Impact of diversity of Mycoplasma hyopneumoniae strains on lung lesions in slaughter pigs

Abstract

The importance of diversity of Mycoplasma hyopneumoniae (M. hyopneumoniae) strains is not yet fully known. This study investigated the genetic diversity of M. hyopneumoniae strains in ten pig herds, and assessed associations between the presence of different strains of M. hyopneumoniae and lung lesions at slaughter. Within each herd, three batches of slaughter pigs were investigated. At slaughter, from each batch, 20 post mortem bronchoalveolar lavage fluid samples were collected for multiple locus variable-number tandem repeat analysis (MLVA), and lung lesions (Mycoplasma-like lesions, fissures) were examined. Multivariable analyses including potential risk factors for respiratory disease were performed to assess associations between the number of different strains per batch (three categories: one strain, two–six strains, ≥seven strains), and the lung lesions as outcome variables. In total, 135 different M. hyopneumoniae strains were found. The mean (min.–max.) number of different strains per batch were 7 (1–13). Batches with two–six strains or more than six strains had more severe Mycoplasma-like lesions (P = 0.064 and P = 0.012, respectively), a higher prevalence of pneumonia [odds ratio (OR): 1.30, P = 0.33 and OR: 2.08, P = 0.012, respectively], and fissures (OR = 1.35, P = 0.094 and OR = 1.70, P = 0.007, respectively) compared to batches with only one strain. In conclusion, many different M. hyopneumoniae strains were found, and batches of slaughter pigs with different M. hyopneumoniae strains had a higher prevalence and severity of Mycoplasma-like lung lesions at slaughter, implying that reducing the number of different strains may lead to less lung lesions at slaughter and better respiratory health of the pigs.

Update onMycoplasma hyopneumoniaeinfections in pigs: Knowledge gaps for improved disease control

“…Information on the impact of strain variability may exert on lung lesions severity and clinical signs onset and duration is still not well defined. Whereas it has been reported that co‐infection with more than one strain resulted in more severe lesions (Michiels et al., ; Villarreal et al., ), such potentiation was not observed in others (Charlebois et al., ). To date, the lack of a known virulence marker together with the coexistence of different strains at individual and farm levels (Nathues, Grosse Beilage, Kreienbrock, Rosengarten, & Spergser, ; Pantoja, Pettit, Dos Santos, Tubbs, & Pieters, ; Vranckx, Maes, Del Pozo Sacristán, Pasmans, & Haesebrouck, ; Vranckx et al., ), prevent knowing the impact of a particular strain on the severity of clinical signs and lung lesions.…”

“…The use of M. hyopneumoniae molecular characterization has aided outbreak and area spread investigations, by tracking specific strains. In addition, it has enabled research directed at understanding pathogen variability and its relationship with disease presentation (Michiels et al., ). However, current tools for M. hyopneumoniae characterization are based on the sole evaluation of similarities in specific loci and do not indicate strain virulence and/or antigenicity.…”

Mycoplasma hyopneumoniaevariability:Current trends and proposed terminology for genomic classification

“…Several M. hyopneumoniae strains can be detected in a herd and even in one individual pig from bronchoalveolar lavage fluid or lung tissue (Michiels et al, ; Nathues, Grosse Beilage, Kreienbrock, Rosengarten, & Spergser, ; Dos Santos et al, ; Vranckx et al, ). Although some studies point in the direction that co‐infection with more than one strain in a pig or batch of pigs might result in more severe lung lesions (Michiels et al, ; Villarreal et al, ; Vranckx et al, ), other studies did not detect such a relationship (Charlebois et al, ). Michiels et al () investigated the genetic diversity of M. hyopneumoniae strains in different successive batches of 10 pig herds using Multiple‐Locus Variable number tandem repeat Analysis (MLVA).…”

“…Although some studies point in the direction that co‐infection with more than one strain in a pig or batch of pigs might result in more severe lung lesions (Michiels et al, ; Villarreal et al, ; Vranckx et al, ), other studies did not detect such a relationship (Charlebois et al, ). Michiels et al () investigated the genetic diversity of M. hyopneumoniae strains in different successive batches of 10 pig herds using Multiple‐Locus Variable number tandem repeat Analysis (MLVA). Multivariable analyses accounting for the potential effect of risk factors for respiratory disease were performed to assess associations between the number of different Variable Number Tandem Repeats (VNTR) variants per batch and lung lesions as outcome variables.…”

“…In comparison, a similar circulation of VNTR types for M. pneumoniae has been shown across different countries (Dégrange et al, ). Furthermore, in swine dense geographical areas, multiple M. hyopneumoniae VNTR types have been identified in endemically infected herds and even in individual pigs (Michiels et al, ; Nathues et al, ; Vranckx et al, ). Greater homogeneity and/or identical M. hyopneumoniae VNTR types in herds that are of close geographical proximity or herds that belong to the same production flow, have also been shown (Charlebois et al, ; Mayor, Zeeh, Frey, & Kuhnert, ; Pantoja, Pettit, Santos, Tubbs, & Pieters, ; Rebaque et al, ; Takeuti et al, ).…”