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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
*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
====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
[[Category:Cattle]][[Category:To_Do_-_Clinical]]
[[Category:Cattle]][[Category:To_Do_-_Clinical]]