Respiratory Bacterial Infections - Pathology

()Map CARDIORESPIRATORY SYSTEM (Map) RESPIRATORY SYSTEM INFLAMMATION

In general

• Main clinical expression is as secondary invaders of previously damaged lung tissue due to viral or parasitic involvement or environmental stress
• Some are initial pathogens in their own right while others can damage the tract allowing invasion by more pathogenic types

In Dogs

Infectious canine tracheitis

• See Infectious canine tracheitis
• Synonym: Kennel cough
• Multiple agents implicated

Tuberculosis in dogs

• Dogs are rarely susceptible to Mycobacterium spp. causing tuberculosis in cattle, usually either from human or farm animal source
• Gross pathology:
  • Multifocal nodules, firm, calcified with necrotic centres
  • Usually caudal lung lobes
  • Also granulomatous pleuritis and haemothorax

Nocardiosis

• Caused by Nocardia
• Grossly:
  • Haemorrhagic purulent exudate in pleural cavity
  • Yellow granules on pleural surface
• Possibly caused by penetrating awns of grass
• Mainly in sporting breeds

In Cats

Feline Chlamydiosis

• Persistent respiratory infection caused by Chlamydia psittaci (felis)
• Mild conjunctivitis, serous purulent rhinitis and conjunctivitis, in severe cases mild bronchointerstitial pneumonia - feline pneumonitis

Mycoplasma felis

• Can also cause mild respiratory infection

In Horses

• Overview of equine respiratory disease by N Chanter of the Animal Health Trust, taken from Equine respiratory diseases edited by P Lekeux. Chapters of this book are published by the International Veterinary Information Service (IVIS)

Strangles

• Caused by very pathogenic Streptococcus equi subsp. equi
• Haemolytic streptococci of Lancefield group C are common inhabitants of the equine nasopharynx
• Streptococcus zooepidemicus and S. equisimilis are usually non-pathogenic
• Typically suppurative rhinitis, pharyngitis and lymphadenitis of the lymph nodes of the head and neck that drain the upper respiratory tract, these lymph nodes often rupture and discharge pus 2-3 weeks after the onset of infection
• Infection with Streptococcus equi occurs after contact with contaminated feed, water bowls or an infected carrier horse
• Organism remains viable in environment for months
• Possibility of other sources of infection - in pharynx of in-contact dogs?, guttural pouches of persistently infected horses
• Attaches to nasopharyngeal epithelial cells, then mucosa, lymphatics and lymph nodes
• Multiplies extra-cellularly
• Gross pathology
  • Initial bilateral nasal discharge, serous becoming purulent
  • Catarrhal conjunctivitis may be present
• Less frequently, complications can occur as follows :
  • Purulent inflammation may extent to guttural pouches or lungs, sinusitis
  • Bacteraemia with metastatic abscesses - most often to the mesenteric and mediastinal lymph nodes, less frequently, other organs such as liver, kidney and brain can be involved - Bastard strangles
  • Retropharyngeal abscesses can rupture onto the skin of neck or into the guttural pouch resulting in guttural pouch empyema or chondroid formation - carrier state
  • Purpura haemorrhagica: an acute vasculitis causing urticaria and extensive oedema of ventrum, head and distal limbs
  • Laryngeal hemiplegia due to enlarged retropharyngeal lymph nodes
  • Compression of cranial nerves

• Interview with Professors Josh Slater and Ken Smith providing an interesting insight into the pathogenesis, prevalence and possible prevention of Streptococcus equi infections in horses - listen to Strangles podcast

Streptococcus equi subsp. zooepidemicus

• Causative agent Streptococcus equi subsp. zooepidemicus
• Can infect the respiratory tract (nasal cavity, paranasal sinuses, trachea and bronchi/bronchioles)
• URT infection can be indistinguishable clinically from Strangles, but does not cause suppurative lymphadenitis (cf: S.equi subsp. equi)

