JPC SYSTEMIC PATHOLOGY

RESPIRATORY SYSTEM

August 2023

P-B12

 

Signalment (JPC #1947581): 2‑year‑old mixed breed steer

 

HISTORY: This steer that was persistently infected with bovine viral diarrhea virus became dyspneic and developed diarrhea, dehydration, and anorexia.

 

HISTOPATHOLOGIC DESCRIPTION: Lung: Affecting approximately 85% of the lung are large, multifocal to coalescing areas of consolidation in which alveoli and bronchioles and to a lesser extent bronchi are filled with an exudate composed of macrophages, degenerate neutrophils, fibrin, increased clear space (edema), occasional hemorrhage, and abundant eosinophilic cellular and karyorrhectic debris (necrosis). Neutrophils and macrophages are often degenerate with streaming nuclei (“oat cells”). Within affected areas and to a lesser extent extending into less affected areas, alveolar septa are expanded up to 4x normal width by similar inflammatory components. Bronchiolar epithelium is frequently hypertrophic and hyperplastic, often piling up to 3 layers thick. The interlobular, perivascular, and subpleural interstitium is expanded up to 3x normal thickness by abundant fibrin and edema admixed with few neutrophils, macrophages, lymphocytes, and plasma cells. Interstitial lymphatics are markedly ectatic (edema) and contain similar cellular infiltrates and fibrin, hemorrhage, and edema. Arteries are frequently lined by hypertrophied (reactive) endothelium. 

 

MORPHOLOGIC DIAGNOSIS: Lung: Bronchopneumonia, suppurative, fibrinonecrotic, acute, multifocal to coalescing, severe, with numerous “oat cells”, mixed breed, bovine.

 

ETIOLOGIC DIAGNOSIS: Pneumonic mannheimiosis 

 

CAUSE: Mannheimia haemolytica (formerly Pasteurella haemolytica biotype A)

 

CONDITION: Shipping Fever, bovine respiratory disease complex (BRDC)

 

GENERAL DISCUSSION:  

• The most important disease of cattle in North America, especially feedlot cattle 
• Gram-negative, non-motile coccobacillus 
• Classic presentation: Pneumonia and/or acute fatal endotoxemia in young cattle following transport from farm of origin to a feedlot

 

PATHOGENESIS:  

• In healthy cattle, relatively non-pathogenic M. haemolytica serotypes S2 and S4 predominate, and pathogenic serotype S1 is present in low numbers  
• Although the exact mechanisms are unknown, some studies suggest that stress and/or concurrent viral infections result in a microenvironmental change which favors increased multiplication and colonization of pathogenic serotype S1 in the upper respiratory tract 
• Reduction in host respiratory immune response (e.g. concurrent viral infection; stressors such as crowding, transport, weaning, etc.,; drastic environmental changes) predisposes cattle to pneumonic mannheimiosis
• Neutrophil mediated inflammation in cattle with BRDC contributes to development of severe disease
• Virulence factors:

• 1. Leukotoxin (Lkt) (Repeats in Toxin [RTX] exotoxin): The most important virulence factor

• Exclusively affects ruminant leukocytes
• Produced by M. haemolytica during logarithmic growth phase
• Composed of 4 genes(lktA, lktB, lktC, and lktD); gene products lktB and lktD required for transport of LKT-A (key virulence gene) from the bacterial cytoplasm to the outer environment
• Effects are concentration-dependent:
  • Low concentration:  (Sublytic affect) Neutrophils undergo respiratory burst and degranulation, stimulate cytokine release from macrophages and histamine release from mast cells, and undergo apoptosis
  • High concentration: ( Lytic affect) induces the formation of transmembrane pores with subsequent oncotic cell necrosis  
  • Lkt binds to beta 2 integrins, which contain CD18 Lkt receptors, found only on ruminant leukocytes
  • In contrast to most bacterial infections where neutrophils phagocytose the offending bacteria, neutrophils recruited to sites of infection with M.haemolytica are most likely lysed by the effects of leukotoxin, hence, this disease is characterized by massive recruitment of neutrophils that are ineffective in killing bacteria  

