Abstract
New vaccine formulations that include novel strains of Mycoplasma hyopneumoniae and innovative adjuvants designed to induce cellular immunity could improve vaccine efficacy against this pathogen. The aim of this experimental study was to assess the efficacy of three experimental bacterin formulations based on M. hyopneumoniae field strain F7.2C which were able to induce cellular immunity. The formulations included a cationic liposome formulation with the Mincle receptor ligand trehalose 6,6-dibehenate (Lipo_DDA:TDB), a squalene-in-water emulsion with Toll-like receptor (TLR) ligands targeting TLR1/2, TLR7/8 and TLR9 (SWE_TLR), and a poly(lactic-co-glycolic acid) micro-particle formulation with the same TLR ligands (PLGA_TLR). Four groups of 12 M. hyopneumoniae-free piglets were primo- (day (D) 0; 39 days of age) and booster vaccinated (D14) intramuscularly with either one of the three experimental bacterin formulations or PBS. The pigs were endotracheally inoculated with a highly and low virulent M. hyopneumoniae strain on D28 and D29, respectively, and euthanized on D56. The main efficacy parameters were: respiratory disease score (RDS; daily), macroscopic lung lesion score (D56) and log copies M. hyopneumoniae DNA determined with qPCR on bronchoalveolar lavage (BAL) fluid (D42, D56). All formulations were able to reduce clinical symptoms, lung lesions and the M. hyopneumoniae DNA load in the lung, with formulation SWE_TLR being the most effective (RDSD28–D56 −61.90%, macroscopic lung lesions −88.38%, M. hyopneumoniae DNA load in BAL fluid (D42) −67.28%). Further experiments raised under field conditions are needed to confirm these results and to assess the effect of the vaccines on performance parameters.
Highlights
Mycoplasma hyopneumoniae (M. hyopneumoniae) is the primary pathogen of enzootic pneumonia (EP) in pigs
Clinical and performance parameters General health, severity of coughing and average daily gain (ADG) of each piglet were closely monitored during the Quantitative PCR for M. hyopneumoniae DNA and routine bacteriological culture on bronchoalveolar lavage fluid The number of animals positive for M. hyopneumoniae DNA in BAL fluid and mean log copies M
The present study assessed the protective efficacy of three innovative M. hyopneumoniae bacterin formulations in a porcine experimental challenge model
Summary
Mycoplasma hyopneumoniae (M. hyopneumoniae) is the primary pathogen of enzootic pneumonia (EP) in pigs. This chronic respiratory disease is responsible for major economic losses in pig producing countries all over the world due to reduced performance and increased medication use [1, 2]. Cell-mediated immune responses, T helper (Th) 1, Th17 and CD8+ T cell responses, are considered to play a major role in protective immunity against M. hyopneumoniae infections [13,14,15,16]. T helper 1 cells are considered to contribute to protection against Mycoplasma infections by activating macrophage killing [14], while Th17 cells protect the lung mucosa by elevating secretory IgA levels [17] and recruiting neutrophils for pathogen clearance [18]. T helper 1 cells are considered to contribute to protection against Mycoplasma infections by activating macrophage killing [14], while Th17 cells protect the lung mucosa by elevating secretory IgA levels [17] and recruiting neutrophils for pathogen clearance [18]. CD8+ T cells, on the other hand, might dampen the excessive pro-inflammatory Th responses that induce lung lesions and clinical disease [19]
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