Short communicationHistochemical and morphometric characterization of broncho-pneumonia in calves caused by infection with Mycoplasma bovis
Introduction
Mycoplasma bovis is a pathogen that is frequently isolated from the nasal cavity of cattle and causes pneumonia, mastitis, polyarthritis, otitis media and keratoconjunctivitis (Alberti et al., 2006, Arcangioli et al., 2008, Hale et al., 1962, Krysak, 2006, Walz et al., 1997). M. bovis establishes a chronic infection in calves, resulting in an unresponsive pneumonia and polyarthritis, and causes significant economic loss in the beef industry (Shahriar et al., 2002). Natural infection of M. bovis causes cranioventral consolidation of the lungs, with caseous or coagulative multifocal lesions, characterized by caseonecrotic bronchopneumonia with peribronchiolar mononuclear cell cuffing (Gagea et al., 2006, Khodakaram-Tafti and López, 2004), while experimental infections generally produce milder lesions (Caswell and Archambault, 2008, Rodriguez et al., 1996, Thomas et al., 1986). Many naturally occurring cases of M. bovis pneumonia are a result of synergistic infections with bovine viral diarrhoea virus and the bacterial pathogens Mannheimia haemolytica, Pasturella multocida and Histophilus somnus (Haines et al., 2001, Radaelli et al., 2008) and this is likely to explain the considerable variation seen in lung lesions. Studies of both natural and experimental infections have used scoring systems focusing on the grossly apparent lesions, but not examined the pathology of the rest of the lung. We examined the changes in the lung tissue in experimentally infected calves at sites distant from areas of consolidation with the aim of assessing the effect of infection throughout the lung. Examination of the pathological changes during the early stages of experimental infection should provide better insights into the pathogenesis of respiratory mycoplasmosis in cattle. We also aimed to develop a method to quantify the differences in the bronchial epithelium in uninfected and M. bovis infected calves.
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Materials and methods
Twelve three-month-old Jersey-cross male calves, which were tested and found negative for BVDV and M. bovis in nasal and conjunctival swabs by qPCR (Sachse et al., 2009), were separated into two groups. Group 1 consisted of four calves exposed only to mycoplasma culture medium, while group 2 consisted of eight calves exposed to M. bovis strain 3683 (isolated from a joint lesion in a calf in Queensland, Australia). The calves were exposed to aerosol of medium or of an overnight culture, with
Goblet cell ratio
The tip/crypt ratios of goblet cells in the uninfected and infected groups are shown in Table 1. The mean tip/crypt ratio differed significantly between the two groups (P = 0.0001), with a mean tip/crypt ratio in the uninfected group of 0.63 ± 0.07 and in the infected group of 1.01 ± 0.18. The uninfected animals had more goblet cells in the crypts than in the tips of the epithelial folds (Fig. 1). Thus, infection with M. bovis appeared to have induced extension of the goblet cells into the tips of
Discussion
The results of this study have shown that infection with M. bovis induces goblet cell hyperplasia in the bronchial epithelium and an increase in the epithelial height. We also noted goblet cell metaplasia in the smaller bronchioles and reduced epithelial cell diameter. These changes are consistent with the reports of goblet cell hyperplasia and metaplasia, and increased epithelial height, in other mycoplasmal pneumonias (Allan et al., 1977, Jones et al., 1975).
Goblet cells are the first line of
Conflict of interest
The authors have no conflict of interest.
Ethics
The animal experiment was conducted with the approval of The University of Melbourne Animal Ethics Committee, project number 1111970.
Acknowledgements
N.K. Wawegama was supported by the Melbourne International Fee Remission and Melbourne International Research Scholarships. The authors like to thank Ms. F. Doherty for her assistance in preparing and staining the histological sections and Ms. C. Colson for care of the calves during the experiment.
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