Date Published: July 25, 2017
Publisher: Public Library of Science
Author(s): Beatriz Garcia-Morante, Joaquim Segalés, Emmanuel Serrano, Marina Sibila, Glenn F. Browning.
One of the main Mycoplasma hyopneumoniae (M. hyopneumoniae) swine experimental model objectives is to reproduce mycoplasmal pneumonia (MP). Unfortunately, experimental validated protocols to maximize the chance to successfully achieve lung lesions induced by M. hyopneumoniae are not available at the moment. Thus, the objective of this work was to identify those factors that might have a major influence on the effective development of MP, measured as macroscopic lung lesions, under experimental conditions. Data from 85 studies describing M. hyopneumoniae inoculation experiments were compiled by means of a systematic review and analyzed thereafter. Several variables were considered in the analyses such as the number of pigs in the experiment, serological status against M. hyopneumoniae, source of the animals, age at inoculation, type of inoculum, strain of M. hyopneumoniae, route, dose and times of inoculation, study duration and co-infection with other swine pathogens. Descriptive statistics were used to depict M. hyopneumoniae experimental model main characteristics whereas a recursive partitioning approach, using regression trees, assessed the importance of the abovementioned experimental variables as MP triggering factors. A strong link between the time period between challenge and necropsies and lung lesion severity was observed. Results indicated that the most important factors to explain the observed lung lesion score variability were: (1) study duration, (2) M. hyopneumoniae strain, (3) age at inoculation, (4) co-infection with other swine pathogens and (5) animal source. All other studied variables were not relevant to explain the variability on M. hyopneumoniae lung lesions. The results provided in the present work may serve as a basis for debate in the search for a universally accepted M. hyopneumoniae challenge model.
Mycoplasma hyopneumoniae (M. hyopneumoniae) has been recognized as the etiological agent of enzootic pneumonia (EP) and a relevant infectious agent of the porcine respiratory disease complex (PRDC). Both are chronic respiratory diseases affecting mainly grow-finishing pigs, causing major economic losses in the pig industry worldwide. Mycoplasmal pneumonia (MP) is grossly characterized by purple to grey areas of pulmonary consolidation, mainly found bilaterally in the apical, cardiac, intermediate and the anterior parts of the diaphragmatic lobes . Such lung lesions can be experimentally induced in pigs inoculated with M. hyopneumoniae .
Numerous attempts to induce MP at experimental level have been reported and, as evidenced by the present results, variation in both the number of animals affected by MP as well as in severity of such lung lesions do occur. The latter is accompanied by wide differences between M. hyopneumoniae experimental models, though highlighting the existing inconstancy between protocols. Works studying how a unique variable may influence MP under experimental settings have been already made [7, 8, 10–13]. Contrarily, observation and analysis of more than one experimental variable at a time has not been assessed. In consequence, a combination of experimental factors that would increase the chance to successfully achieve MP is not available and the uncertainty around this problem is still far of being mitigated. Therefore, the present work investigated which experimental conditions might be accounted for reproduction of MP, determined by the macroscopic lung lesion score, and proposes the initial bases to build are producible and effective M. hyopneumoniae challenge model pursuing this goal.
The present study broadens the current understanding in regards to M. hyopneumoniae experimental swine models and constitutes the first insight into conditions needed to induce lung lesions suggestive of MP under experimental settings. Thus, obtained results might serve as a basis for debate in the search for a M. hyopneumoniae experimental model seeking to induce severe MP. While the M. hyopneumoniae strain used may depend basically on the strain availability, other easily modifiable conditions might be taken into account in experimental models. Therefore, the highest likelihood to achieve severe MP would require lung lesion assessment within a period below 8wpi and include inoculation of SPF (M. hyopneumoniae free) pigs older than3.5 weeks of age and, preferably, in co-infection with another swine respiratory pathogen as a triggering factor.