[A] 1.61 General pathogenesis of tuberculosis Flashcards
The stages during TB were described by…
- Ranke: In humans
- Nieberle: In animals
Give the stages of pathogenesis of TB
- Primary phase
- Phase of reinfection
- Postprimary phase
- Breakdown phase
- Lung: +++
- GI-tract: +
- Liver: -
- Lung: +
- GI-tract: +
- Liver: ++
- Lung: ++++
- GI-tract:
- Liver:
- Lung:
- GI-tract: ++++
- Liver:
- Lung:
- GI-tract: ++++
- Liver:
- Lung: ++
- GI-tract: ++
- Liver:
- Lung:
- GI-tract: ++++
- Liver:
Unusual sites of the primary process in some species: Cattle
- Genital organs
- Skin
- Udder
Unusual sites of the primary process in some species: Goat & Sheep
GI tract
Unusual sites of the primary process in some species: Horse & swine
Lung
What is shown
Complete primary complex on the lung
Unusual sites of the primary process in some species: Swine, dog, cat
Skin
Cornet rule
- In case of TB, there is a lesion in the lymph node
- There is no primary TB lesion without pathological changes in the lymph nodes
The primary complex
- Infection
- Primary process
- Lesions in the regional lymph node
The primary complex: Varieties
- Complete
- Non-complete
Complete primary complex
- Lesion on the site of the port of entry
- Lesion in the regional lymph node
Draw the complete pathogenesis of TB
Non-complete primary complex
- Sometimes no lesion on the site of the port of entry
- But there is a lesion in the regional lymph node
The primary process following infection…
- Predominantly exudative - In both organs it develops
- Because the host meets the pathogen for the first time
- and there is not seroconversion, no defence is evolved
Progress of the primary complex: possible routes
- Complete healing
- Reaches an inactive quiescent state
- Early generalisation
Progress of the primary complex: Complete healing
- The pathogens are eliminated
- Lesion is absorbed
- Lesion is replaced by connective tissue (scar)
In case of new infection:
- Process starts all over again
- Phase of reinfection
Progress of the primary complex: Inactive quiescent state
- The nodule is demarcated with special tuberculotic granulation tissue
- Pathogens remain infectious in the nodule
- Constant antigen stimulus reaches the organism
- Immunity permanently exists
- Pathogens can get out any time
- The process flushes → Exacerbation
Progress of the primary complex: Early generalisation
- Pathogens get into the circulation
- Infect the organism and metastatise via:
- Haematogenous
- Lympho-haematogenous
- Retrograde lymphogenous routes
- Result:
- Distant tuberculotic lesions in different organs
Give the forms of generalisation
- Acute: Multiple, tiny, miliary nodules
- Protracted (extended): Tuberculotic nodules with different size and age
TB: Primary phase
- Infection
- Development of the primary process
TB: Local process
Either:
- Healing
- with the elimination of bacteria
- Becomes inactive
- Demarcation, but bacteria can survive
- Enter the circulation
- Early generalisation develops
When does immunity of TB develop?
During the progression of the primary complex
Which structured are formed during early generalisation?
Either tubercles or proliferative nodules are formed
TB Early generalisation: What happens during this phase
- Bacteria can re-enter the circulation several times
- Fresher and older lesions can be found next to each other
- Regional lymph nodes are affected
In most species, TB ends in the phase of…
Early generalisation
- Most die in this phase
- Except for cattle
- Reach inactive phase (which can exacerbate (flush) at any time)
- Continues to Chronic TB in organs (via postprimary phase)
Chronic TB in organs
“Isolate TB”
Can develop due to:
- Inactive primary complex
- Inactive early generalisation
- Exogenous superinfection
Chronic TB in organs: Why does no generalisation occur?
The animal has antibodies against the pathogen
- But - The process spreads intra-canalicularly inside an organ
- In the lungs - from acini to acini, from lobules to lobules
- Expectorated content gets to the GI tract (distant metastasis)
Acinous & Acinonodosus TB
- No fresh lesions in the lymh nodes
Postprimary phase:
Chronic TB in organs & Processes leading to this stage
Causes:
- Immunosuppression
- Mycobacteria overwhelm the organism
- Inactive process exacerbation
TB: Breakdown phase
- Pathogens spread
- Late generalisation develops
- Lymph nodes are also affected
- Chronic TB in organs becomes acute
- Extended exudative lesions develop
- Increased intra-canalicular spreading
- Galloping acinonodosous TB (lungs)
Summarise the phases of TB
- Primary phase
- Postprimary phase
- Breakdown phase
