In a paper published recently in BMC Veterinary Research, Katleen Vranckx and colleagues at Ghent University in Belgium report that Mycoplasma hyopneumoniae is the causative agent of enzootic pneumonia and is responsible for significant economic losses to the pig industry.

To understand better the mode of action of a commercial, adjuvanted, inactivated whole cell vaccine and the influence of diversity on the efficacy of vaccination, they investigated samples from vaccinated and non-vaccinated pigs experimentally infected with either a low (LV) or a highly virulent (HV) M. hyopneumoniae strain.

Non-vaccinated and sham-infected control groups were included. Lung tissue samples collected at four and eight weeks post infection were immunohistochemically tested for the presence of T-lymphocytes, B-lymphocytes and macrophages in the bronchus-associated lymphoid tissue (BALT).

The number of M. hyopneumoniae organisms in bronchoalveolar lavage (BAL) fluid was determined using quantitative PCR at four and eight weeks post infection. Serum antibodies against M. hyopneumoniae were determined at zero, two, four, six and eight weeks post infection.

The immunostaining revealed a lower density of macrophages in the BALT of the vaccinated groups compared to the non-vaccinated groups. The highest number of M. hyopneumoniae organisms in the BAL fluid was measured at four weeks PI for the HV strain and at eight weeks PI for the LV strain.

Vaccination reduced the number of organisms numerically although for the HV strain, the reduction was clinically more relevant than for the LV strain. At the level of the individual pigs, a higher lung lesion score was associated with more M. hyopneumoniae organisms in the lungs and a higher density of the investigated immune cells in the BALT.

The infiltration of macrophages after infection with M. hyopneumoniae is reduced by vaccination, concluded Vranckx and co-authors. They added that M. hyopneumoniae replication in the lungs is also reduced in vaccinated pigs although the HV strain is inhibited more than the LV strain.

Reference

Vranckx K., D. Maes, S.B. Marchioro, I. Villarreal, K. Chiers, F. Pasmans and F. Haesebrouck. 2012. Vaccination reduces macrophage infiltration in bronchus-associated lymphoid tissue in pigs infected with a highly virulent Mycoplasma hyopneumoniae strain. BMC Veterinary Research, 8:24. doi:10.1186/1746-6148-8-24

Further Reading

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You can view the full report (as a provisional PDF) by clicking here.

Further Reading

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Find out more information on enzootic pneumonia by clicking here.

April 2012