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(BRSV)
Pathogenesis
- More serious than PI-3
- Causes [Respiratory Viral Infections - Pathology#Respiratory syncytial virus|respiratory infection]]
- Replicates in nasal epithelium -> throughout upper respiratory tract -> bronchial tree
- Syncytia form -> shed into bronchioles
- Complications include emphysema and oedema, drop in milk yield in adult cattle
Epidemiology
- Subclinical reinfections are important in spreading disease
- More than 70% of cattle in the UK have antibodies to BRSV
Diagnosis
- Diseased lung tissue from dead animals or centrifuged cells from lung lavage
- Virus is too fragile for cell culture isolation (often inactivated in transport)
- Antigen detection by immunocytochemistry for intracytoplasmic viral inclusions containing labelled viral protein
- Serology: 4-fold rise in ELISA antibody in paired serum samples from several animals
Control
- Improve husbandry as in PI-3
- Vaccines are available but not effective as need to stimulate cytotoxic T-cells
Secondary Concerns
- Reference: Bryson, 1999, Update on calf pneumonia, CPD Veterinary Medicine, 1,3, 90-95
- Causative agent Respiratory syncytial virus (RSV), synonym: bovine RSV (BRSV)
- Outbreaks of RSV associated disease usually occur associated with winter housing
- Gross pathology in severe cases
- Cranioventral atelectasis and consolidation
- Interstitial emphysema
- More prominent in the caudal lung lobes
- Results from bronchoconstriction which results in airway obstruction - this constriction is thought to arise from mast cell degranulation and histamine release
- Histologically
- Acute bronchiolitis, characteristic of the bronchiolar response is the formation of syncytial giant cells (formed by proliferating bronchiolar epithelial cells which may contain intracytoplasmic inclusion bodies), alveolar epithelium sometimes affected
- Obstruction of bronchioles by exudate - these may later become obliterated by the fibrous tissue of organisation
- May contribute to Enzootic pneumonia of calves