Short communication
Histochemical and morphometric characterization of broncho-pneumonia in calves caused by infection with Mycoplasma bovis

https://doi.org/10.1016/j.vetmic.2012.02.011Get rights and content

Abstract

The aim of this study was to identify morphometric histological features of pneumonia caused by Mycoplasma bovis in calves. Eight three-month-old calves were infected with M. bovis and samples of their lung tissue, three weeks after exposure, compared to samples from four uninfected calves. In the uninfected animals the goblet cells were clustered in the crypt area of the epithelial folds, while in the infected calves they had migrated towards the tips of the folds and were distributed evenly throughout the folds. In infected lung tissue there was goblet cell hyperplasia and metaplasia in the bronchioles and an increased epithelial height. Goblet cell mucin in uninfected calves was acidic, but in infected calves most goblet cells contained neutral mucins. These morphometric and histochemical bronco-epithelial changes may be able to be used as markers of the severity of bovine respiratory mycoplasmosis.

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.

Section snippets

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.

References (24)

  • D.M. Haines et al.

    The immunohistochemical detection of Mycoplasma bovis and bovine viral diarrhea virus in tissues of feedlot cattle with chronic, unresponsive respiratory disease and/or arthritis

    Can. Vet. J.

    (2001)
  • H.H. Hale et al.

    Bovine mastitis caused by a Mycoplasma species

    Cornell Vet.

    (1962)
  • Cited by (8)

    • Membrane proteins of Mycoplasma bovis and their role in pathogenesis

      2013, Research in Veterinary Science
      Citation Excerpt :

      Using human surfactant protein-A (hSP-A)-coupled Sepharose affinity chromatography and polyacrylamide gel electrophoresis, Kannan et al. (2005) identified a 65 kDa hSP-A binding protein of M. pneumoniae. Experimental infection of calves with an aerosolised culture of M. bovis has been shown to induce goblet cell hyperplasia and metaplasia in the bronchial epithelium and an increase in the epithelial height, although affects on pulmonary surfactant have yet to be investigated (Wawegama et al., 2012). There remains a great deal of work to do to classify the M. bovis ORFs that have no match in the current databases and to assign functions to these ORFs, as well as to definitively assign function to those ORFs with predicted roles.

    View all citing articles on Scopus
    View full text