BRSV infection is the most common viral pathogen implicated in outbreaks of bovine respiratory disease complex seen in young beef and dairy cattle. BRSV is closely related to human respiratory syncytial virus (HRSV); however, there is no evidence that cross-species transmission between cattle and human beings occurs. BRSV modulates the immune response to avoid stimulation of a vibrant CD8+ T cytotoxic cell response and instead promotes a Th2 response.
Affected calves and young cattle usually present with fever, depression, respiratory distress, conjunctivitis and nasal discharge. Subcutaneous emphysema may occur. Secondary bacterial pneumonia is a frequent occurrence. A biphasic disease pattern has been described but is not consistent.
On calves which have died, postmortem often reveals a diffuse interstitial pneumonia with subpleural and interstitial emphysema.
Diagnosis of BRSV can be difficult due to difficulty in isolating the virus. ELISA and PCR testing are rapid antigen detection assays for accurate detection of humoral antibodies or isolation of viral particles respectively. Fluorescent antibody and immunoperoxidase staining have also provided useful support for making a diagnosis.
Passively derived immunity does not appear to prevent BRSV infections but will reduce the severity of disease.
Broad-spectrum antimicrobial therapy will help minimise clinical signs. Intravenous fluid therapy may be indicated in sick valuable calves. The majority of cases recover in several days without treatment.
Inactivated and modified live vaccines are available and may serve to reduce losses associated with BRSV. The development of safe and effective RSV vaccines has been hampered by the need to induce protective immunity within the first month of life, at a time when maternal antibodies can pose a major obstacle to successful vaccination; and the observation that vaccination can exacerbate RSV disease.
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