Bovine Respiratory Syncytial Virus

Introduction

Bovine Respiratory Syncitial Virus (BRSV) is a respiratory condition in cattle that is more serious than PI-3. It replicates in nasal epithelium and then disperses throughout the upper respiratory tract to the bronchial tree. Here, syncytia form and further spread into the bronchioles occurs.

Outbreaks of RSV associated disease usually occur associated with winter housing and also during periods of stress such as mixing of calves and transport. The virus can contribute to calf enzootic pneumonia.

Subclinical reinfections are important in spreading disease and more than 70% of cattle in the UK have antibodies to BRSV.

Classification

BRSV's Baltimore Classification is V, ssRNA negative sense virus, and is a part of the Paramyxovirus family. It is an enveloped virus, utilizing fusion proteins to facilitate cellular fusion and syncytium formation.

Signalment

This virus can occur as part of the calf pneumonia syndrome along with Parainflunza and Herpesvirus (IBR) as well as the bacteria Mannheimia, Mycoplasmas and Pasturella.

It can cause disease in adult cattle too however, it is more severe in young stock.

Clinical Signs

Clinical signs include emphysema and oedema. In adult cattle, you may see a drop in milk yield.

Diagnosis

Often when in combination with other viral agents and bacteria then diagnosis is presumptive due to number of animal affected and the age and circumstances of these (housed etc). A dose of antibiotics is usually given and an effect is often seen quickly.

If the animal has succumbed to the disease a post mortem can be performed to aid diagnosis. Diseased lung tissue from dead animals or centrifuged cells from lung lavage can be used for this. The virus is too fragile for cell culture isolation (often inactivated in transport).

Grossly on post mortem, one will see cranioventral atelectasis and consolidation, interstitial emphysema, which is more prominent in the caudal lung lobes. The results from bronchoconstriction which results in airway obstruction - this constriction is thought to arise from mast cell degranulation and histamine release.

Histologically, one may see 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). The alveolar epithelium is sometimes affected. The bronchioles are often obstructed by exudate and these may later become obliterated by the fibrous tissue of organisation.

Antigen detection by immunocytochemistry for intracytoplasmic viral inclusions containing labelled viral protein can also be performed as well as serology. A 4-fold rise in ELISA antibody in paired serum samples from several animals is indicative of the disease.

Treatment and Control

Treatment with antibiotics is often used to treat secondary infections and lessen clinical signs and help the body focus on eliminating the virus.

It is important to try to improve husbandry as in PI-3 in order to prevent the disease from occurring. Avoiding mixing of different aged calves is very important in the control of the disease, as is good hygiene.

Vaccines are available but not effective as need to stimulate cytotoxic T-cells.

References

Bryson, 1999, Update on calf pneumonia, CPD Veterinary Medicine, 1,3, 90-95

Andrews, A.H, Blowey, R.W, Boyd, H and Eddy, R.G. (2004) Bovine Medicine (Second edition), Blackwell Publishing

Blood, D.C. and Studdert, V. P. (1999) Saunders Comprehensive Veterinary Dictionary (2nd Edition), Elsevier Science

Divers, T.J. and Peek, S.F. (2008) Rebhun's diseases of dairy cattle, Elsevier Health Scieneces

Radostits, O.M, Arundel, J.H, and Gay, C.C. (2000) Veterinary Medicine: a textbook of the diseases of cattle, sheep, pigs, goats, Elsevier Health Sciences

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