pathogenesis of TB Flashcards
what are mycobacteria species?
these are obligate aerobes and facultative intracellular pathogens, usually infecting mononuclear phagocytes
how is TB spread?
airborne infection by respiratory droplets
not everyone who is infected develops the disease, what is the outcome dependent on?
the host’s immune system
what is the pathogenesis of primary TB initial stages?
Inhaled organism is phagocytosed and carried to hilar lymph nodes
once inhaled, alveolar macrophages ingest the bacteria; the bacilli then proliferate inside the macrophages and cause the release of neutrophil chemoattractants and cytokines
This results in an inflammatory cell infiltrate reaching the lung and draining hilar lymph nodes.
Macrophages present the antigen to the T lymphocytes causing a cellular immune response.
This results in a delayed hypersensitivity type reaction, which leads to tissue necrosis and formation of a granuloma
what is the pathogenesis of primary TB healing stage?
The caseated areas heal completely and many become calcified.
Some of these calcified nodules contain bacteria, which are contained by the immune system (and the hypoxic acidic environment created in the granuloma) and may lie dormant for many years.
what is the pathogenesis of latent TB?
the immune system contains the infection and the patient develops cell-mediated immune memory to the bacteria.
what is the pathogenesis of reactivation TB? (secondary TB)
The majority of TB cases are due to reactivation of latent infection
usually because the patient is immunocompromised
