Evaluation of serovar-independent ELISA antigens of Actinobacillus pleuropneumoniae in pigs, following experimental challenge with A. pleuropneumoniae, Mycoplasma hyopneumoniae and Pasteurella multocida.
OBJECTIVE
To compare the sensitivity and specificity of six serological enzyme-linked immunosorbent assays (ELISAs) based on serovar-independent antigens of Actinobacillus pleuropneumoniae (App) and investigate cross-reactivity in disease-free pigs challenged with Mycoplasma hyopneumoniae and Pasteurella multocida.


METHODS
Five experimental pig trials using direct challenge with App serovars 1, 7 or 15 or direct challenge with M. hyopneumoniae and/or various dose rates of P. multocida.


METHODS
A 39-kDa outer membrane protein antigen and five recombinant antigens from the apxIVA gene of App were evaluated. The latter were derived from the ApxIVA N-terminus (ApxIVA-N, ApxIVA-NP, ApxIVA-NPS) or C-terminus (ApxIVA-C, ApxIVA-CP). Pigs were sampled after challenge and clinical and necropsy findings evaluated.


RESULTS
The 39-kDa ELISA had high sensitivity but lacked specificity, with significantly increased cross-reactivity following P. multocida challenge. ELISAs based on ApxIVA N-terminus antigens were significantly more sensitive than C-terminus antigens for the detection of App-induced disease. Although ApxIVA-N and ApxIVA-NP ELISAs had increased reactivity following P. multocida challenge, they retained high specificity for App-induced disease (90-93%). Affinity purified ApxIVA-NP antigen had marginally better specificity than ApxIVA-N, without reduced sensitivity. Mycoplasma hyopneumoniae did not affect serological cross-reactivity. In disease-free pigs, the specificity of the ApxIVA-NPS ELISA may be adversely affected by nasal carriage of apparently low-virulence App strains.


CONCLUSIONS
ApxIVA-N-based ELISAs can be used for evaluating App status in commercial herds, but some appear limited by high carriage rates of low-virulence App. The 39-kDa antigen is only of merit in exclusion of App disease by negative serology.
NSW Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Camden New South Wales, 2570, Australia. graeme.eamens@dpi.nsw.gov.au
G J
GJ
Eamens
J R
JR
Gonsalves
A-M
AM
Whittington
B
B
Turner
D000189:Actinobacillus Infections / Q000097:blood / Q000175:diagnosis / Q000382:microbiology / Q000662:veterinary; D016977:Actinobacillus pleuropneumoniae / Q000276:immunology; D000818:Animals; D000942:Antigens, Bacterial / Q000097:blood / Q000276:immunology*; D003429:Cross Reactions; D004797:Enzyme-Linked Immunosorbent Assay / Q000592:standards / Q000662:veterinary*; D008970:Molecular Weight; D045705:Mycoplasma hyopneumoniae / Q000276:immunology; D010326:Pasteurella Infections / Q000097:blood / Q000175:diagnosis / Q000382:microbiology / Q000662:veterinary; D016979:Pasteurella multocida / Q000276:immunology; D045729:Pneumonia of Swine, Mycoplasmal / Q000097:blood / Q000175:diagnosis / Q000382:microbiology; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013045:Species Specificity; D013552:Swine; D013553:Swine Diseases / Q000097:blood / Q000175:diagnosis* / Q000382:microbiology
D000942:Antigens, Bacterial