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| *If the infection is not contained in the primary complex described above, the mycobacteria can disseminate via lymphatics to other organs and lymph nodes | | *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 | | *This can allow the development of '''miliary tuberculosis''', i.e. numerous small foci of infection in many organs/ tissues |
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| + | *inhalation of ''Mycobacterium bovis'' most common via droplets |
| + | *some tubercle bacilli enter the lymph and travel to the bronchial or mediastinal nodes |
| + | *inhaled bacilli reach the alveoli, set up a focus of inflammation |
| + | *phagocytosed by alveolar macrophages |
| + | *two processes may develop if the animal has not encountered the organism before: |
| + | :- the organism may grow in the phagocytes as intracellular parasites |
| + | ::- produces a nodule of parasitised swollen macrophages known as a tuburculous nodule or a tubercle granuloma |
| + | ::- ultimately, macrophages are killed and infection spreads |
| + | :- the organism may be broken down and some antigens taken up by the immune system |
| + | ::- cell mediated immune system produces cytotoxic T-lymphocytes |
| + | ::- T-lymphocytes can attack and destroy cells harbouring bacilli |
| + | ::- leads to type IV (delayedd type) hypesensitivity |
| + | ::- 'caseous' or cheesy type of necrosis |
| + | ::- if bacterium destroyed, further infection/disease is prevented |
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| + | ====Sequelae==== |
| + | *chronicity |
| + | =====Tuberculosis pleurisy===== |
| + | *caseous lymph node ruptures |
| + | *results from extensive tissue necrosis |
| + | :- if located in lung alveoli, the follicle may rupture into a bronchus, causing spread of the disease to all the other lobules served by that bronchus |
| + | :- if the ensuing necrosis erodes the wall of a large pulmonary vessel, this ruptures into the lung and a fatal haemoptysis might follow |
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| [[Category:Cattle]][[Category:To_Do_-_Clinical]] | | [[Category:Cattle]][[Category:To_Do_-_Clinical]] |