Serological responses to two serovar-independent ELISA antigens of Actinobacillus pleuropneumoniae in Australian commercial pig herds

• Published in: Australian veterinary journal 2008-12, Vol.86 (12), p.465-472
• Main Authors: Eamens, G.J, Gonsalves, J.R, Whittington, A.M, Turner, B
• Format: Article
• Language: English
• Subjects: Actinobacillus Infections - blood; Actinobacillus Infections - diagnosis; Actinobacillus Infections - veterinary; Actinobacillus pleuropneumoniae; Actinobacillus pleuropneumoniae - classification; Actinobacillus pleuropneumoniae - immunology; Age Factors; Animals; Antigens, Bacterial - immunology; Australia; bacterial antigens; bacterial infections; Cross Reactions; ELISA; enzyme-linked immunosorbent assay; Enzyme-Linked Immunosorbent Assay - methods; Enzyme-Linked Immunosorbent Assay - standards; Enzyme-Linked Immunosorbent Assay - veterinary; Female; health status; herds; Male; maternal immunity; Molecular Weight; pigs; respiratory disease; Risk Assessment; risk factors; Sensitivity and Specificity; serodiagnosis; serotypes; Species Specificity; Swine; swine diseases; Swine Diseases - blood; Swine Diseases - diagnosis
• ISSN: 0005-0423; 1751-0813
• DOI: 10.1111/j.1751-0813.2008.00368.x

Objective  To compare serological responses in pig herds classified as low or high risk for disease caused by Actinobacillus pleuropneumoniae, using two ELISA tests based on serovar‐independent antigens. Procedure  Cross‐sectional sampling was undertaken in 13 commercial herds, the clinical and slaughter histories of which indicated either freedom from (n = 5) or prior confirmed cases of A. pleuropneumoniae (n = 8). In nine herds, approximately 40 pigs each were sampled at 4, 8, 12, 16 and 20 weeks. Three of the remaining four herds were sampled between 6 and 30 weeks of age, and the last was sampled only prior to slaughter, at approximately 24 weeks. Sera were tested in ELISA based on two antigens common among A. pleuropneumoniae serovars: a 39‐kDa outer membrane protein and a recombinant ApxIVA‐N terminus protein. Results  Sampling of 1 and 5 to 6‐month‐old pigs provided the most useful information on herd status. The 39‐kDa ELISA was sensitive in detecting infected herds, but had evidence of cross‐reactivity with high seroreactivity rates in older pigs in some low‐risk herds. The ApxIVA‐N ELISA was less seroreactive in high‐risk herds and had higher specificity in low‐risk herds. Conclusion  ELISA based on the 39‐kDa subunit are of limited use, because of possible cross‐reactivity, but a high negative predictive value may be useful for risk assessment in suspect herds. Maternal antibody to ApxIVA‐N may be of value in detecting high‐risk herds, but 5% of 4‐week‐old pigs in low‐risk herds were also seropositive in this assay.