patho

• Faculty of veterinary system
• Veterinary medicine program
• Bacterial diseases (2)
• Date


  16/4/2024
• Dr: Mohamed M.M. Metwally
• Professor of veterinary pathology
• Tuberculosis (TB)


  A chronic, rarely acute, contagious, granulomatous, debilitating disease of mammals characterized by the formation of tubercles in lungs and different organs
• Mycobacterium species


  • More than 170 species, most of which are environmental organisms
• All Mycobacterium types may produce infection in host species other than their own
• Main recognized types of the Mycobacterium tuberculosis complex (mammalian tubercle bacilli)


  • M tuberculosis
  • M canettii
  • M bovis
  • M caprae
  • M pinnipedii
  • M microti
  • M mungi
  • M suricattae
  • M africanum
  • Dassie bacillus
  • Chimpanzee bacillus
• Mycobacterium avium complex


  • M avium avium (avian tubercle bacilli)
  • M avium hominissuis (isolated from humans, swine, and other mammals)
  • M intracellulare
• M tuberculosis


  The most host-specific; it produces progressive disease only rarely in animals other than humans and nonhuman primates (mainly dogs, pigs, cattle, and elephants)
• M bovis


  Can cause progressive disease in many mammalian species, including humans
• M caprae


  An organism closely related to M bovis, has been isolated from humans, goats, cattle, and several wildlife species
• M avium avium


  The species of most importance in birds; however, it has a wide host range and is also pathogenic for pigs, cattle, sheep, deer, mink, dogs, cats, certain exotic hoofed animals, and some cold-blooded animals
• M avium hominissuis


  The cause of TB in immunocompromised humans, swine, and other animals
• Pathogenesis Pathway


  1. Infection through inhalation, ingestion, intrauterine and coital methods

  2. Bacterium trapped in respiratory mucosa, phagocytosed by macrophages

  3. If macrophages fail to destroy bacteria, they multiply and initiate infection

  4. Bacteria spread aerogenously and via lymphatics

  5. Primary (Ghon) complex forms

  6. If not contained, bacteria disseminate via lymph and blood

  7. Miliary tuberculosis can develop

  8. Post-primary infection (secondary tuberculosis) can occur if immunity declines
• Lesions of TB in bovine

  • Miliary tuberculosis (hematogenous infection)
  • Chronic nodular tuberculosis (inhalation infection)
  • Tuberculous bronchopneumonia (inhalation infection)
  • Bovine tuberculosis pleurisy and peritonitis (pearl disease and grapes disease)
  • Bovine intestinal tuberculosis
• Miliary tuberculosis


  • Multiple young tubercle nodules appear as small, grayish-white, firm, difficult-enucleated, millet-like tubercles
  • Granulomas consist of central aggregation of tuberculous bacilli or caseation surrounded by macrophages, epithelioid, and Langhan's giant cells besides lymphocytes surrounded by a thin rim of fibrous connective tissue at the periphery
• Chronic nodular tuberculosis


  • Old tubercle nodules appear as grayish-white or yellow, hard, difficult enucleated pea or bean-like tubercles
  • Granulomas consist of central caseation and calcification surrounded by macrophages, epithelioid, and Langhan's giant cells besides lymphocytes encapsulated by fibrous connective tissue
• Tuberculous bronchopneumonia


  • Nodules in the bronchi are either closed (bacilli remain in the tubercle) or opened (lesions reveal cavitations and bacilli come out)
• Bovine tuberculosis pleurisy and peritonitis


  • Pearl disease: small rounded grayish elevated and velvety tubercles in the pleura or peritoneum
  • Grapes disease: clusters of white tubercles (grapes-like) in the pleura or peritoneum
• Bovine intestinal tuberculosis


  • Begins as the pneumonic form and spreads to the intestine by coughing up and swallowing sputum, hematogenous or lymphatic spread, or less commonly ingestion
  • Associated with mucosal ulceration overlying Peyer's patches due to vasculitis, thrombosis, and ischemia
• Clinical notes on TB in different species

  • Bovine: Calcification is typical, affects any organ
  • Sheep and goats: Lesions similar to cattle but calcification not common
  • Equine: Productive form with little connective tissue and softening of the center, rare calcification
  • Dogs: Exudative form similar to liquefactive necrosis
  • Birds: Extensive caseation without calcification, deficient cellular elements and connective tissue
• Intradermal tuberculin test


  The single most important diagnostic test for TB
• Johne's disease (Paratuberculosis)


  Chronic granulomatous enteritis of ruminants caused by Mycobacterium avium ssp. Paratuberculosis, characterized by persistent diarrhea, progressive weight loss, debilitation, hypoproteinemia, thickening and corrugation of the intestinal mucosa, and eventually death
• Johne's disease pathogenesis


  1. Ingestion

  2. Intestine

  3. M cells and enterocytes

  4. Peyer's patches

  5. Survival in macrophages/dendritic cells

  6. Long delay (12 months or longer)

  7. Granulomatous enteritis and mesenteric lymphadenitis
• Johne's disease lesions in cattle

  • Chronic segmental diffuse (lepromatous) granulomatous enteritis with thickened intestinal wall, rough corrugated mucosa, and multiple ulcerations
  • Mesenteric granulomatous lymphadenitis, lymphangitis, and lymphangiectasia
  • Aortic and endocardial intimal mineralization
• Johne's disease lesions in sheep, goats and deer

  • Nodular (tuberculoid) granulomas in the intestines, lymphatics, and lymph nodes, sometimes mineralized
• Diarrhea does not occur in sheep and goats (except pygmy goat develop explosive diarrhea and die unexpectedly)
• Johne's disease is one of the most important diseases facing the dairy industry
• Johne's disease progression


  • Infection acquired early in life, often soon after birth, but clinical signs rarely develop in cattle less than 2-year-old
  • Tissue specificity to ileocecal intestine related to greatest concentration and availability of iron in tissue macrophages
  • Bacteria disrupt phagosome-lysosome fusion and block degradative actions of lysosomes
• Mechanisms of injury in Johne's disease

  • Death of cells of the monocyte-macrophage system and of all cell populations in the lamina propria of intestinal villi
  • Death of the epithelial cells of mucosa of the small intestine
• Caseous lymphadenitis (Pseudotuberculosis)


  Chronic suppurative lymphadenitis affecting sheep and goats (occasionally cattle, horses, and camels) caused by Corynebacterium pseudotuberculosis, characterized by enlargement and suppuration of one or more lymph nodes, and occasionally other organs

  
• Caseous lymphadenitis pathogenesis


  1. Infection by skin wounds, and less commonly across the mucous membranes via inhalation or ingestion

  2. Bacteria traffic to regional lymphoid tissues

  3. Acute inflammation

  4. Bacterial toxins evade leukocyte-based destruction

  5. Caseating lymphadenitis

  
• Caseous lymphadenitis lesions


  • Enlarged and firm lymph nodes (mainly prescapular, prefemoral, mediastinal, bronchial, and supramammary)
  • Cut sections show onion-like lamination of fibrous connective tissue alternate with caseated friable mass
  • Whitish-yellow or greenish-yellow pus surrounded by connective tissue capsule
  • Microscopically, central caseous necrosis and calcification surrounded by macrophages, epithelioid cells, and lymphocytes encapsulated by fibrous tissue
• Multiple abscesses in the internal organs may be present in caseous lymphadenitis
• Chronic weight loss or emaciated carcasses present in severe cases of caseous lymphadenitis
• The three types of inflammation are acute, chronic, and granulomatous.