Bovine respiratory disease: approach to an outbreak

o bovis

Contributor(s):

Alexander Corbishley

Peter Down

Synonym(s): Calf pneumonia

Why do calves get BRD?

The mucociliary escalator, leukocytes and anti-microbial molecules (eg antibodies, complement and peptides) work together to protect the respiratory tract from pathogens and restrict commensal organisms to the upper respiratory tract.
Compromise of these defences provides the opportunity for pathogens to colonize the respiratory tract and for commensal organisms to extend deeper into the lower respiratory tract.
The greater the degree of compromise, the broader the range of potential pathogens that are able to successfully invade.
The most pathogenic organisms, often but not exclusively viruses, are usually referred to as primary pathogens and commonly initiate disease.
They can in themselves compromise respiratory tract defence mechanisms and open the door to secondary, usually bacterial, infections.
It is however not uncommon for some bacteria to act as primary pathogens in the absence of a viral infection, when respiratory tract defences are sufficiently compromized or when multiple bacterial species are able to work synergistically to cause disease.