JPC SYSTEMIC PATHOLOGY

PULMONARY SYSTEM

August 2023

P-B09

 

Signalment (JPC #2012606): Female Hartley guinea pig

 

HISTORY: This guinea pig was from a colony with unusual morbidity and mortality following acquisition from the supplier.

 

HISTOPATHOLOGIC DESCRIPTION: Lung (multiple sections): Affecting approximately 40% of the lung and often centered on bronchioles are large, multifocal to coalescing areas of lytic necrosis characterized by loss of normal tissue architecture with replacement by necrotic cellular debris admixed with fibrin and numerous heterophils with fewer macrophages, lymphocytes, and plasma cells. Heterophils are often degenerate with streaming nuclei (oat cells) and line well-demarcated areas of necrosis. Adjacent alveolar septa are frequently necrotic with replacement by fibrin, edema, hemorrhage, and low numbers of heterophils and macrophages. An exudate composed of previously described inflammatory cells, fibrin, and necrotic cellular debris multifocally fills and often obscures bronchi, bronchioles, and alveoli. The bronchiolar epithelium is often either attenuated with loss of cilia, sloughed into the lumen, or mildly hyperplastic, with piling up to 3-4 cell layers thick. In less affected areas, alveolar septa are multifocally expanded up to five times normal by previously described inflammatory cells, and alveoli contain homogenous eosinophilic fluid (edema) or are dilated and confluent with adjacent alveoli with fragmentation and loss of the intervening septa (emphysema). Focally, the pleura is lined by small numbers of previously described inflammatory cells admixed with fibrin, and mesothelial cells are multifocally hypertrophied (reactive).

 

MORPHOLOGIC DIAGNOSIS: Lung: Bronchopneumonia, necrosuppurative, subacute, multifocal to coalescing, marked, Hartley guinea pig (Cavia porcellus), rodent.

 

ETIOLOGIC DIAGNOSIS: Pulmonary bordetellosis

 

CAUSE: Bordetella bronchiseptica

 

CONDITION: Bordetellosis (epizootic pneumonia)

 

GENERAL DISCUSSION: 

• B. bronchiseptica is a small (0.2 to 0.5 µm by 1.5 µm), motile, gram-negative coccobacillus with an affinity for ciliated respiratory epithelium; normal commensal bacteria of oropharyngeal mucus membranes; opportunist that causes more frequent and more severe disease in polymicrobial infections
• It is an important cause of respiratory disease in guinea pigs of any age, but disease and mortality occur most often in young guinea pigs, particularly during the winter; spread among guinea pigs may be enzootic with occasional epizootics (outbreaks)
• It has worldwide distribution and causes acute, contagious respiratory disease in many domestic and wildlife species; young animals are particularly susceptible
• Interspecies transmission may occur (e.g. rabbit to guinea pig)

 

PATHOGENESIS:

• Incubation period from 1-14 days with a clinical course of one to three weeks  
• Transmitted by close contact, aerosolization, or via fomites > bacteria adhere to ciliated respiratory epithelium > evade immune defenses via virulence factors > replicate among epithelial cilia >ciliostasis (critical event) > colonization > depressed mucociliary clearance and host cell necrosis > mucopurulent tracheobronchitis > +/- mucosal erosion > “dependent settling” via gravity of the bacteria into dependent lung lobes
• B. bronchiseptica causes ciliostasis & reduced clearance of particles with 1 hour of infection; stimulates mucus secretion by 4-8 hours; induces epithelial cytotoxicity at 36 hours by secretion of tracheal cytotoxin

 

VIRULENCE FACTORS:

• The bordetella virulence gene (bvg) operon regulates expression of virulence factors 

• After entering host, a first wave of factors is expressed (FHA, pertactin and fimbrae); FHA and pertactin antibodies are partially protective against disease

• Following attachment to mucosal surface, a second wave of factors is expressed (for motility, iron scavenging, etc)

• Filamentous hemagglutinin (FHA) 

• Adhesive protein àattachment to ciliated epithelium (prevents clearance by cilia)
• May allow adherence to macrophages and neutrophils

• Pertactin – adhesive protein
• Fimbriae – adhesive protein àattachment of the bacteria to ciliated epithelial cells
• Adenylate cyclase toxin (hemolysin) 

• Adenylate cyclase toxin is a member of the RTX (repeats in toxin) family of toxins similar to the leukotoxin secreted by M. hemolytica
• The RTX domain forms pores in host cell membranes, permitting transfer of the adenylate cyclase domain
• Increased cAMP production occurs after entry of the toxin into leukocytes à inhibits phagocytosis & oxidative burst
• May induce apoptosis of macrophages

• Tracheal cytotoxin – Soluble peptidoglycan is secreted by the bacteria and stimulates host cells to secrete nitric oxide, inducing ciliostasis and apoptosis of ciliated epithelial cells, causes mitochondrial bloating, disruption of tight junctions, and damage to ciliated cells; it is NOT directly toxic to tracheal epithelium
  • Dermonecrotic toxin (DNT) - may help bacteria colonize by impairing the mucous layer & ciliated respiratory cells
  • Lipooligosaccharide – A lipopolysaccharide with endotoxin activity found in the bacterial cell wall, prevents antibody action against bacteria
  • Bordetella is also able to enter and survive within non-phagocytic cells which provides nutrients (and evades host defenses)

 

TYPICAL CLINICAL FINDINGS:

