JPC SYSTEMIC PATHOLOGY

RESPIRATORY SYSTEM

August 2023

P-B08

 

Signalment (JPC #1795578): A horse

 

HISTORY: This animal had purulent nasal discharge and a chronic cough. The nasal mucosa and skin were ulcerated, and there was thickening of the superficial lymphatics and abscesses in the superficial lymph nodes.

 

HISTOPATHOLOGIC DESCRIPTION: Lung: Approximately 20% of the section is effaced by multifocal, random, variably sized nodules of pyogranulomatous inflammation composed of a central area of eosinophilic cellular and karyorrhectic debris (necrosis) and hemorrhage surrounded by viable and degenerate neutrophils, often epithelioid macrophages, lymphocytes, plasma cells, and rare multinucleated giant macrophages.  Inflammatory cells often extend into adjacent, congested alveolar septa and alveoli where they form an exudate admixed with homogenous eosinophilic material, polymerized fibrin, foamy macrophages, necrotic debris, and hemorrhage.  Multifocally, lumen of alveoli are lined by hyperplastic type II pneumocytes. Multifocally, there are peribronchiolar and perivascular aggregates of lymphocytes, plasma cells, fewer macrophages, rare neutrophils, and edema. The pleural and underlying subpleural connective tissue is expanded up to 0.5mm by edema, fibrin, and low numbers of previously described inflammatory cells.

 

MORPHOLOGIC DIAGNOSIS: Lung: Pneumonia, pyogranulomatous and necrotizing, multifocal, random, moderate, with hemorrhage, type II pneumocyte hyperplasia, and pleural edema, breed unspecified, equine.

 

ETIOLOGIC DIAGNOSIS: Burkholderial pneumonia

 

CAUSE: Burkholderia mallei (formerly Pseudomonas mallei)

 

CONDITION: Glanders, Farcy for cutaneous disease (also Malleus; Droes)

 

GENERAL DISCUSSION:  

• Small, straight to slightly curved, blunt ended, non-motile, unencapsulated, non-spore forming, weakly gram-negative bacillus
• Primarily disease of horses, donkeys, and mules that is characterized by pulmonary, cutaneous, nasal, and lymph node lesions
• Historically important disease in horses used for transportation; has mostly disappeared, still exists in Eastern Europe, Asia, and South America
• OIE-listed, reportable disease; of global concern for equids
• Zoonotic disease and potential bioterrorist threat; considered to be Tier 1 Overlap Select Agent; poses a severe threat to human health and safety and have the potential to pose a severe threat to animals and animal products

 

PATHOGENESIS:  

• Pathways of spread are not fully understood; integument, respiratory, and alimentary systems are portals of entry, while integument and respiratory systems are final destinations
• Transmission via direct or indirect infection from excretions and discharges (especially from skin and nasal mucosa via grooming behaviors)
  • Assumed that bacteria traverses pharyngeal and maybe intestinal mucosa 
  • Conveyed to lungs, almost always causes lung lesions, then hematogenous spread results in nasal, cutaneous, and lymph node lesions
• In nasal mucosa and lungs- bacterium appears to enter and act locally
• Spread to the skin from the nasal mucosa requires a complicated series of steps such as endocytosis, phagocytosis, and leukocyte trafficking (or cell-free bacteremia) to cross the mucosa, spread, and reach and colonize target cells in cutaneous lymphatic vessels
• In alimentary system, ingestion, passage to small intestine, then virulence factors likely facilitate crossing mucus layer
• Virulence factors:

• Development of biofilm and use of adhesins, such as pili, assist in colonizing mucosae
• Type IV pilin-like protein may be involved in the adherence of the bacterium to target cells
• In macrophages and mucosal epithelial cells, type III and IV secretion systems appear to be involved in cell invasion, actin-based motility, and transfer across cell membranes from cell to cell
• Surrounded by capsular polysaccharide antigen that blocks phagocytosis or lysosome fusion
• BpaB protein is involved in adherence to target cells and biofilm formation (Zimmerman Vet Pathol. 2018)

 

TYPICAL CLINICAL FINDINGS:

• Fever, respiratory signs (mucopurulent nasal discharge, nasal ulcers)
• Painful and enlarged submaxillary lymph nodes
• Skin nodules on the legs and abdomen
• Death caused by septicemia

 

TYPICAL GROSS FINDINGS:  

• Nodular lesions in lungs
  1. Generalized pinpoint to 2cm pyogranulomatous nodules throughout lung with central areas of liquefactive necrosis
• Ulcerative and nodular lesions of skin and respiratory mucosa
  1. Nasal lesions unilateral, with copious purulent green-yellow exudate, leaves crateriform ulcer that heals to form a white stellate scar
  2. Pharynx, larynx, trachea
• Cutaneous lesions (Farcy)
  1. Nodules/ulcers that follow lymphatic vessels; raised beaded appearance; rupture due to trauma or pressure necrosis from exudate

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Lung: Pyogranulomatous nodules throughout lung
  1. Central core of neutrophils, often with necrosis of neutrophils and liquefaction of tissue, and peripheral rim of epithelioid macrophages and fibrosis
  2. Proportions of neutrophils, macrophages, fibrosis, and mineralization vary
• Nasal lesions: Nodular submucosal inflammation with inner core of neutrophils and periphery of macrophages; mucosal ulceration
• Skin: Purulent lymphangitis with extensive leukocyte necrosis and lymphadenitis

 

ULTRASTRUCTURAL FINDINGS:

 

ADDITIONAL DIAGNOSTIC TESTS:  