• 2. Lipopolysaccharide (LPS) (endotoxin):
  • Activates alveolar macrophages (early) and neutrophils (later), inducing them to secrete cytokines (tumor necrosis factor alpha, IL-1 beta), and chemokines (IL-8, ENA, and GRO-alpha), which amplify the inflammatory response 
  • Potentiates effect of Lkt; induces increased expression of beta 2 integrins, which contain CD18 Lkt receptor, on leukocytes
• 3. Polysaccharide capsule (Gram-negative): Aids in attachment, confers resistance to phagocytosis
• 4. Iron-regulated outer membrane proteins: Tbp1 and Tbp2; involved in iron acquisition and possibly adhesion

 

TYPICAL CLINICAL FINDINGS:  

• Depressed, febrile (104*-106* F), and anorexic 
• Dyspnea, productive cough, thoracic pain, mucopurulent nasal discharge, expiratory “grunt”
• Endotoxemia (fever, tachycardia, tachypnea, dyspnea, pale or dark mucous membranes, prolonged capillary refill time, cold extremities) may cause death even in the absence of significant lung pathology

 

TYPICAL GROSS FINDINGS:  

• Fibrinopurulent and necrotizing bronchopneumonia with fibrinous pleuritis and pleural effusion
• Cranioventral distribution 
• Interlobular edema: Septa are distended by fibrin and yellow, gelatinous edema fluid
• “Marbling” appearance is characteristic: Multifocal coagulative necrosis, interlobular interstitial edema, congestion
• Bronchi may contain hemorrhage and/or suppurative material
• Laryngeal epithelial necrosis common in cattle with pneumonia because of traumatic closure of laryngeal folds during dyspnea 
• Peracute infections
  • Red-purple hemorrhagic and infarcted lobules
  • Crisp texture on cut section
  • Abudant, loosely adherent pleural fibrin
• Subacute infections
  • Lobular distribution of lesions
  • Mottled tan-grey suppurative exudate that oozes from small bronchi
  • Purulent or catarrhal exudate  on mucosal surface of large airways
• Chronic Infections
  • Formation of sequestra (necrotic core of firm but friable tissue, enveloped in capsule of fibrous tissue), common as sequelae to coagulation necrosis
  • Bronchiectasis
  • Abscesses
  • Fibrous pleural adhesions

    

TYPICAL LIGHT MICROSCOPIC FINDINGS:  

• Fibrinopurulent bronchopneumonia with necrosis of leukocytes
• Massive infiltration of neutrophils and macrophages, which are often lytic and elongated with nuclear streaming (“oat cells” or “swirling macrophages”)  
• Alveoli filled with edema and fibrin, +/- hemorrhage
• Bronchioles filled with leukocytes, +/- epithelial necrosis (if epithelial necrosis is present, consider underlying viral infection), RBCs, fibrin, edema, and possibly bacterial aggregates
• Foci of coagulative necrosis (some areas represent infarcts due to thrombosis of intralobular blood vessels or direct effects of bacterial toxins / and or leukocyte secretions) often bordered by a basophilic rim of oat cells 

 

ADDITIONAL DIAGNOSTIC TESTS:  

• Aerobic and microaerophilic culture of lungs (postmortem) or transtracheal aspiration, bronchoalveloar lavage, or thoracocentesis fluid (antemortem)
• Immunohistochemistry to identify M. haemolytica 
• Serum antibody determination using bacterial agglutination assay, Lkt neutralization assay, or Lkt ELISA 
• PCR (targeting superoxide dismutase)

 

DIFFERENTIAL DIAGNOSIS:  

