Date Full Report Received08/28/2020
Date Abstract Report Received08/28/2020
Bacterial respiratory pathogens of swine cost swine producers millions of dollars annually due to increased morbidity and mortality, elevated treatment costs, and production losses including reduced feed efficiency and reduced growth rates. Controlling bacterial respiratory disease in pigs has been done using antibiotic treatment and vaccine strategies. For many bacterial pathogens, vaccines are generated from inactivated bacteria (bacterin vaccine) and vaccine effectiveness is dependent on similarity between the vaccine strain and the strain circulating within the herd. For respiratory bacteria such as Glaesserella parasuis (formerly Haemophilus parasuis) and Streptococcus suis, bacterin vaccines often generate serovar or strain specific immunity that only provide protection against a single strain or strains producing the same capsule type. More recently, vaccine development has focused on identification of individual proteins that are widely distributed and have little variability within the bacterial species. Identified proteins can be employed as a subunit vaccine, which would be expected to provide more broadly cross protective immunity and avoid the strain or serovar specific immunity often seen with bacterin vaccines. The goals of this project were to 1) identify novel vaccine targets using immunoproteomic approaches (methods that use the immune response to detect proteins of interest) and 2) evaluate identified proteins as a subunit vaccine in pigs. This project’s overarching purpose was to develop and determine the efficacy of novel mechanisms for the identification of subunit vaccine candidates.
Previously, we tested two serovar 5 G. parasuis isolates (HS069 and Nagasaki) as bacterin vaccines. Both vaccines were tested for the ability to prevent systemic disease with the homologous (vaccine) strain as well as a heterologous serovar 1 strain (12939). We found the HS069 bacterin prevented systemic disease after challenge with HS069 and 12939, while the Nagasaki bacterin prevented systemic disease only following Nagasaki challenge. We compared the antibody response from both vaccine groups and found HS069 and Nagasaki stimulated similar antibody levels; however, when visualizing the proteins targeted by bacterin generated antibodies, we saw differences between the two vaccines. These differences were further examined to detect vaccine candidates using immunoproteomic techniques that compared the protective (HS069) and non-protective (Nagasaki) immune response (goal 1). We used two different immunoproteomic approaches and identified a total of 24 unique proteins (12 proteins from each approach). Some of these proteins were identified as known virulence factors or previously identified vaccine candidates utilized in mice. Of the 24 unique proteins, we selected seven for follow up testing. Initial screening of three candidate proteins (goal 2) was completed with a small animal study. Pigs were vaccinated twice with the subunit vaccine (4 pigs) or a mock vaccine (3 pigs) and challenged with HS069 (homologous strain). Improved survival was seen in subunit vaccinated pigs (3/4) as compared with mock vaccinated pigs (0/3). A larger follow up study to test protection against 12939 (heterologous) is currently underway. Additionally, we are continuing to investigate the other candidate proteins identified in this study. The preliminary work here indicates immunoproteomic techniques using antibody with known disease prevention ability can successfully identify proteins of interest for subunit vaccination. These techniques could be further applied to bacterial pathogens of swine beyond G. parasuis.