Effect of challenge of pigs previously immunised with inactivated vaccines containing homologous and heterologous Mycoplasma hyopneumoniae strains

<p>Abstract</p> <p>Background</p> <p><it>Mycoplasma hyopneumoniae </it>is the primary cause of enzootic pneumonia in pigs. Although vaccination is an important control tool, the results observed under field conditions are variable. This may be due to antigenic differences between the strains circulating in pig herds and the vaccine strain. This study compared the protective efficacy of four bacterins against challenge infection with a highly virulent field strain of <it>M. hyopneumoniae</it>.</p> <p>Seventy eight, one-week old piglets were randomly assigned to five treatment groups (A, B, C, D, E), 14 piglets each, and a negative control group (F) consisting of 8 piglets. All pigs were injected at 1 (D7) and 4 weeks of age (D28), with 2 ml of either a placebo or a bacterin based on selected <it>M. hyopneumoniae </it>strains, namely A (F7.2C), B (F20.1L), C (B2V1W20 1A-F), D (J strain), E (placebo; positive control), F (placebo; negative control). At D56, all pigs except those of group F were challenged intratracheally with 7 ml culture medium containing 10⁷CCU/ml of <it>M. hyopneumoniae </it>strain F7.2C. All pigs were euthanized and necropsied at D84. The severity of coughing and pneumonia lesions were the main parameters. Immunofluorescence (IF) testing, nested PCR testing of bronchoalveolar lavage (BAL) fluid and serology for <it>M. hyopneumoniae </it>were also performed.</p> <p>Results</p> <p>The different bacterins only slightly improved clinical symptoms (average 0.38 in vaccinated groups vs. 0.45 in group E) and histopathological lung lesions (average 3.20 in vaccinated groups vs. 3.45 in group E), but did not improve macroscopic lung lesions (score 4.30 vs. 4.03 in group E). None of the vaccines was significantly and/or consistently better or worse than the other ones. All bacterins evoked a serological response in the vaccinated animals. All pigs, except those from group F, were positive with nPCR in BAL fluid at D84.</p> <p>Conclusion</p> <p>The bacterins did not induce a clear overall protection against challenge infection, and there were no significant differences in protective efficacy between bacterins containing homologous and heterologous <it>M. hyopneumoniae </it>strains. Further research is necessary to better characterize the antigens involved in protection and to elucidate the protective immunity responses following <it>M. hyopneumoniae </it>vaccination and/or infection.</p

In vivo virulence of Mycoplasma hyopneumoniae isolates does not correlate with in vitro adhesion assessed by a microtitre plate adherence assay.

Aims: Adherence of Mycoplasma hyopneumoniae to the ciliated epithelial cells of the porcine respiratory tract is considered an important first step in the pathogenesis of enzootic pneumonia. It was the aim of this study to verify the usefulness of in vitro adhesion as a virulence marker. Methods and Results: Adherence capacity to immobilized cilia from porcine tracheal epithelial cells of three low, two moderately and two highly virulent M. hyopneumoniae field isolates was determined by a microtitre plate adherence assay. Conclusions: No significant differences between the isolates were demonstrated. Significance and Impact of the Study: The results suggest that mechanisms other than adherence might be responsible for the observed differences in virulence of these field isolates or that the in vitro assay does not adequately reproduce in vivo adherence conditions

Multiple-locus variable-number tandem-repeat analysis is a suitable tool for differentiation of mycoplasma hyopneumoniae strains without cultivation

An assay based on multiple-locus variable-number tandem-repeat analysis allowed differentiating and studying diversity and persistence of Mycoplasma hyopneumoniae strains in pig herds without prior cultivation. The test had a discriminatory index of > 0.99 and was applied reliably to porcine bronchoalveolar lavage fluid and tracheal swabs