Staphylococcus aureus

S. aureus is a common cause of mastitis in cattle worldwide
Most infections subclinical
Systemic infection can occur with peracute and gangrenous forms
In gangrenous mastitis, the quarter may become necrotic and slough off; alpha toxin causes necrosis of smooth muscle in blood vessel walls, reducing blood flow to the affected quarter, and causes release of lysomal enzymes from leukocytes

Infection of lambs with S. aureus in hill-grazing areas of the UK
Lambs carry S. aureus on their skin and nasal mucosa; infection via skin trauma including tick bites
Ixodes ricinus tick acts as a vector for Ehrlichia phagocytophila, which causes immunosuppression in lambs, predisposing to staphylococcal infection
Acute septicaemia and death or localised abscess formation in many organs
Arthritis, posterior paresis and ill-thrift
Microscopic identification of bacteria in pus and isolation of S. aureus
Prophylactic antibiotics e.g. tetracyclines initiated at 1 week of age may prevent infection
Tick control important

Chronic, suppurative granulomatous condition
S. aureus
Occurs following castration of horses due to infection of stump of spermatic cors
Occurs in mammary tissues of sows
Mass of fibrous tissue containing pus and sinus tracts