Bovine Respiratory Syncytial Virus (BRSV)
Family - Paramyxoviridae
subfamily - Pneumovirus

BRSV is a non-hemagglutinating, cytopathic, enveloped, single-stranded RNA virus.  BRSV is an  important component in the Bovine Respiratory Diseases Complex and predisposes animals to secondary bacterial infections.4

Clinical Signs:
Clinical signs vary depending on a number of factors such as age, immune status, route of infection and strain of virus.  BRSV most often affects animals 3-12 months of age.  The duration of the clinical signs last approximately 1-2 weeks often with a biphasic course.  
Fever (40-42°C)
Elevated Respiratory Rate Nasal and Lacrimal Discharge Cough
 increased bronchial  sounds    2° bacterial infection tachypnea, dyspnea and later mouth breathing 
Decreased  feed intake decreased milk production inter-mandibular edema and/or subcutaneous emphysema   

Transmission and Pathogenesis:
Transmission of BRSV occurs by direct contact with infected animal or inhalation of large droplets via aerosol.  The incubation period is 3-5 days.  BRSV is characterized by high morbidity and variable mortality (0-20% of cases).  Adult cattle may periodically be subclinically infected and serve as a source of infection.4

Once exposed, the virus replicates in the epithelial cells of the respiratory tract, type II pneumocytes and alveolar macrophages.   The virus decreases opsonization and phagocytosis by the alveolar macrophages and induces cytopathic losses of cilia and/or bronchial epithelial cell.  This decreases the mucocilliary clearance and allows an accumulation of debris and fluids which provides an optimal environment for opportunistic bacteria. 8

Diagnosis can only be made by technical laboratory support. 
Fluorescent antibody and immunoperoxidase-staining techniques may be completed on samples from the respiratory tract.  Tracheal washes and broncho-alveolar lavage provide the best samples.  Samples should be transported in sucrose containing medium to keep the virus viable for testing.  Atypical interstitial pneumonia with subpleural or interstitial emphysema may be described during a necropsy. 8

Treatment and Control:
There is no treatment for BRSV.  Treatment should be provided for 2° complication with antimicrobials for 3-5 days.  Control is the best management.  A number of vaccines, both killed and modified live are available for BRSV.