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| − | [[Image:Tuberculosis M bovis.jpg|right|thumb|100px|<small><center>Tuberculosis caused by ''M. bovis'' (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
| + | #redirect[[Mycobacterium bovis]] |
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| − | *Caused by ''[[Mycobacterium bovis]]'' and ''M. tuberculosis''
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| − | *Reside primarily within macrophages where they multiply and result in characteristic [[Lungs Inflammatory - Pathology#Granulomatous pneumonia|granulomatous inflammation]] (macrophages and giant cells, epithelioid cells)
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| − | *Cattle can be infected by inhalation of the organism or through milk
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| − | *'''The primary complex'''
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| − | **Describes the initial focus of infection at the portal of entry (lungs) plus involvement of regional lymph nodes
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| − | **90% of cases exhibit the pulmonary form
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| − | **Grossly:
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| − | ***Small tubercles in dorsocaudal subpleural areas which progress to larger confluent areas of caseous necrosis
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| − | ***Usually start at bronchio-alveolar junction an progress to the alveoli
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| − | ***Caseous lesions, may calcify or be encapsulated
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| − | ***Multiple foci may coalesce
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| − | ***Ulcers in [[Trachea Inflammatory - Pathology|trachea]] and [[Bronchi and Bronchioles Inflammatory - Pathology#Infectious causes of bronchitis or bronchiolitis|bronchi]] due to coughed up bacteria
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| − | ***Spreads into [[Pleural Cavity & Membranes Inflammatory - Pathology|pleura]]
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| − | **Microscopically:
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| − | ***Typical granulomatous inflammation
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| − | ***Epitheliod and giant cells at centre of tubercles
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| − | ****Macrophages with ingested bacteria, forming epithelioid cells - large vesicular nuclei, abundant pale cytoplasm
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| − | ****Giant cells, formed by fusion of macrophages, with multiple nuclei
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| − | ***Narrow layer of lymphocytes, mononuclear cells and plasma cells at the periphery of the tubercle
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| − | ***With time, peripheral fibroplasia and central necrosis develop
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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
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| − | *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
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| − | *some tubercle bacilli enter the lymph and travel to the bronchial or mediastinal nodes
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| − | *inhaled bacilli reach the alveoli, set up a focus of inflammation
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| − | *phagocytosed by alveolar macrophages
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| − | *two processes may develop if the animal has not encountered the organism before:
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| − | :- the organism may grow in the phagocytes as intracellular parasites
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| − | ::- produces a nodule of parasitised swollen macrophages known as a tuburculous nodule or a tubercle granuloma
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| − | ::- ultimately, macrophages are killed and infection spreads
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| − | :- the organism may be broken down and some antigens taken up by the immune system
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| − | ::- cell mediated immune system produces cytotoxic T-lymphocytes
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| − | ::- T-lymphocytes can attack and destroy cells harbouring bacilli
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| − | ::- leads to type IV (delayedd type) hypesensitivity
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| − | ::- 'caseous' or cheesy type of necrosis
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| − | ::- if bacterium destroyed, further infection/disease is prevented
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| − | ====Sequelae====
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| − | *chronicity
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| − | =====Tuberculosis pleurisy=====
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| − | *caseous lymph node ruptures
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| − | *results from extensive tissue necrosis
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| − | :- 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
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| − | :- 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]]
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