BRSV-MoreThan Just Four Letters On A Vaccination
Bovine respiratory syncytial virus (BRSV) has been recognized
as a pathogen in cattle since 1970. The presence of this
virus in cattle herds is recognized world wide. In the United
States antibody prevalence
has been reported to 65% to 81% in the cattle population.
Aerosolized secretions absorbed through the respiratory
tract is the source of transmission from infected cattle
into susceptible cattle. While bovine cell lines can be
persistently infected, there have been no chronic carrier
cattle demonstrated. Latent infections may occur in calves
infected at birth and may provide an explanation for sudden
outbreaks in calves raised in the isolation of individual
Cattle most susceptible are beef calves six weeks to 13
months of age and dairy calves two weeks to nine months.
In younger calves mortality rates are increased by secondary
bacterial infections resulting in severe exudative, fibrinous,
or suppurativebronchopneumonia. Infections with BRSV have
been implicated as the initiating cause of shipping fever
and other respiratory disease complexes.
Outbreaks of BRSV infection infrequently follow stressful
weather changes. The morbidity of these infections usually
ranges from 0% to 20%. By itself, BRSV can cause acute respiratory
distress. Gross necropsy lesions are severe pulmonary edema
and interstitial emphysema. There are often consolidated
areas in the cranioventral lung lobes accompanied by severe
emphysema and edema of the entire lung but primarily of
the caudal lobes.
Diagnosing BRSV infections starts with recognizing the
clinical signs. Infections tend to be acute with nasal and
ocular discharge, pyrexia, cough, progressive dyspnea, and
occasionally subcutaneous emphysema.
Laboratory diagnosis can be a challenge and diagnosis should
not be made on any one test. Because the virus is so labile,
virus isolation is rarely successful from the tissue of
a post-mortem animal. The best sample for virus isolation
is a tracheal wash or lung lavage.Nasopharyngeal swabs can
also be used with good success. The IFA test is one of the
most rapid, reliable, and sensitive tests currently available
for the diagnosis of BRSV. The best samples for IFA are
the same as for virus isolation. Other tests include immunohisto-chemistiy,
virus neutralization tests, enzyme immunoassays for antibody
detection,enzymeimmunoassays for antigen detection, nucleic
acid detection tests and histopathology. Many of these tests
are not used with very good success but many hold some promise
for the future.
Treatment of BRSV infections consists of a three step regimen.
The first step is supportive therapy. Supportive therapy
consists of keeping the affected animal well hydrated, maintaining
proper electrolyte balance and providing a clean, well ventilated
environment. The second step is to treat affected animals
with antimicrobials to combat any secondary pathogens that
may invade the already compromised lungs. The third step
is the use of anti-inflammatory drugs. Because of
theimmunosuppression of corticosteriods these drugs are
not recommended for use in the treatment of bovine respiratory
disease. Non-steroidal anti-inflammatory drugs (NSAID) are
the drugs of choice. Currently aspirin is the only NSAID
that is approved for use in food animals.
Prevention is the key to dealing with BRSV infections.
Good husbandry and well ventilated housing is mandatory
for the prevention of all respiratory diseases. Vaccination
is another tool available to prevent BRSV infections. Both
modified live vaccines and inactivated vaccines are available.
Both types have pros and cons. Modified live vaccines tend
to stimulate stronger neutralizing antibodies responses.
Both modified live inactivated vaccines stimulate
non-neutralizing antibody and prime T cells in calves.
The presence of maternal antibodies in young calves can
impede the immune response following vaccination with modified
live vaccines. For this reason timing is crucial in the
vaccination regiment. Beef calves should be vaccinated twice
before weaning in order for them to be protected when they
enter the feed lot. Vaccinating dairy calves should be done
with inactivated vaccines or with modified live vaccines
after the maternal antibodies have declined. Maternal antibodies
have usually declined to undetectable levels by six months
- by Fred Froderman, Class of 1997
- edited by Greg Stevenson, DVM,PhD
DVM: The Epidemiology of BRSV Infection. Veterinary Medicine.
Baker, John C.,DVM: Treating BRSV. Veterinary
Medicine.900-902; 1993. Belknap,Ellen.,DVM: Recognizing
the Clinical Signs of BRSV Infection. Veterinary Medicine.886-887;
Bryson, David G.,DVM: Necropsy Findings Associated with
BRSV Pneumonia. Veterinary Medicine.888-893; 1993.
Dubovi, Edward J.,DVM: Diagnosing BRSV Infection: A Laboratory
Perspective. Veterinary Medicine.888-893; 1993.
Kelling,ClaytonL.,DVM: Controlling BRSV Infection in Calves.
Veterinary Medicine. 903-906; 1993.