Enzootic Pneumonia - Calves

Description

A pneumonic disease which is caused by a range of infectious agents in combination with management and environmental stress causing damage to the respiratory tract. It is principally of viral origin includingBovine respiratory syncytial virus (BRSV), Parainfluenza- 3 (PI3), Bovine viral diarrhoea virus (BVDV), Adenoviruses, Calf coronavirus, Bovine herpes viruses. Mycoplasmas hve also been implemented and secondary bacterial infection commonly occurs including Manheimia (Pasteurella) haemolytica serotype A1,Pasteurella multocida, Arcanobacter pyogenes and 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)

Signalment

Mainly a problem in calves less than 6 months old and particularly affects 2-10 week old animals. It occurs more commonly in dairy calves than beef calves.

History and Clinical signs

• 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