 

TYPICAL GROSS FINDINGS:  

• Purulent bronchopneumonia and fibrinosuppurative pleuritis (rabbits):  Cranioventral distribution; multifocal to coalescing, discrete, irregular, reddish-gray areas of congestion and consolidation that may involve multiple lobes; pleuritis occasionally 
• Diffuse bronchopneumonia more common in NHP 
• Mucopurulent or catarrhal exudate within the nares, nasal passages and trachea and often in tympanic bullae (guinea pig)
• Congested conjunctiva; mucopurulent crusts around the eyes

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Suppurative to necrosuppurative bronchopneumonia with marked infiltration of airways and alveoli with heterophils/neutrophils 
• Obliteration of normal architecture
• Occasionally, necrotizing tracheitis
• A dense fibrillar layer covering the respiratory epithelium may be observed using a Warthin-Starry silver stain or a Gram stain
• BALs will show small coccobacilli adhered to cilia of respiratory epithelial cells (rule out mycoplasmosis)

 

ADDITIONAL DIAGNOSTIC TESTS:  

• Bacterial culture using blood agar
• PCR and ELISA

 

DIFFERENTIAL DIAGNOSIS:

Bronchopneumonia in guinea pigs: 

• Streptococcus pneumoniae (pneumococcal pneumonia, P-B07) – fibrinopurulent pleuritis, pericarditis, peritonitis; marked consolidation of affected lung lobes
• Guinea Pig Adenovirus – necrotizing to necrosuppurative, exfoliative bronchitis and bronchiolitis; basophilic, intranuclear inclusion bodies within sloughed epithelium; consolidation of the hilus and cranial lung lobes (see WSC 2016, Conference 8, Case 3)
• Klebsiella pneumoniae (P-B13) – acute necrotizing bronchopneumonia with pleuritis, pericarditis, peritonitis and splenic hyperplasia
• Systemic form of Streptococcus zooepidemicus (cervical lymphadenitis, H-B02) – fibrinopurulent bronchopneumonia, pleuritis, and pericarditis with focal hepatitis, focal myocardial degeneration, and acute lymphadenitis; bilateral enlargement and abscessation of cervical lymph nodes, retrobulbar abscesses, and otitis media

 

COMPARATIVE PATHOLOGY: 

• B. bronchiseptica primarily infects dogs, pigs, guinea pigs, cats, rabbits, and horses; a carrier state may exist in some animals; less commonly infects rats, non-human primates and many wildlife species (opossums, raccoons, ferrets, bears, foxes, squirrels, leopards, seals, sea otters, lesser bushbabies, hedgehogs and koalas) may become infected
• Dogs
  • Infectious canine tracheobronchitis (“kennel cough"; canine infectious respiratory disease (CIRD)):  Mucopurulent tracheobronchitis; more severe disease in polymicrobial infections.
  • Opportunistic infection in cases of canine distemper (P-V01)
  • Canine parainfluenza virus, canine adenovirus-2, canine herpes-1 may permit secondary Bordetella infection
  • Can cause life-threatening pneumonias in puppies
  • Pigs
    • Component of atrophic rhinitis; colonize ciliated epithelial cells (dermonecrotic toxin and adenylate cyclase) allow for Pasteurella multocida (or other agents) to then colonize > lysis of ciliated epithelial and stromal cells of turbinates & concurrent activation of osteoclasts and inhibition of osteoblasts > osteolysis and atrophy of turbinate bone; the effect of both pathogens is more pronounced (synergistic) in co-infection with Bordetella allowing for robust subsequent colonization by Pasturella
  • Turkeys
    • B. avium is the primary agent of turkey coryza; very similar pathogenesis and virulence factors. It causes a high morbidity upper airway disease in flocks that is worsened by coinfection with Pasturella, E. coli, and, Newcastle Disease, and Mycoplasma
    • B. avium can also infect several species of fowl, psittacines, ratites, finches, and domestic songbirds; in cockatiels, it has been associated with lockjaw syndrome (respiratory disease with temporomandibular rigidity at least in part due to extension of sinusitis into surrounding tissues)

 

References:

1. Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: Blackwell Publishing; 2016: 132-133;222-223;271-272. 
2. Caswell JL, Williams KJ. Respiratory system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. New York, NY: Elsevier Limited; 2016:578-579.
3. Chambers JK, Matsumoto I, Shibahara T et al. An outbreak of fatal Bordetella bronchiseptica bronchopneumonia in puppies. J Comp Pathol. 2019; 167: 41-45.
4. Crespo R, Franca MS, Fenton H, Shivaprasad HL. Galliformes and Columbiformes.  In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. London: Elsevier/Academic Press; 2018: 755.
5. Delaney MA, Treuting PM, Rothenburger JL.   Rodentia.  In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. London: Elsevier/Academic Press; 2018:509-510.
6. Matz-Rensing K, Lowenstine LJ. New World and Old World Monkeys.  In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. London: Elsevier/Academic Press; 2018:359.
7. Simmons J and Gibson S. Bacterial and mycotic diseases in nonhuman primates. In: Abee CR, Mansfield K, Tardif S, Morris T, eds. Nonhuman Primates in Biomedical Research: Diseases. 2^nd ed. London, UK: Academic Press; 2012:124-125.
8. Zachary JF. Mechanisms of microbial infection. In: Zachary JF. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Mosby; 2022:217-219; 624-625; 631; 639

 

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