Submitted to: American Society for Microbiology General Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/5/2015
Publication Date: N/A
Technical Abstract: Haemophilus parasuis is a Gram-negative bacterium belonging to the Pasteurellaceae family. This bacterium can exist as a commensal in the upper respiratory tract in swine, but can also cause pneumonia and can systemically invade causing Glässer’s disease, which is characterized by polyserositis, meningitis and arthritis. Reports of heterologous protection have been variable, but understanding heterologous protection among strains is critical for the development of cross-protective vaccines. Previously we demonstrated that pigs colonized with a serovar 3 strain of H. parasuis (SW114) were protected from challenge with a heterologous virulent serovar 1strain (12939) demonstrating heterologous protection is possible. However, strain SW114, originally thought to be avirulent, was found to cause disease in immunologically naïve caesarian-derived, colostrum-deprived (CDCD) pigs, suggesting it may not be an ideal strain to use as an attenuated vaccine. To further explore heterologous protection we examined whether pigs colonized with an avirulent serovar 7 strain (174) could protect against a highly virulent serovar 5 strain (Nagasaki). Seven CDCD pigs were inoculated intranasally with 108 CFU of H. parasuis strain 174 and then challenged intranasally 3 weeks later with a lethal dose of strain Nagasaki. Six pigs were also vaccinated parenterally with Nagasaki bacterin given twice 3 weeks apart and then similarly challenged with strain Nagasaki. In addition, 2 naïve animals were challenged. Initial colonization with strain 174 did not result in clinical disease, highlighting the avirulent status of this strain. After challenge with strain Nagasaki, all of the pigs vaccinated with the bacterin and 4 of the pigs colonized with strain 174 showed no clinical signs of disease and H. parasuis was only isolated from the nasal cavity of these pigs. Three of the pigs colonized with strain 174 and both control pigs developed clinical signs of Glässer’s disease, were euthanized, and H. parasuis strain Nagasaki was isolated from systemic sites. Thus we have shown homologous protection and partial to total heterologous protection depending on the strains of H. parasuis examined and we are currently trying to elucidate potential correlates of protection.