• Bacterial pneumonias (often secondary): Bronchopneumonia, purulent (less fibrinous), lack characteristic neutrophil necrosis, differentiate using microbiology culture
  • Histophilus somni (formerly Haemophilus somnus): Suppurative and fibrinous bronchopneumonia, coagulative necrosis with streaming necrotic leukocytes
  • Pasteurella multocida (typically presents with less fibrinous bronchopneumonia)
  • Bibersteinia trehalosi
  • Mycoplasma bovis- Caseonecrotic bronchopneumonia with multiple well delineated necrotic foci filled with caseous material.
  • Trueperella pyogenes (formerly Arcanobacterium spp)
• Mycobacterium bovis (P-B10C): Granulomatous pneumonia (not bronchopneumonia)
• Primary viral pneumonias: Interstitial pneumonia, necrotic and attenuated respiratory epithelium +/-  inclusion bodies and syncytial cells 
  • Bovine respiratory syncytial virus (BRSV, P-V06)
    • Affects cranio-ventral lobes, but lesions are atelectatic, rather than swollen and hard as expected with bacterial pneumonias. Caudal dorsal lobes are voluminous, edematous, heavy, and firm.
    • Bronchointerstitial pneumonia with formation of bronchiolar and alveolar epithelia syncytia 
  • Bovine herpesvirus-1 (BHV-1)
  • Bovine parainfluenza-3 (BPIV-3): 
  • Bovine coronavirus (BCV)

 

COMPARATIVE PATHOLOGY:  

Mannheimia haemolytica in other species:

• Bibersteinia trehalosi (formerly P. trehalosi or Mannheimia haemolytica biotype T) causes pneumonia  and septicemia in lambs 5 months or older  

• Goats: Sporadic cases of acute bronchopneumonia and pleuritis in kids
• Deer: Experimentally demonstrated to cause hemorrhage and congestion, necrosis, degeneration, inflammation, edema in all female reproductive organs (except vagina and cervix), and mild to moderate lesions in the testes, epididymis, vas deferens, and prostate . Occasional cause of bronchopneumonia and septicemia in deer but less common than Trueperella pyogenes or Fusobacterium necrophorum

Other similar bacterial pneumonia:

• Pigs: Gross and microscopic findings in pneumonia caused by Actinobacillus pleuropneumonia (APP, P-B04) are similar to those in pneumonic mannheimiosis of cattle APP produces 4 cytotoxins that are members of the RTX family and cause cytolysis of neutrophils, alveolar macrophages, erythrocytes, endothelium, and epithelium
• Belgian hare: Mannheimia granulomatis, purulent bronchopneumonia (Britton, J Vet Diagn Invest 2017)
• Deer: Mannheimia granulomatis, granulomatous or pyogranulomatous inflammation of the muzzle nasal planum, and upper lip. 

 

REFERENCES: 

