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What are the 3 major factors that play into development of BRD (or any respiratory disease for that matter)?
environmental stresses--> viral infection--> bacterial infection
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How does stress predispose animals to viral infection?
stress--> increased cortisol--> cortisol is an immunosuppressant
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What are the 2 major mechanisms of viral infection associated with shipping fever?
epithelial damage (cytolytic epithelial cell death, loss of cilia, change in surfactant--> decreased function of mucociliary elevator), immunomodulation (reduced function of neuts and macs and adaptive immunity)
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What is the most important aspect of pathogenesis of BRD complex that leads to severe morbidity and death?
virus infection to predispose to secondary bacterial infection
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What are the major primary viral agents associated with BRD complex? (6)
bovine herpesvirus-1, parainfluenza-3, BRSV, BVDv, bovine adenovirus, bovine coronavirus
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What are the gross lesions associated with uncomplicated bovine viral pneumonia? (3)
diffusely non-collapsing, rubbery to firm lungs (bronchointerstitial or interstitial pneumonia), interstitial edema and/or emphysema, rhinitis and tracheitis (only if BHV-1)
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How does secondary bacterial pneumonia arise with BRD complex?
viral pneumonia lowers defenses--> commensal bacteria of airways shift to pathogenicity as opportunistic pathogens--> high morbidity and mortality
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What are the major secondary bacterial agents associated with BRD complex? (6)
Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, Mycoplasma bovis, Truperella pyogenes, Bibersteinia trehalosi
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What bacteria have LPS (3), and what are the consequences of LPS in the body? (2)
M. haemolytica, P. multocida, B. trehalosi; LPS induces endothelial damage (endotoxemia) and is proinflammatory
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What bacteria have lipooligosaccharide (1), and what are its effects in the body? (2)
H. somni; endothelial damage and proinflammatory [ sidenote: H. somni causes emboli and hemorrhages in the brain]
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What bacteria have leukotoxin (2), and what are its effects in the body? (2)
M. haemolytica and +/- B. trehalosi; causes inflammatory cell necrosis and apoptosis
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What are gross lesions associated with secondary bacterial infection of the lungs with BRD complex? (4)
cranioventral distribution; firm, dark red to tan parenchyma +/- exudate; pleural effusion and fibrin indicative of M. haemolytica and H. somni
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What is a critical point of intervention for controlling BRD complex in calves?
modulating stress
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