BRSV Bovine Respiratory Syncytal Virus

 

BRSV

Pathogenic Agent

Severe respiratory distress: oral breathing

Bovine Respiratory Syncytial Virus (BRSV)

Etiology

BRSV is frequently isolated in pneumonia of calves and yearlings. Because of its frequent occurrence and tendency to cause infections in the lower respiratory tract, BRSV represents a very important virus in the bovine respiratory disease complex (BRD). Infection is followed by specific clinical signs. Most susceptible to BRSV infection are housed calves aged 4 weeks to 4 months during cold seasons. The method of transmission is not clear, but droplet infection seems to be most likely. BRS virus destroys the ciliated epithelium of the upper airways, predisposing the respiratory tract to further infection. Results of recent research consider the severe clinical signs such as emphysema and edema to be part of allergic reactions to infection.

Clinical Signs

The onset of disease is sudden, and affects livestock with varying severity. Mildly affected calves are noticed by their dry coughing with no or only mild nasal discharge and accelerated respiration. Body temperature increases (to 106 °F/ 41°C ) but there are no signs of general discomfort. Recovery takes about a week. Severe forms of pneumonia caused by BRSV are recognized by depression, anorexia, general discomfort, dyspnea, tachypnea, oral breathing, and fever of 104 to 107,6°F (40 to 42°C ). Auscultation of the lungs reveals characteristic crackling sounds indicating emphysema. Death may occur within a few days in spite of intensive treatment. Recovered animals often fall behind in development and have poor daily gains.

Diagnosis

Lung emphysema and edema

Indications of a BRSV infection are the age of affected animals (4 weeks to about 4 months), fever, absence of nasal discharge, the presence of cold season, and increased incidence of lung edema and emphysema in addition to bronchopneumonic signs.

To confirm your diagnosis, use long, non-breakable but flexible nasal swabs. Collect samples of at least three recently infected animals and send them to your laboratory. Reliable proof of virus can only be provided in a period of 6 days after infection. A fluorescent antibody technique is used by laboratories to detect BRSV in cells. Results will only take a few hours.

Serological tests are not popular because paired serum samples of 10 to 14 days interval have to be compared. But successful treatment requires action in early stages of BRSV infection.

Differential Diagnosis

IBR, Crowding Disease, infectious bovine enzootic bronchopneumonia, acute bovine pulmonary edema and emphysema (fog fever), BVD/MD, bacterial pneumonia.

Control&Prevention

Housed calves are most susceptible to BRSV

Start a vaccination program:

• vaccinate all calves up to the age of 6 months
• vaccinate calves under 6 weeks intranasally with modified live vaccine
• revaccinate after 4 weeks booster annually ...or according to recommendations by your vaccine manufacturer
• vaccinate all new animals
• isolate new animals for at least one week and screen them for diseases
• optimize housing and management conditions
• improve endogenous defense mechanisms in in calves by immunostimulation
• intensify hygiene in order to prevent virus from spreading
• rodent control
• fly control
• disinfection

Treatment

Because of the viral nature of the pathogenic agent, there is only symptomatic therapy. It includes bronchodilatators, spasmolytics, and non-steroidal anti-inflammatory drugs (NSAID). Antihistamines are useful to alleviate the allergic reaction. Recovery is sped up by administration of immunostimulating drugs. Metaphylactic vaccination may help to prevent further spread of disease among livestock. Apply modified live virus intranasally and repeat vaccination after 4 weeks by intramuscular administration of modified live vaccine if local registration allows this procedure. Start antibiotic therapy in case of suspected secondary bacterial infection.

References&Literature

• Blood, D.C., Radostis, O.M., Veterinary Medicine, 1989
• Dyer, R.M., The Bovine Respiratory Disease Complex: A Complex
• Interaction of Host, Environmental, and Infectious Factors,
• Compendium on Continuing Education Vol 4, No7, July 1982
• Dyer, R.M., The Bovine Respiratory Disease Complex: Infectious
• Agents, Compendium on Continuing Education Vol 3, No 10, October 1981
• Fraser, C.M. et al., The Merck Veterinary Manual, 1991
• Mantey, S., Heifer Enemy No.1, Dairy Herd Management, December 1993
• Roenfeldt, S., 5 Diseases you can't ignore, Dairy Herd Management, May 1997
• Smith, B. P., Large Animal Internal Medicine, 1990
• Wren, G., 5 common (but costly) viral diseases of cattle, The Bovine Veterinarian, September 1997