Systematic Veterinary Bacteriology and Mycology

PATHOGENESIS

• In both cattle and sheep, listeriosis can manifest itself in four ways
  • as a CNS infection (meningo encephalitis in adults and meningitis in the young)
  • as abortion
  • as a generalized septicaemia with involvement of the liver and other organs
  • as mastitis in dairy cattle.

Flow Chart

• Silage is commonly implicated in outbreaks of Listeriosis in cattle and sheep. Most pathogenic bacteria require the availability of iron in the host for metabolic activities.
• High iron levels in silage that lead to elevated tissue concentrations of iron may predispose cattle and sheep fed on silage to Listeriosis.
• The pathogenic listeria can penetrate the epithelial barrier in the intestine and multiply in hepatic and spleenic macrophages aided by the haemolysin named listeriolysin O. It leads to septicaemia.
• If the pathogen penetrates through damaged mucosal surfaces to the CNS, via the trigeminal nerve or an alternate route it may penetrate through the dental pulp (when sheep are cutting or losing teeth) to the CNS, resulting in neural form.