Ruminant Respiratory Pathogens

Primary vs. secondary pathogens

Primary agents establish initial infection; secondary commensals cause disease after the primary insult compromises host defenses

Primary BRD pathogens

BVDV

BHV-1

BRSV

PI3

BCoV

Secondary BRD pathogens

Mannheimia haemolytica

Pasteurella multocida

Histophilus somni

What are the 4 mechanisms by which a primary virus opens the door to secondary bacteria?

URT epithelial damage - mucociliary clearance impaired

Tracheal mucosal damage - mucociliary clearance impaired

Innate defenses suppressed - macs and neutrophils depleted

Acquired immunity suppressed

2 biotypes of BVDV - what's the difference

Cytopathic and noncytopathic

Cytopathic kills cells

BVDV persistent infection (PI) cause

In utero fetal infection with noncytopathic (NCP) BVDV

Role of PI calves in BVDV transmission

Continuous, high-volume viral shedding for life, acting as the primary herd reservoir

BVDV immunosuppressive mechanisms

Impairs neutrophil chemotaxis/killing

Depletes lymphocytes

Compromises alveolar macrophages

Where does primary infection of BVDV occur?

URT/ocular epithelium

Presentation of BVDV

Dry cough

Depression

High fever

Infectious bovine rhinotracheitis is a form of what virus?

BHV-1

Where does IBR replicate?

Upper respiratory and ocular epithelium

Presentation of IBR

High fever

Mucopurulent nasal discharge

Hyperemic nose

Conjunctivitis

Coughing

Depression

What 3 syndromes can BHV-1 cause?

IBR

Repro failure and abortion

Systemic neonatal infection

BHV-1 Latency Site

Trigeminal sensory ganglia (respiratory infection) or sacral ganglia (genital infection)

BHV-1 immune evasion tactics

MHC-I blockade

CD4+ T-cell apoptosis

Macrophage/neutrophil impairment

Lifelong neuronal latency

BRSV primary pathogenesis

Direct cytopathic damage forming syncytia and causing ciliated bronchiolar necrosis

Immunity to BRSV

Maternal antibody, vaccination, and natural infection all only provide partial and transient protection

Classic population affected by BRSV

Weaned calves in the fall

BRSV phases of infection

1. Acute febrile illness - nasal discharge, dry cough, depression

2. Host-mediated immunopathology - interstitial pneumonia, emphysema, fibrin deposition

PI3 pathogenesis

Necrosis of ciliated tracheal/bronchial epithelium

PI3 clinical presentation

Generally mild but predisposes to bacterial infection

BCoV pathogenesis

Respiratory and enteric tropism

Epithelial damage

Influenza D pathogenesis

Replicates in upper and lower respiratory tract

M. haemolytica virulence factor and how it works

Leukotoxin (LktA) - binds CD18 on leukocytes, causing cell lysis or inflammatory degranulation

LPS - drives inflammatory response

M. haemolytica classic lesion

Fibrinonecrotic pleuropneumonia

Cranioventral

P. multocida virulence factor

Antiphagocytic capsule

LPS - inflammation

P. multocida classic lesion

Suppurative/purulent bronchopneumonia

Cranioventral

Histophilus somni causes...

Thrombotic meningoencephalitis (TME)

Myocarditis

Polyarthritis

Septicemia

Fibrinosuppurative pneumonia, cranioventral

H. somni virulence mechanisms

Endothelial cell apoptosis - vasculitis and thrombosis

Biofilm formation

Antigenic phase variation of surface LOS

Is M. bovis a commensal?

No

M. bovis virulence mechanisms

Biofilm formation

Antigenic variation

Suppresses immune response - inhibits neutrophil respiratory burst, promotes lymphocyte apoptosis, induces T cell exhaustion

M. bovis classic lesion

Caseonecrotic bronchopneumonia with well-demarcated necrotic foci

How is M. bovis unique in its disease course?

It is chronic

Mycoplasma bovis treatment

Lacks a cell wall, rendering beta-lactams and cephalosporins completely ineffective

What bacterial BRD pathogen is very resistant to antimicrobials?

H. somni

Primary respiratory pathogen in small ruminants

Mycoplasma ovipneumoniae (a bacterium, unlike viral drivers in cattle)

M. ovipneumoniae virulence mechanism

Impairs pulmonary defenses and predisposes to polymicrobial pneumonia

Exists in a carrier state in subclinical animals

Bibersteinia trehalosi clinical presentation

Acute septicemic pasteurellosis and sudden death in weaned lambs (4-12 months)

Key virulence factor of Bibersteinia trehalosi

Leukotoxin

Small ruminant lentiviruses (OPP / CAE) cause...

Chronic lymphocytic interstitial pneumonia over years

May cause arthritis, mastitis, neurologic disease

Transmission of lentiviruses

Colostrum and close contact

How do lentiviruses persist?

In monocytes/macrophages

SRLV Management Strategy

Serologic testing (ELISA/AGID) and culling; no effective vaccine exists

Orf Virus (Contagious Ecthyma) significance

Zoonotic parapoxvirus causing oral/mucocutaneous lesions; differential for respiratory disease