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Introduction
This virus is of the family paramyxoviridae and its virulence varies with isolates. Alone, this virus does not usually produce severe disease in cattle, but with other agents such Bovine Respiratory Syncitial Virus, Infectious Bovine Rhinotracheitis and bacteria such as Mannheima and Mycoplasmas, makes up the enzootic pneumonia complex which mostly affects calves.
Occurence of the disease is usually thought to be due to stress such as mixing of animals of different age groups, transport and winter housing. Poor hygiene also contributes to this.
The virus causes cessation of ciliary clearance and epithelial necrosis, which predisposes to secondary bacterial infections and can leading to clinical signs. This occurs due to replication in airway epithelial cells causing an initial bronchitis, which may lead to bronchiolitis and then extension into alveoli, causing bronchointerstitial pneumonia. Early stages may show intracytoplasmic inclusions and the resulting exudate is predominantly neutrophilic.
Signalment
This affects any bovid of any age, but most commonly calves or cattle housed over winter.
Clinical Signs
This virus may cause rhinitis of cattle when acting alone and with secondary infections may cause signs such as coughing and nasal discharge. If involved in calf pneumonia complex, then signs relating to that will also be seen such as dyspnoea, coughing, increased respiratory rate and general malaise.
Diagnosis
In many cases, history and clinical signs are diagnostic, especially when in complex with other disease. If the agent is acting alone, many cattle will not show any clinical signs.
Diagnosis can be made from diseased lung tissue from dead animals or centrifuged cells from lung lavage. The virus is too fragile for cell culture isolation (often inactivated in transport). Antigen detection by immunocytochemistry for intracytoplasmic viral inclusions containing labelled viral protein can be performed. Serology can also be performed and a 4-fold rise in ELISA antibody in paired serum samples from several animals is indicative of the disease. A first, acute phase sample should be taken and another sample taken around 2 weeks after this (convalescent stage).
Positive confirmation lies in a Fluorescent Antibody Test (FAT) to the specific virus on frozen sections of tissue.
Treatment and Control
Treatment can be given to help secondary bacterial infections.
Control measures include improving managemental factors, such as using all-in all-out systems, preventing mixing of groups of stock and increased ventilation in housing. Preventing overcrowding, humidity and stress are key factors. In calves it is important to ensure passive transfer occurs as a lack of colostrum will greatly increase the risk of disease.
Some vaccination does occur and is available in the UK. Immunity does not last and re-infection is common.
References
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
Bridger, J and Russel, P (2007) Virology study guide, Royal Veterinary College
Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition), Merial
Radostits, O.M, Arundel, J.H, and Gay, C.C. (2000) Veterinary Medicine: a textbook of the diseases of cattle, sheep, pigs, goats and horses, Elsevier Health Sciences