Pathology and Microbiology of Tetanus

PM Lesions

• No characteristic gross lesion
• No characteristic microscopic lesion

Tetanus

• A bacterial disease of animals caused by the toxins of Clostridium tetani
• Characterized by prolonged spasmodic contractions of muscles, stiffness, and immobilization
• Also known as lock jaw
• Horses are most susceptible, and cattle are the least susceptible
• Etiology: Clostridium tetani, a gram-positive, anaerobe, rod-shaped bacterium that produces toxins
• Spread:
  • The portal of entry is usually through puncture wounds
  • Wounds can be caused by nail-pricks, castration, docking, or shearing, or received during parturition
• Pathogenesis:
  • Sequel to a wound
  • Growth of anaerobic Clostridium tetani
  • Releases neurotoxins
  • The toxin known as tetanospasmin reaches the interspinal site by entering the bloodstream and traveling along nerves to the central nervous system
  • Blocks the secretion of inhibitory neurotransmitters, leading to tetanic spasm of voluntary muscles and ultimately, nerve block and paralysis
• Death occurs from asphyxiation due to fixation of the muscles of respiration

Pathogenesis of Pneumonic Pasteurellosis

• Complex and not clearly understood
• Four virulence factors of P. haemolytica:
  • Fimbriae
  • A polysaccharide capsule
  • Endotoxin (lipopolysaccharide)
  • Leukotoxin
• Capsule inhibits complement-mediated serum killing and phagocytosis and intracellular killing of the organism
• Endotoxin can alter bovine leukocyte functions and is directly toxic to bovine endothelium
• Leukotoxin is produced by all known serotypes and is highly toxic to bovine neutrophils and macrophages
• When destroyed by leukotoxin, release of proteolytic enzymes, oxidant products, and basic proteins which degrade cellular membranes, increasing capillary permeability
• Fluid accumulation in the interstitium of the alveolar wall, alveolar wall necrosis, and pulmonary edema
• Death occurs as a result of hypoxia and toxemia

Clinical Signs of Pasteurellosis

• High fever (105-107°F)
• Oedema in the throat and brisket region
• Dyspnoea
• Ghar-ghar sound on respiration

Pathological Findings of Pasteurellosis

• Widespread petechiae and ecchymoses on mucous and serous membranes
• Oedema of the lungs and lymph nodes
• Oedema of the subcutaneous tissue with gelatinous fluid
• In a few animals, there are lesions of early pneumonia and haemorrhagic gastroenteritis

Microscopic Features of Actinobacillosis

• Presence of colony of organisms
• Palisade of Indian club-like structures surrounded by neutrophils, mononuclear cells, and lymphocytes
• Such lesions are surrounded by fibrous tissue
• Muscle tissue of the tongue is replaced by fibrous tissue

Diagnosis of Actinobacillosis

• Symptoms and lesions
• Isolation of bacteria
• Demonstration of organisms/colony in tissue sections
• Demonstration of rosettes and the absence of Gram-positive organisms
• Differential diagnosis: actinomycosis, nocardiosis, and staphylococcal infections ("botryomycosis")

Actinomycosis

• A disease of cattle, buffaloes, and camels caused by Actinomyces sp.
• Characterized by suppurative osteomyelitis of the mandible and miliary nodules in the lungs
• Also known as lumpy jaw

Microscopic Lesions of Actinomycosis

• Medulla:
  • Circumscribed mononuclear cells in perivascular areas
  • No tissue necrosis
  • Organisms are Gram-positive and demonstrated in tissue sections
  • Micro abscess in the brain
• Systemic infection:
  • More common in monogastric animals
  • Focal necrosis of the liver (characteristic) - Micro abscess in the liver
• Abortion:
  • Common in cattle and sheep
  • Focal hepatic necrosis with stainable organisms seen in foetal liver

Colibacillosis

• Three distinct pathogenetic mechanisms are identified in enteropathogenic Escherichia coli (E. coli)
• Enterotoxic colibacillosis:
  • Caused by colonization of E. coli on the surface of intestinal cells and production of toxins
  • Most common in young piglets, calves, and lambs during the first week of life

Glanders

• Synonym: Farcy, malleus
• A contagious disease of horses, mules, and donkeys (solipeds), usually chronic in nature
• Characterized by formation of nodules and ulcers of the upper air passages, lungs, and cutaneous tissue
• Aetiology: Burkholderia (Pseudomonas) mallei (Actinobacillus mallei)
• Incidence:
  • Horses, mules, and donkeys are highly susceptible
  • Man is moderately susceptible
  • Sheep and goats may be infected
• Transmission:
  • Ingestion
  • Inhalation
  • Through skin invasion
• Pathogenesis:
  • Infection is by ingestion and inhalation of organisms
  • Penetrating the pharyngeal and intestinal mucosa
  • Entering the general circulation and reaching pulmonary capillaries
  • Septicaemic phase with high temperature
  • Forming emboli in the pulmonary capillaries
  • Acute inflammatory reaction in the perialveolar and peribronchiolar area
  • Serous exudate in the connective tissue