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Describe the pathogenesis of BRD.
- viral infection followed by bacterial infection within 3-5 days
- 1. Attachment
- 2. Evasion of host defense
- 3. Multiplication and/or spread
- 4. Damage to host
- 5. Transmission b/w animals
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What are the viruses involved in BRD? (5)
- IBR- BHV-1
- PI3
- BRSV
- BVDV
- +/- coronavirus
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What are the bacteria involved in BRD? (6)
- Pasteurella multocida
- Histophilus somnus
- Mannheimia hemolytica
- [chronic] Truperella pyogenes
- [chronic] Mycoplasma bovis
- Bibersteinia trehalosi
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Describe the microbial characteristics of M. hemolytica.
- Gram -
- facultative anarobe
- LPS
- leukotoxin
- Sialoglycoprotease
- neuraminidase
- commensal on mucosal surfaces
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Describe the microbial characteristics of Bibersteinia trehalosi. (5)
- Gram -
- facultative anaerobe
- commensal of respiratory tract
- Bighorn and domestic sheep, cattle, goats, wild cervids
- Virulence conferred by leukotoxin
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Describe the microbial characteristics of Pasteurella multocida. (4)
- Gram -
- aerobic, microaerophilic, anaerobic conditions
- commensals of oropharynx
- LPS +/- other virulence factors
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Describe the microbial characteristics of Histophilus somnus. (6)
- Gram -
- facultative anaerobe
- commensals of oropharynx and genital tract
- Lipooligosaccharide (LOS)
- TBP (transferrin binding protein) virulence factor
- hemolysin, capsule
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What syndromes are caused by Histophilus in ruminants? (4)
- BRD
- thrombotic meningoencephalitis
- abortion
- endocarditis
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M. hemolytica causes...
per-acute fibrinous bronchopneumonia
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What is the timeline of Histophilus- associated disease?
usually >30 days in feedlot
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What are antimicrobial options for treating BRD in food animals? (9)
- Beta-lactam: Ceftiofur (Naxcel, Excenel, Excede)
- Macrolides: Tilmicosin (Micotil), Tulathromycin (Draxxin), Gamithromycin (Zactran), Tildipirosin (Zuprevo)
- Fluoroquinolones: Enrofloxacin (Baytril), Advocin (Danofloxacin)
- Amphenicol: Florfenicol (Nuflor, Resflor)
- Tetracycline: Oxytet (LA-200)
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What is the MOA of macrolides?
inhibit protein synthesis by binding the 50S ribosomal subunit
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Describe the pharmacodynamic properties of macrolides.
- Bacteriostatic (maybe cidal?)
- Time-dependent
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What is the spectrum of macrolides?
- Gram + and Gram - aerobes/ facultatives
- EXCEPT: Not good for enterics, anaerobes, Pseudomonas, Enterococcus
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Macrolides have diminished activity under what conditions?
pH < 7 (don't work in abscesses, necrotic debris)
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What are dosing intervals for Micotil, Draxxin, and Zactran?
- Tilmicosin: 72hr
- Tulathromycin: 7 days
- Gamithromycin: 10 days
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What are potential adverse reactions to macrolides?
- Tilmicosin- fatal in humans, alpacas; do NOT give IV
- Erythromycin, Azithromycin- GI disturbances (Equine)
- Any Atb with high Vd- anorexia, GI disturbances
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What are the uses of Erythro, Azithro, Clarithromycin?
- Equine- Rhodococcus pneumonia
- Be careful- causes diarrhea, hyperthermia in foals (d/t motilin activity)
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What is florfenicol labelled for in food animals?
bacterial BRD and Mycoplasma bovis in non-lactating dairy cattle and pigs
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What are the fluoroquinolones labelled for in food animals?
- BRD pathogens and Mycoplasma bovis
- NO ELDU!!!!!!!!!!!!!
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What are the labelled uses for Ceftiofur in food animals?
- BRD, foot rot, metritis (0-14 days post-partum, 2 doses)
- can use ELDU for different indications but MUST follow labelled route, dose, and interval
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What is tetracycline used for in food animals?
- widespread use d/t broad spectrum
- good for Mycoplasma, Treponema (spirochetes), Chlamydia, Rickettsia (gets intracellular)
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