BOVINE RESPIRATORY DISEASE

Bovine Respiratory Disease Complex: BRSV

Bovine Respiratory Syncytial Virus

Etiology
Bovine Respiratory Syncytial virus or BRSV is a common virus that affects cattle around the world and has an economic impact on beef and dairy producers.   It is a RNA virus and is in the paramyxovirus family.  The Virus typically causes respiratory disease that can range in severity from being fatal to the animal not even appearing ill.   This virus is also important because it can predispose the animal to secondary infections.  In this case the virus does not cause any disease symptoms but weakens the immune system so that bacteria, that are generally harmless, can cause disease.

Distribution/Prevalence and Transmission
The disease occurs all around the world and in North America it can be threat in almost all agricultural areas.   The disease is quite common and studies have found that almost 70% of calves going into feedlots have been exposed to the disease.  Although the disease can be found in any age of cattle it is most common to have severe negative effects in younger animals (2-5 months of age).  After the animal has been exposed to BRSV it will build some immunity but this is short lived and afterwards the animal may become re-infected although clinical signs will usually not be severe.  The Virus is transmitted when an animal that is infected sheds the virus in secretions such as nasal discharge and then another animal breaths is some of the virus.  A common example of this would be nose to nose contact.  The virus can also be spread by objects or people that have had contact with infective secretions but the virus does not live long in the environment so this must happen rapidly.

Pathogenisis
Bovine Respiratory Syncytial Virus is a single stranded RNA virusn.  The animal becomes exposed to the virus by breathing in virus particles that are released by other infected cattle.  The virus will then replicate in type 2 pneumocytes and alveolar macrophages, which are two cell types associated with lung epithelium.   The Virus then does two important things, first it reduces phagocytocis of the alveolar macrophages and it causes damage to epithelial cells that can cause death or damage the cells cilia.  These things essentially compromise the immune system of the lungs and make the animal more prone to secondary infections.   This infection will lead to emphysematous bulla, bronchiolitis and interstitial pneumonia.   After an animal becomes infected it will begin to shed the virus and there for be infective by day 3 or 4 and will last up to about day ten.

Clinical Findings & Lesions
Signs of an animal having this are: Difficulty breathing, fever, reduced feed intake and production and nasal discharge.
Lesions produced will be mostly found in the lungs where you will see interstitial pneumonia and edema of the thoracic cavity.

Diagnosis
Diagnosis of this virus is difficult because it is very sensitive to the environment and it may be difficult to maintain good samples.  Samples can include nasal swabs and paired blood samples.  These samples can be sent to a laboratory will they will do tests such as: immunoperoxidase staining, fluorescent antibodies, and enzyme immunoassay.


Treatment and Prevention
There is no real good treatment for the BRSV itself but it may be beneficial to give antimicrobial drugs to prevent a secondary infection.  Also fluids may be beneficial if the animal is dehydrated due to the disease.  
The key to preventing this disease is in prevention.  It is important to remove infected animals from the group if this is possible.  Vaccinations are also useful in preventing the disease if done properly.  There are currently many different intramuscular vaccines that can provide protection.  This protection however, is short lived and animals should be revaccinated often.  Under most systems animals should be vaccinated at branding or processing, again at weaning and then every year following.  Also there are vaccines that are safe for pregnant cows that can be given and these will increase the maternal protection in their calves.  It is best to consult a veterinarian to find a program that fits your operation and will be most effective for you.

References
http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/beef11727
Merck Vet Manual

Produced by Chase Wendorff, Tim Ritson-Bennett, Adam Schierman, Troy Gowan, Justin Rosing for WCVM class project