discriminate the sera of the convalescent pigs from those of specific pathogen-free and clinically normal healthy pigs [4, 5, 10]. OppA protein is present in other swine bacterial pathogens, such as Actinobacillus pleuropneumoniae, Escherichia coli, Salmonella enteric and Yersinia pestis [5, 11 12], which might afford cross-reactions because of similar antigen epitopes
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