• Mallein test: Intradermal injection of a glycoprotein produced by B. mallei elicits a local or systemic hypersensitivity in sensitized animals (like a tuberculin test); the usual site for injection is the palpebral; swelling and pus‑forming inflammation of the conjunctiva indicates a positive test
• Serology (complement fixation), bacterial culture
• BpaB protein is a useful target for IHC staining infected cells in naturally infected horses (Erdemsurakh et al, Vet Pathol. 2020)

 

DIFFERENTIAL DIAGNOSIS:

Cutaneous form (Farcy):

• Epizootic lymphangitis (Histoplasma capsulaturm var. farciminosum): Disease of the tropics/subtropics; high numbers of yeast in lesions
• Ulcerative lymphangitis (Corynebacterium pseudotuberculosis): Gram‑positive, small, pleomorphic rods, nonmotile; “pigeon fever”, “dryland strangles”
• Sporothrix schenkii : Uncommon mycosis; cutaneous nodules that often ulcerate and fistulate
• Pythiosis (I-F02): Hyphae with eosinophilic and granulomatous inflammation

Pulmonary form:

• Streptococcus equi subsp. equi: Cervical lymphadenitis with chronic nasal discharge; pulmonary and visceral involvement with “bastard” strangles
• Mycobacterium tuberculosis/M. bovis (P-B10): Tuberculosis; typical pulmonary tubercles with acid fast organisms (uncommon in horses)
• Equine herpesvirus-1 (P-V10): Equine viral rhinopneumonitis 
• Equine influenza virus
• Rhodococcus equi (P-B06): Pyogranulomatous pneumonia
• Melioidosis (B. pseudomallei) causes disease in rodents, dogs, cats, and horses; suppurative acute lesions; granulomatous chronic lesions; embolic pneumonia 

 

COMPARATIVE PATHOLOGY:  

Burkholderia mallei in other species:

• Humans are susceptible; potential biological weapon
• Natural disease also occurs in carnivores, sheep, goats, ungulates, dromedaries; cattle and pigs more resistant
• Laboratory animal models:

• Mouse and marmosets used to demonstrate in vivo expression of BpaB virulence factor via immunohistochemistry (Zimmerman, Vet Pathol. 2018)                                                

 

Burkholderia pseudomallei: Melioidosis

• In far north Australia, causes disease in marsupial species
• Important pathogen of managed cetaceans and pinnipeds in Asia; reported in Pacific bottlenose dolphins, Indo-Pacific bottlenose dolphins, killer whales, pseudorcas, and Pacific white-sided dolphins
• Two forms: 
  • Acute septicemic form: More common in cetaceans
    • Gross findings: Multiorgan (especially liver, spleen, lung), multifocal, tan to yellow, necrotic foci varying from pinpoint, miliary to several centimeters in diameter; concurrent splenomegaly and lymphadenomegaly with edema
    • Microscopic findings: Small abscesses or poorly organized pyogranulomas 
      • Chronic, debilitating, granulomatous form 
        • Chronic meliodosis with lumbar vertebral osteomyelitis has been reported in a bottlenose dolphin

 

Burkholderia cepacia complex:  

• Cause subcutaneous abscesses and purulent cellulitis in 5 cats (Wong, J Vet Diagn Invest 2018), associated with contaminated chlorhexidine 2% scrub used for cleaning of existing wounds
  • Gross: Subcutaneous abscesses w/draining fistulas
  • Histo: Severe, pyogranulomatous cellulitis with intralesional Gram (-) bacilli
  • Should be a differential for nosocomial infections in veterinary patients
• Typically considered a pathogen of immunodeficient humans or humans with cystic fibrosis

 

References:

1. Caswell JL, Williams KJ. Respiratory system. In: Maxie ME, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. Philadelphia, PA: Elsevier; 2016:573.
2. Constable P, Hinchcliff K, Done S, Grunberg W. Diseases of the Respiratory System. In: Veterinary Medicine: A textbook of the Diseases of Cattle, Horses, Sheep, Pigs, and Goats. Vol 2. 11^th ed. St. Louis, MO: Elsevier; 2017:1026-1028. 
3. Duncan M. Perissodactyls. In: Terio KA, McAloose D, Judy St. Leger J, ed. Pathology of Wildlife and Zoo Animals, Cambridge, MA Academic Press; 2018: 445.
4. Erdemsurakh O, Purevdorj B, Ochirbat K. Pathological and Immunohistochemical Analyses of Naturally Occurring Equine Glanders Using an Anti-BpaB Antibody. Vet Pathol. 2020; 57(6): 807-811.
5. Lopez A, Martinson SA. Respiratory System, Thoracic Cavities, Mediastinum, and Pleurae. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022: 603.
6. Overlap select agents and toxins, 9 C.F.R.  part 121.4 (2005, amended 2017)
7. Stanton JB, Zachary JF. Mechanisms of Microbial Infections. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022: 221-222.
8. St. Leger, J, Raverly S, Mena A. Cetacea. In: Terio KA, McAloose D, Judy St. Leger J, ed. Pathology of Wildlife and Zoo Animals, Cambridge, MA Academic Press; 2018: 558-559.
9. Wernery U, Wernery R, Joseph M, et al. Natural Burkholderia mallei infection in dromedary, Bahrain. Emerg Infect Dis 2011;17(7)1277-1279.
10. Wong JK, Chambers LC, Elsmo EJ. Cellulitis caused by the Burkholderia cepacia complex associated with contaminated chlorhexidine 2% scrub in five domestic cats. J Vet Diagn Invest. 2018;30(5):763–769.
11. Zimmerman S, Long M, Jelesijevic T. Use of immunohistochemistry to demonstrate in vivo expression of the Burkholderia mallei virulence factor BpaB during experimental glanders. Vet Pathol. 2018; 55(2): 258-267.

 

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