Enzootic Pneumonia - Calves

Description

A pneumonic disease which is principally of viral origin although mycoplasmas have also been implemented, which are mildly pathogenic unless secondary bacterial infection occurs. In calves a number of infectious agents are involved in the disease. These include Bovine respiratory syncytial virus (BRSV) - can be primary, causes suppression of pulmonary immune response

• • • Parainfluenza- 3 (PI3) - can be primary, causes suppression of pulmonary immune response
    • Bovine viral diarrhoea virus (BVDV) - suppression of pulmonary immune response
    • Adenoviruses
    • Calf coronavirus
    • Bovine herpes viruses
  • Bacteria
    • Manheimia (Pasteurella) haemolytica serotype A1
    • Pasteurella multocida
    • Arcanobacter pyogenes
    • Haemophilus somnus

Acute suppurative pneumonia (Image sourced from Bristol Biomed Image Archive with permission)

Calf pneumonia - chronic, with abscesses, fibrosis (Image sourced from Bristol Biomed Image Archive with permission)

• Range of infectious agents together with managemental and environmental stress cause damage to the respiratory tract
• Causes unthriftiness in animals < 6 months old
• Usually the primary pathogen is a virus, secondary pathogens are bacteria and mycoplasmas
• Pathogens:
  • Mycoplasmas
    • Mycoplasmal bronchitis and pneumonia of calves is an important component of the syndrome of enzootic pneumonia
    • On its own causes Mycoplasmal ("Cuffing") pneumonia responsible for bronchitis and bronchiolitis and bronchointerstitial pneumonia
    • It is thought to pick up host antigens in order to prevent recognition by the body defences as foreign
    • In uncomplicated mycoplasma infection, the lesions are generally mild and consist of patchy red/purple areas of atelectasis in the cranio-ventral lung lobes
    • More confluent areas can develop with an underlying bronchointestitial pneumonia and resulting atelectasis
    • M. bovis
      • Most pathogenic
      • Widespread lymphofollicular accumulations which contain germinal centres develop more slowly
      • These lesions can result in narrowing of the bronchiolar lumina - this is the classical lesion of ‘cuffing pneumonia’
    • M. dispar
    • Ureaplasma sp.
  • Viruses
• All transmitted by aerosol and direct contact
• Gross pathology:
  • Consolidation of the cranioventral areas which increases in volume with duration
  • On cut surface, exudate in the main airway of affected lobules with thickening of the surrounding connective tissue
• Micro pathology:
  • Substantial lymphoid tissue around the airways
  • Even to proper follicle formation, some of which may be large enough to compress the lumen
  • Mixed cell exudate in the airway lumen
  • Partial alveolar collapse distal to the compression
  • Alveolar exudate contains a mixture of inflammatory cells
  • Slight thickening of the alveolar walls with lymphocytes