1. Aschenbroich S, et al. Mannheimia haemolytica A1-induced fibrinosuppurative meningoencephalitis in a naturally-infected Holstein-Friesian calf. J Comp Pathol. 2013;149(2-3):167-171
2. Azhar NA, Paul BT, Jesse FFA, Chung ELT, Kamarulrizal MI, Mohd Lila MA. Seminal and histopathological alterations in bucks challenged with Mannheimia haemolytica serotype a2 and its LPS endotoxin. Trop Anim Health Prod. 2022;54(5):265.
3. Britton AP, et al. Bronchopneumonia associated with Mannheimia granulomatis infection in a Belgian hare (Lepus europaeus). J Vet Diagn Invest. 2017; 29(4):566-569. 
4. Caswell JL. Failure of respiratory defenses in the pathogenesis of bacterial pneumonia of cattle. Vet Pathol. 2014;51(2):393-409.
5. Caswell JL, Williams KJ.  Respiratory system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6^th ed. Philadelphia, PA: Elsevier Saunders; 2016: 543-544, 562-563, 557
6. Capik SF, et al. Characterization of Mannheimia haemolytica in beef calves via nasopharyngeal culture and pulsed-field gel electrophoresis. J Vet Diagn Invest. 2015;27(5):568-575
7. Dao X, Hung CC, Yang Y, Wang J, Yang F. Development and validation of an insulated isothermal PCR assay for the rapid detection of Mannheimia haemolytica. J Vet Diagn Invest. 2022 Mar;34(2):302-305.
8. Dassanayake RP, et al. Differential susceptibility of bighorn sheep (Ovis canadensis) and domestic dheep (Ovis aries) neutrophils to Mannheimia haemolytica leukotoxin is not due to differential expression of cell surface CD18. J Wildl Dis. 2017; 53(3):625-629. 
9. Ferguson SH,et al. Pathology in practice. Mannheimia haemolytica. J Am Vet Med Assoc. 2011;239(11):1437-1439
10. Fitri W, et al. Mannheimiosis in a Rusa Deer (Rusa timorensis): A Case Report and a Herd Analysis. Research Journal of Veterinary Practitioners. 2017; 5(1): 5 - 11
11. Kamarulrizal MI, Chung ELT, Jesse FFA, Paul BT, Azhar AN, Lila MAM, Salleh A, Abba Y, Shamsuddin MS. Changes in selected cytokines, acute-phase proteins, gonadal hormones and reproductive organs of non-pregnant does challenged with Mannheimia haemolytica serotype A2 and its LPS endotoxin. Trop Anim Health Prod. 2022 Apr 15;54(3):161.
12. Keel MK, Keeler S, Brown J, et. al. Granulomatous Inflammation of the Muzzle in White-Tailed Deer (Odocoileus virginianus) and Mule Deer (Odocoileus hemionus) Associated With Mannheimia granulomatis. Vet Pathol. 2020 Nov;57(6):838-844.
13. Lopez A, Martinson SA. Respiratory system, mediastinum and pleurae. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6^th ed. St. Louis, MO: Mosby Elsevier; 2016:520, 529-531
14. Loy, JD, et al. Development of a multiplex real-time PCR assay using two thermocycling platforms for detection of major bacterial pathogens associated with bovine respiratory disease complex from clinical samples. Jour Vet Diagn Invest. 2018;30(6):837-847
15. Murray GM, et al. Pathogens, patterns of pneumonia, and epidemiologic risk factors associated with respiratory disease in recently weaned cattle in Ireland. J Vet Diagn Invest. 2017;29(1):20-34
16. Omaleki L, et al. Molecular epidemiology of Mannheimia haemolytica and Mannheimia glucosida associated with ovine mastitis. J Vet Diagn Invest. 2012;24(4):730-734
17. Portis E, et al. A ten-year (2000-2009) study of antimicrobial susceptibility of bacteria that cause bovine respiratory disease complex Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni in the United States and Canada. J Vet Diagn Invest. 2012;24(5):932-44.
18. Selwyn AH, et al. Molecular survey of infectious agents associated with bovine respiratory disease in a beef cattle feedlot in southern Brazil. J Vet Diagn Invest. 2018;30(2):249-251
19. Shanthalingam S, et al.  PCR assay detects Mannheimia haemolytica in culture-negative pneumonic lung tissues of bighorn sheep (Ovis canadensis) from outbreaks in the western USA, 2009-2010. J Wildl Dis. 2014;50(1):1-10
20. Singh KJ, et al. Mannheimia haemolytica: bacterial-host interactions in bovine pneumonia. Vet Pathol. 2011;48(2):338-148.
21. Yaman T, Büyükbayram H, Özyıldız Z, et. al. Detection of Bovine Respiratory Syncytial Virus, Pasteurella Multocida, and Mannheimia Haemolytica by Immunohistochemical Method in Naturally-infected Cattle. J Vet Res. 2018 Dec 31;62(4):439-445.
22. Zachary JF. Mechanisms of microbial infections. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6^th ed. St. Louis, MO: Mosby Elsevier; 2016:169-170.

 

 

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