Glanders

• Caused by Burkholderia (Pseudomonas) mallei
• Exists in eastern Europe and Asia
• Notifiable in UK
• Characterised by multiple small submucosal nasal nodules which liquefy and ulcerate
  • Cores of neutrophils surrounded by a rim of macrophages and granulation tissue
• In addition may have similar nodules in lungs, lymph nodes and cutaneous lymphatics
• Clinical signs: fever and head/ neck lymphadenitis, rhinitis

Rhodococcus equi

Pyogranulomatous lesions due to Rhodococcus equi (Image sourced from Bristol Biomed Image Archive with permission)

• Causative agent Rhodococcus (Corynebacterium) equi
• Important cause of sever, often fatal granulomatous pneumonia in foals
• Clinical signs include depression, cough, weight loss, respiratory distress, diarrhoea, arthritis, subcutaneous abscesses
• Bacterium survives phagocytosis and multiplies
• Bacterial toxins -> caseous necrosis in lungs -> attracts inflammatory cells -> pyogranulomatous pneumonia
• Grossly:
  • Multiple firm nodules, usually no encapsulation
  • Partial atelectasis
• Histologically:
  • Pyogranulomatous lesions
  • Macrophages with ingested microorganisms in the alveoli
  • Necrosis spreading through parenchyma

In Cattle

Necrotic laryngitis

Necrotising laryngitis (Image sourced from Bristol Biomed Image Archive with permission)

Tracheitis in calf diphtheria (Image sourced from Bristol Biomed Image Archive with permission)

• Synonyms: laryngeal diphtheria, calf diphtheria
• Common disease in cattle, and can occur in swine
• Caused by infection with Fusobacterium necrophorum
• Lesions may also be found in other parts of the oropharynx
• The bacterium usually gains entry through damaged mucosal surfaces e.g. after viral infections or injury following (poor!) use of dosing guns, coarse poor quality roughage
• Results in severe acute neutrophilic laryngitis
• Extensive accumulation of fibrin and necrotic cellular debris on the ulcerated mucosal surface
• Lesions appear as dry plaques of fibrinonecrotic exudate and ulceration on the laryngeal mucosa
• Inhalation of exudate and bacterial organisms may cause bronchopneumonia
• Death may result from toxaemia or asphyxiation
• Also may occur in pigs

CAR bacillus

• Causative agent: Cillia-associated respiratory bacillus
• An unclassified bacteria that can't be grown in culture
• Colonises ciliated epithelium in rodents and ruminants
• Associated with chronic lymphocytic rhinitis, tracheitis and bronchitis
• Clinical disease in rabbits and rodents
• Subclinical disease in ruminants

Pneumonic pasteurellosis

• Synonym: Shipping fever
• Caused by Manheimia haemolytica biotype A serotype 1 (90%) and Pasteurella multocida
• In young, growing cattle
• In clinically normal cattle Mann. haemolytica serotype 2 is present in low numbers, only in nasal cavity and tonsils
• Clinical signs: depression, anorexia, rapid shallow respiration, crusty nose with mucopurulent discharge, serous ocular discharge
• Acute bronchopneumonia and may progress to lobar pneumonia with toxaemia
• Pathology
  • Lobar, cranioventral exudative pneumonia with fibrin, fibrinous pleuritis, areas of coagulative necrosis
• Histology
  • Large numbers of bacteria are usually associated with necrotic lesions

Tuberculosis

Tuberculosis caused by M. bovis (Image sourced from Bristol Biomed Image Archive with permission)

