Pathogenesis

 

PATHOGENESIS
  • The diphtheroids infections are characterized by the development of suppurative lesions and clinical manifestations do not develop in the absence of predisposing factors.

Corynebacterium ovis

  • The prevalence of caseous lymphadenitis may be as high as 50% in adult sheep.
  • Some clinically normal sheep may carry the organism in the digestive tract, excrete in the faeces and contaminate the environment.
  • When bacteria enter the host via skin wounds (or tick bite), multiply and are phagocytosed.
  • Phagosome-lysosome fusion takes place. But Corynebacterium ovis multiplies in the phagolysosome and phagocytic cells die.
  • Permeability of local blood vessels increases, encouraging the spread of infection from the initial site to other locations, often-regional lymphnodes.
  • Produces toxins – Phopholipase-D. Abscesses may develop at either primary or secondary sites, eventually rupturing and discharging a thick, caseous pus containing large numbers of viable bacteria. In some instances, lesions become metastatic and, as they increase in number, the thin ewe syndrome develops, resulting in progressive debilitation and death.

Corynebacterium renale

  • Corynebacterium renale is a normal flora in the lower urogenital tract. This group possess fimbriae which allow attachment to the urogenital mucosa.
  • The major predisposing factors that put a cattle at risk are the shortness of the female urethra and the effects of pregnancy and parturition, thus, disease occurs most frequently in mature cows.
  • The vulva may be an important portal entry for Corynebacterium renale into the urinary tract.
  • Bacteria grow readily in urine and ascend (through vesiculo uretharal reflex) to the kidney.
  • Corynebacterium renale has high urease activity. The urease is nephrotoxic and produces pyelonephritis.

Rhodococcus equi

  • Rhodococcus equi may be a commensal in the intestine of horses and it is largely a soil organism.
  • The soil enriched with equine faeces and summer temperatures are favours the rapid multiplication of this bacterium.
  • The disease is usually seen in 2-4 month old foals, possibly due to the decline in maternal antibody at about 6 weeks of age.
  • The main route of infection is by inhalation. Rhodococcus equi is a facultative intracellular pathogen.
  • Its ability to survive, persist in, and eventually to destroy alveolar macrophages is the basis of its pathogencity.
  • It causes granulomatous inflammation and abscesses in the lung tissue.
  • Heavily infected sputum may be swallowed by the affected foal leading to ulcerative colitis and mesentric lymphadenitis.
  • Corynebacteria are pyogenic bacteria causing a variety of suppurative conditions in animals.
  • The main diseases, hosts and natural habitats of the Corynebacteria are
Species
Main host (s)
Diseases
Natural habitat
C. pseudotuberculosis ( Corynebacterium ovis or Preisz Nocard Bacillus )
Sheep and Goats (Non-nitrate reducing biotype)
Caseous lymphadenitis
Skin, mucous membrane and G.I. tract
Horses and Cattle (Nitrate reducing biotype)
Ulcerative lymphangitis
Corynebacterium renale
Cattle
Pyelonephritis and cystitis
Prepuce and semen of asymptomatic bulls, vaginal mucous membrane of heathy cows
Pigs
Kidney abscess
Male sheep
Balanoposthitis
(Pizzle rot)
Corynebacterium cystitidis
Cattle
Severe cystitis, rarely Pyelonephritis
Male genital tract
Corynebacterium pilosum
Cattle
Pyelonephritis
Male genital tract and urine
Corynebacterium bovis
Cattle
Subclinical mastitis
Udder and teat canal of cows
Rhodococcus equi (Corynebacterium equi )
Foals (2-4 months)
Suppurative bronchonephritis
Soil and Faeces of foals and other herbivores
Pigs
Cervical lymphadenitis
Soil

 
Last modified: Monday, 4 June 2012, 5:11 AM