Pathology

• Organ-specific inflammation


  Inflammatory processes vary according to the organ system affected
• Variations in organ-specific inflammation


  • Distribution of inflammation within the organ
  • Various cell types involved
• Inflammation of joints: infectious arthritis

  1. Inflammation may arrive in the joint via the bloodstream

  2. By spread from bone

  3. By spread from periarticular tissues

  4. By direct penetration [including poor aseptic sampling technique or trauma]
• Inflammation of joints: non-infectious arthritis

  • Degenerative joint disease is an immune-mediated process important in adult animals (e.g. dogs)
  • Inflammation predominantly involves lymphocytes and plasma cells and is centred on the synovial membrane
• Inflammation of the lung: pneumonia

  1. Airborne agents - bronchopneumonia: Infectious droplets tend to deposit in the cranio-ventral portions of the lobes, inflammation is initiated and centred upon the airways, mainly bacterial

  2. Haematogenous agents - interstitial pneumonia: Distribution tends to be throughout the lung, not favouring any area but may be patchy, especially viral infections, microscopy reveals thickening of alveolar walls
• Chronic lung infections such as mycoplasmosis

  Predominant change is peribronchial and peribronchiolar cuffing with lymphocytes, can form lymphoid follicles
• Inflammation of the alimentary tract: gastroenteritis/colitis


  • Infections are generally controlled by the gut associated lymphoid tissue, continuous movement of ingesta and antimicrobial peptides
  • In mild infections, the inflammation is usually catarrhal, particularly in the large intestine
  • More severe infections may damage the structure of the mucosa resulting in repair in which the villi are stunted or fused
• Chronic enteritis and malabsorption

  • Chronic enteritis may result in malabsorption with progressive loss of fluid and protein across the inflamed mucosa
  • Johne's disease is an infection causing granulomatous enteritis and malabsorption
  • Inflammatory bowel disease is an inappropriate immune response to dietary antigens or commensal bacteria
• Inflammation of the liver: hepatitis


  • Acute hepatitis is often due to infection, the liver is swollen and hyperaemic with small pinpoint foci of necrosis
  • Chronic hepatitis can result in progressive fibrosis (cirrhosis), an example in horses is ragwort intoxication
• Inflammation of the pancreas: pancreatitis

  • Acute disease can be associated with obesity or abdominal trauma, release of pancreatic enzymes into surrounding fat causes fat necrosis
  • Chronic pancreatitis is seen in the cat and occasionally the horse, causing progressive fibrosis
• Inflammation of the kidney: nephritis

  • Inflammation can arise in the glomeruli, interstitial tissue or the pelvis
  • Nephritis is often chronic at presentation as the kidney has a high functional reserve
• Nephritis and the nephrotic syndrome

  Glomerulonephritis and/or amyloidosis may cause loss of substantial quantities of protein into the urine, leading to generalised oedema and clotting problems
• Inflammation of the urinary bladder: cystitis


  • Cystitis is more common in females than males due to the shorter urethra
  • Bracken fern toxicity in cattle initially causes vascular ectasia, inflammation and haemorrhage, which can progress to transitional cell carcinoma
• Inflammation of the uterus: metritis

  • Inflammation of the uterus in livestock can occur at service (endometritis) or at parturition (severe metritis)
  • Pyometra (pus in the uterus) occurs relatively commonly in bitches and is life threatening
• Inflammation of the mammary gland: mastitis


  Life threatening mastitis occurs shortly after parturition, some organisms can cause gangrenous, acute and chronic forms of mastitis
• Inflammation of the male genital tract

  • Prostatitis (inflammation of the prostate) is common in dogs, may result in abscessation
  • Orchitis (inflammation of the testis) is uncommon, Brucella abortus causes granulomatous inflammation in bulls
• Inflammation of the central nervous system

  • Encephalitis is inflammation of neural tissue of the brain, myelitis is inflammation of the spinal cord, meningitis is inflammation of the meninges
  • Repair in the CNS involves proliferation of glial cells (gliosis)
• Lymphoplasmacytic inflammation in the CNS: perivascular cuffing


  Several layers of lymphocytes and plasma cells around blood vessels in the perivascular space, common in viral infections or immune-mediated disease
• Inflammatory changes in blood samples

  Examination of blood cell counts and blood smears is a valuable aid in the diagnosis of different types of inflammation and underlying disease processes
• Inflammatory cells in blood: neutrophilia


  Increased numbers of neutrophils in the blood, associations include purulent foci, pyogenic bacterial infections, necrosis, fungal infections, corticosteroids, excitement/stress
• Cells of acute inflammation: band neutrophils


  In severe acute inflammation, immature neutrophils (band neutrophils) may be released from the bone marrow, indicating a 'left shift'
• Inflammatory cells in blood: neutropenia

  Reduced numbers of neutrophils circulating in the blood, associations include Gram-negative infections, factors that destroy neutrophils in the bone marrow, malignancies
• Inflammatory cells in blood: eosinophilia and eosinopenia

  • Eosinophilia - increased eosinophils, associations include parasitism, hypersensitivity, breed predispositions
  • Eosinopenia - reduced eosinophils, associations include corticosteroids
• Inflammatory cells in blood: lymphocytosis and lymphopenia


  • Lymphocytosis - increased lymphocytes, associations include lymphoid neoplasia, chronic infections, fear/excitement
  • Lymphopenia - reduced lymphocytes, associations include viruses, radiation, corticosteroids
• Inflammatory cells in blood: plasma cells and monocytes


  Plasma cells rarely observed in blood, monocytosis - increased monocytes, associations include chronic infections, haemolytic anaemias
• Bacteraemia


  Transient presence of non-pathogenic bacteria in the bloodstream, usually cleared by phagocytes with no detrimental effect
• Septicaemia


  Pathogenic bacteria in the bloodstream, can present as severe multisystemic disease and/or sudden death due to release of bacterial toxins causing circulatory collapse