• Caused by Mycobacteruim bovis and M. tuberculosis
• Reside primarily within macrophages where they multiply and result in characteristic granulomatous inflammation (macrophages and giant cells, epithelioid cells)
• Cattle can be infected by inhalation of the organism or through milk
• The primary complex
  • Describes the initial focus of infection at the portal of entry (lungs) plus involvement of regional lymph nodes
  • 90% of cases exhibit the pulmonary form
  • Grossly:
    • Small tubercles in dorsocaudal subpleural areas which progress to larger confluent areas of caseous necrosis
    • Usually start at bronchio-alveolar junction an progress to the alveoli
    • Caseous lesions, may calcify or be encapsulated
    • Multiple foci may coalesce
    • Ulcers in trachea and bronchi due to coughed up bacteria
    • Spreads into pleura
  • Microscopically:
    • Typical granulomatous inflammation
    • Epitheliod and giant cells at centre of tubercles
      • Macrophages with ingested bacteria, forming epithelioid cells - large vesicular nuclei, abundant pale cytoplasm
      • Giant cells, formed by fusion of macrophages, with multiple nuclei
    • Narrow layer of lymphocytes, mononuclear cells and plasma cells at the periphery of the tubercle
    • With time, peripheral fibroplasia and central necrosis develop
• If the infection is not contained in the primary complex described above, the mycobacteria can disseminate via lymphatics to other organs and lymph nodes
• This can allow the development of miliary tuberculosis, i.e. numerous small foci of infection in many organs/ tissues

Contagious bovine pleuropneumonia (CBPP)

Contagious bovine pleuropneumonia (Image sourced from Bristol Biomed Image Archive with permission)

• Caused by Mycoplasma mycoides, small colony variant
• Causes a fibrinonecrotic pneumonia and fibrinous pleuritis
• Also affects caudodorsal areas
• Bronchopneumonia -> lobar pneumonia
• Sequestra are common
• NB: similarity to pneumonic pasteurellosis but CBPP has more pronounced marbled effect
• Interstitial septa are markedly widened by fibrinous exudate and the necrotic areas may have a fibrous capsule
• Large colony variant will cause a similar disease in goats

Enzootic pneumonia of calves

Acute suppurative pneumonia (Image sourced from Bristol Biomed Image Archive with permission)

Calf pneumonia - chronic, with abscesses, fibrosis (Image sourced from Bristol Biomed Image Archive with permission)

• Range of infectious agents together with managemental and environmental stress cause damage to the respiratory tract
• Causes unthriftiness in animals < 6 months old
• Usually the primary pathogen is a virus, secondary pathogens are bacteria and mycoplasmas
• Pathogens:
  • Mycoplasmas
    • Mycoplasmal bronchitis and pneumonia of calves is an important component of the syndrome of enzootic pneumonia
    • On its own causes Mycoplasmal ("Cuffing") pneumonia responsible for bronchitis and bronchiolitis and bronchointerstitial pneumonia
    • It is thought to pick up host antigens in order to prevent recognition by the body defences as foreign
    • In uncomplicated mycoplasma infection, the lesions are generally mild and consist of patchy red/purple areas of atelectasis in the cranio-ventral lung lobes
    • More confluent areas can develop with an underlying bronchointestitial pneumonia and resulting atelectasis
    • M. bovis
      • Most pathogenic
      • Widespread lymphofollicular accumulations which contain germinal centres develop more slowly
      • These lesions can result in narrowing of the bronchiolar lumina - this is the classical lesion of ‘cuffing pneumonia’
    • M. dispar
    • Ureaplasma sp.
  • Viruses
    • Bovine respiratory syncytial virus (BRSV) - can be primary, causes suppression of pulmonary immune response
    • Parainfluenza- 3 (PI3) - can be primary, causes suppression of pulmonary immune response
    • Bovine viral diarrhoea virus (BVDV) - suppression of pulmonary immune response
    • Adenoviruses
    • Calf coronavirus
    • Bovine herpes viruses
  • Bacteria
    • Manheimia (Pasteurella) haemolytica serotype A1
    • Pasteurella multocida
    • Arcanobacter pyogenes
    • Haemophilus somnus
• All transmitted by aerosol and direct contact
• Gross pathology:
  • Consolidation of the cranioventral areas which increases in volume with duration
  • On cut surface, exudate in the main airway of affected lobules with thickening of the surrounding connective tissue
• Micro pathology:
  • Substantial lymphoid tissue around the airways
  • Even to proper follicle formation, some of which may be large enough to compress the lumen
  • Mixed cell exudate in the airway lumen
  • Partial alveolar collapse distal to the compression
  • Alveolar exudate contains a mixture of inflammatory cells
  • Slight thickening of the alveolar walls with lymphocytes

