Tuberculosis

TUBERCULOSIS (TB)

Definition

  • TB is a chronic wasting disease caused by an aerobic, acid, fast rod shaped organisms Mycobacterium tuberculosis

Aetiology

M. tuberculosis

man and animals

M. bovis

man and animals

M. avium

domestic and wild fowl pigs, human monkeys TB

M. paratuberculosis

cattle and sheep- JD

M. leprae

human Leprosy


Incidence

  • TB occurs universally in man and animals
  • Bovine TB is wide spread t hroughout the world including India.

Susceptibility

  • Apart from cattle, pigs, monkeys and domestic fowl, TB is not common disease in animals.
  • It has been recorded in camels, deer, antelope, llamas and bears

Transmission

  • Aerogenous or inhalation
  • Ingestion
  • Rarely cutaneous, congenital and mammary

Pathogenesis

  • Due to its ability to escape killing by macrophages and induce delayed type hypersensitivity
  • M.tuberulosis wall is containing several components 1. Cord factor - formation of granuloma 2. Lipoarabinomannan- Secrete TNF alpha-fever, weight loss and tissue damage; interleukin-10- suppress mycobacteria induced T-cell proliferation 3. Complement- CD3 4. M.tuberculosis heat shock protein - autoimmune reactions
  • Development of cell mediated or type IV hypersensitivity to the tubercle bacillus, is probably due to the organism's destructiveness in tissues and also to the emergence of resistance to the organisms
  • Local reaction ( Oedema, hyperaemia and neurophilic infiltration)
  • The tubercular organisms are surrounded and engulfed by neutrophils
  • But cannot kill bacilli
  • In response to the lipid content of the bacili, macrophages are attracted to the area
  • Ingest the dead neutrophils with bacilli
  • Bacilli proliferate in macrophage
  • Collection of macrophage (Nodule) occurs
  • Bacilli killed and lipid substance dispersed into the cytoplasm of the macrophage converted into "epithelioid cells"
  • Macrophages fuse to form Langhans' giant cell with numerous nuclei arranged as horse shoe shaped at the periphery of cytoplasm and together a nodule is formed.
  • A narrow zone of lymphocyte surrouding the lesion beyond which fibroblasts form causing a microscopic tubercle consisting only of cells and is called hard tubercles
  • These tubercles fuse to become larger and macroscopic
  • Due to the toxic action of the organisms the centre of the nodule undergoes necrosis, caseation and calcification and becomes a soft tubercle
  • The Well formed tubercle (granuloma ) consists of the following lesions from within outwards 1.Central calcified blue stained (Haematoxylin &eosin ) area 2. Caseated faint pinkish blue area 3. Zone of necrosis 4. Epithelioid cells 5. Langhans giant cells 6.lymphocytes 7. Zone of fibroblast

Organisms gain entry to lymphatics

From regional lymph node will spread to distant sites

  • Amitotic division of nucleus of epithelioid cells without division of cytoplasm
  • Giant cell (Langhan’s giant cells)
  • Narrow zone of lymphocytes
  • And fibroblast in periphery
  • Small nodules of 1-2 mm diameter are formed
  • Coalescence of tubercle
  • Mycolic acid fraction of lipid is attributed to acid fastness of the organisms

Large nodules

  • Central area become necrotic because of avascularity and toxic action of organism
  • TB spread in body in two stage
  • Primary complex and post primary dissemination
  • Lesion at the point of entry secondary infection
  • eg. Inhalation - Lungs due to endogenous and exogenous reinfection of tissue

Clinical signs

  • Cattle some animals are clinically normal progressive emaciation
  • Erratic appetite, intermittent fever
  • Pulmonary involvement – chronic cough due to bronchopneumonia
  • TB of intestine – diarrhoea
  • TB mastitis – spread through milk
cattle tb

Tuberclosi - Cattle - Emaciation

Pigs

  • TB lesions are confined to lymph nodes of head and neck -TB is cervical lymph nodes – rupture open and discharge purulent material
  • TB meningitis and TB arthritis are common

Horses

  • TB cervical spondylitis and osteomyelitis
  • Stiff neck – inability to eat

Sheep and goat

  • Bronchopneumonia
  • Diarrhoea

Gross lesions

  • Lungs: caseous acinar bronchopneumonia
  • Caseous lobar bronchopneumonia
  • Encapsulated caseous, gritty nodules
  • Hard to cut
  • Trachea and bronchi show ulceration

Pleura and peritoneum

  • lymphogenous route
  • Tubercles – bunch of grapes -pearly disease
  • Thickening
  • Caseous / calcified center with epitheliod cells enclosed by fibrous tissue
  • Mediastinal and bronchial Lymph nodes affected
  • Intestines :In calves- peyer patches-ulcers
  • Other organs like liver kidney, spleen bone, CNS

Mammary gland

3 forms

  • Disseminated miliary TB
  • Lobular infiltrating TB
  • Mastitis tuberculosa contagiosa

Microscopically

  • Buffalo : TB is not characterised by calcification but involvement of retropharyngeal lymph node is fequent
  • Horse : TB lesions one chronic proliferatetive; Caseation and clacification rare
  • Sheep and goat : May get rarly affected by the bovine type with fewer number of foci anrd early calcification
  • Birds : calcification is not a feature
  • Swine : caseo calcarous encapsulated foci mostly affecting Lymph nodes of head, neck, measnetry
  • Dogs and cats : Distinct granulmas with caseous centers

Diagnosis

  • Clinical diagnosis ofTB is possible only after the disease has reachd an advanced stage
  • Radiology is used in human but seldom in animals
  • Demonstration of bacilli by exaination of sputum, milk etc. Ziehl-Neelsen's stain demonstrates acid fast rod shaped organism
  • Tuberculin test
  • For laboratory investigation suspected lesion may be sent in 10 per cent formol saline, milk in sterile containers or pus from lesions
Last modified: Wednesday, 6 June 2012, 1:54 PM