Swine respiratory diseases are of major concern to pork producers because of economic consequences related to reduced productivity, increased mortality, and the higher costs associated with prevention, control, treatments, and diagnoses. Actinobacillus pleuropneumoniae (APP) is the causative agent of porcine pleuropneumonia, a respiratory disease found throughout the world. Pigs are the primary host of APP and infection can occur at any age. APP infections are often acute and rapidly fatal, but chronic and/or subclinical infections occur. In particular, the latter play a role in perpetuating endemic infections in populations.

A plethora of methods have been developed for the detection and/or diagnosis of APP, e.g., bacterial culture, antibody-based assays, and detection of nucleic acid targets using PCR. In particular, antibody detection provides an efficient, cost-effective approach for the surveillance of swine populations and several antibody assays have been developed, including ELISA assays based on polysaccharide antigen (capsular and LPS) and tests based on the detection of anti-toxin antibodies Apx I, ApxII, ApxIII, and ApxIV.

Research has shown that the use of oral fluid specimens in diagnosis provides several advantages compared serum, including easier sample collection and better herd-level sensitivity and specificity (Olsen et al., 2013). Within this context, the focus of this thesis was on the development of an antibody ELISA for the detection of Actinobacillus pleuropneumoniae (APP) ApxIV toxin antibodies in swine oral fluid specimens.

As described in Chapter 3, antibody responses specific for ApxIV in serum and oral fluid were compared in pigs inoculated with APP serovars 1, 5, 7, or 12 under experimental conditions using a commercial ApxIV antibody ELISA. The detection of antibodies in the oral fluid was achieved by adapting the serum ELISA protocol was adapted to the oral fluid matrix, as has been previously described (Kittawornrat et al., 2013). Serum samples were collected weekly and oral fluid samples were collected daily from individual pigs from day post inoculation (DPI) -14 through DPI 56. The LPS ELISA serum response showed that all pigs exposed to serovars 1 and 7 were positive from DPI 14 through DPI 56, with some animals demonstrating a LPS-specific IgG response as early as 7 DPI. In contrast, the LPS antibody response was transient or absent in pigs inoculated with serovars 5 and 12, suggesting that inoculation of pigs did not result in infection. Both IgM and IgG ApxIV serum antibody was detected in animals infected with serovars 1 and 7. Likewise, oral fluid samples from these animals showed a significant (p < 0.05) ApxIV IgG response. Thus, this pilot experiment suggested that ELISAs based on the detection of ApxIV IgG antibody in oral fluid samples could be developed. Future work will be required to establish the ApxIV oral fluid ELISA cutoff and evaluate the application of the assay in the field.