Acute exudative pneumonia

• Pneumonia in very young calves
• Arcanobacter pyogenes is most frequently isolated
• Cranio-ventral distribution

In Sheep

Laryngeal chondritis

Oedema and chondritis in larynx of sheep (Image sourced from Bristol Biomed Image Archive with permission)

• Caused by Fusobacterium necrophorum
• Infection of laryngeal cartilages
• Can be seen in short-necked breed, e.g. Texels, East Friesians and Southdowns
• Leads to extreme respiratory distress
• Laryngeal mucosa is necrotic and ulcerated
• Associated with laryngeal oedema
• Also may occur in young horses and calves

CAR bacillus

• As in cattle

Enzootic pneumonia of lambs

• Caused by Pasteurella (Manheimia) haemolytica, possibly together with Mycoplasma ovipneumoniae
• Mainly in late spring/early summer after environmental stress i.e. handling or moving
• May be acute with producing a fibrinonecrotic bronchopneumonia and associated pleuritis
• Or tending towards chronicity with abscessation and fibrous pleural adhesions
• A septicaemic form (mortality 5%) is reported to follow the stress of movement to new pasture in the autumn in weaned lambs.
• Foci of necrosis containing many bacteria are seen at the site of initial invasion in the pharynx and in the liver
• Meningitis in young lambs and mastitis in ewes are other expressions

Melioidosis (Pseudoglanders)

• Caused by Pseudomonas (Malleomyces) pseudomallei, Closely related to P. mallei in horses
• Causes disease in sheep, goats and pigs, occasionally other species
• Starts as a pyemia and localises in varius tissues, including the lung as abscessation
  • Encapsulated abscesses contain yellow, caseous or creamy pus
• Pneumonia and arthritis are the most common presentation

In Pigs

Atrophic Rhinitis

Severe atrophic rhinitis (Image sourced from Bristol Biomed Image Archive with permission)

• Atrophy of nasal turbinates and distortion and shortening of the snout
• Caused by co-infection of the nasal mucosa with
  • Bordetella bronchiseptica
    • Appears to facilitate colonisation of nasal epithelium by the toxigenic Pasteurella
  • Toxin-producing strain of Pasteurella multocida capsular type D (or sometimes A)
    • Experimental evidence shows that the toxin acts directly on bone cells of the nasal turbinates to cause bone loss, each pathogen can cause atrophy itself but greater damage when together
• Exacerbated by adverse dietary and managemental factors
• In rapidly growing young pigs (4-12 weeks old)
• Clinical signs
  • Progressive facial deformity with rhinitis, catarrhal nasal discharge
  • Sneezing, coughing, can progress to dyspnoea and anorexia

• Gross pathology
  • Overlying skin on shortened snout is thrown into folds
  • Deviation of the snout to most affected side
  • Various loss of turbinate bone, ventral usually more affected
  • Deviation of nasal septum away from affected chamber
  • Inflammatory, haemorrhagic and ulcerative lesions in the nasal mucosa
• Micro pathology
  • Reduction in the amount of bone in the turbinates
  • No osteoid laid down between osteoblasts and existing bone
  • Increased fibrous tissue
  • Non-specific mucosal inflammation

• 2 forms of the disease
  • 'Progressive' atrophic rhinitis
    • Due to infection of the nasal turbinates by P.multocida strains carrying the toxA gene that encodes for an osteolytic toxin. P.multocida adheres poorly to mucous membranes, and therefore requires a predisposing nasal insult to assist colonisation eg: co-infection with B.bronchiseptica or Porcine cytomegalovirus (inclusion body rhinitis)
    • Turbinate bone atrophy is permanent and progressive
  • 'Non-progressive' atrophic rhinitis
    • Due to infection of the nasal turbinates by B.bronchiseptica strains alone, that carry a gene that encodes for a dermonecrotic toxin.
    • Turbinate bone can regenerate by the time of slaughter

• Bordetella bronchiseptica also causes bronchopneumonia

Necrotic laryngitis in pigs

• As in cattle
• Caused by infection with Fusobacterium necrophorum

Enzootic pneumonia of pigs

Enzootic pneumonia of pigs(Image sourced from Bristol Biomed Image Archive with permission)

• Caused by Mycoplasma hyopneumoniae and M. hyorhinis
• Also called mycoplasmal pneumonia
• Major cause of unthriftiness in young pigs
• Pneumonia in weaned pigs
• Cough, reduced growth rate
• Attached to cilia - no mucociliary clearance
• Usually non-fatal unless there is secondary infection (e.g. Pasteurella multocida)
• Gross pathology:
  • Confluent consolidation of the cranioventral lung lobes
  • In other areas there may be small red to grey focal lesions evident which indicate the bronchiolar orientation of the inflammatory process
• Histologically
  • Changes result from a catarrhal bronchointerstitial pneumonia
  • In chronic cases, prominent accumulations of lymphoid cells can be seen around airways and blood vessels

Actinobacillus pleuropneumoniae

• Causative agent: Actinobacillus pleuropneumoniae
• Expolsive outbreaks of pneumonia
• Spread by direct contact and aerosol
• Lesions
  • Largely from toxin produced
  • In diphragmatic lobes of the lungs
• Haemorrhage with fibrinous pleuritis
• Usually localised, sometimes generalised

Pasteurellosis in pigs

• Pasteurella multocida can cause a severe acute fibrinous bronchopneumonia in pigs
• The most significant disease here is that caused by P. multocida secondary to underlying mycoplasma pneumonia, see above enzootic pneumonia of pigs
  • This results in chronic suppurative bronchopneumonia with abscessation and pleuritis
• If there is considerable pleural involvement, it may be indistinguishable from lesions caused by Haemophilus pleuropneumonia (below)
• Also isolated from cases of meningitis and septicaemia in piglets

Contagious porcine pleuropneumonia

• Caused by Haemophilus (Actinobacillus) pleuropneumonia
• Seen mainly between 6wks-6mths of age but will affect any age
• Highly pathogenic strains are capable of initiating disease on their own with high mortality in young pigs
• A fibrinonecrotic bronchopneumonia with pleurisy
• Foci of haemorrhagic consolidation or necrosis, mainly around major bronchi, tend to sequestrate
• Tending to spread throughout all lung lobes: therefore a cranioventral distribution may not be particularly evident

Glasser's disease

• Caused by Haemophilus parasuis
• May cause suppurative bronchopneumonia and pleuritis (as part of polyserositis)
• Stress of mixing, weaning and adverse environmental conditions are predisposing to the disease

Streptococcal pneumonia

• Caused by Streptococcus suis type II
• Zoonotic
• Carried in nasal cavity and lymph nodes of healthy pigs
• Some serotypes may cause embolic pneumonia, others suppurative or fibrinous bronchopneumonia, often in combination with other bacteria

Tuberculosis in pigs

• Pigs are susceptible to the Mycobacterium spp. causing tuberculosis in cattle
• Rarely extends to lungs after haematogenous spread from ingested bacteria causing tubercles with various degrees of calcification, encapsulation and caseation

In Rabbits

Snuffles

• Caused by Pasteurella multocida, less commonly and/or Bordetella bronchiseptica
• Clinical signs (nasal discharge, sneezing) result from an acute to chronic rhinitis

CAR bacillus

• As in cattle