Invited Review: The Role of Cow, Pathogen, and Treatment Regimen in the Therapeutic Success of Bovine Staphylococcus aureus Mastitis

Strain typing of Staphylococcus aureus isolates by means of automated ribotyping revealed a dominant strain (DUP-4025) that responded poorly to treatment and nondominant strains (DUP-4062, DUP-4069) that were associated with cure in a small-scale treatment trial (Tikofsky and Zadoks, 2005).

Simplified representation of the direct and indirect treatment effects. Treatment effect is measured as the reduction in the number of infected cows and it is graphed against the contagiousness of the organism. The graph represents a fictional 100-cow dairy with initially 5 Staphylococcus aureus-infected cows. A 6-mo window is presented in which 50% of the initially infected cows are treated with a 50% cure rate, and the cull risk for all animals is 20%. The actual cure of infected cows is the direct treatment effect. Contagiousness (represents Reproduction Ratio – R₀) is the number of new IMI in the 6-mo window per average Staph. aureus-infected cow present. Indirect treatment effect is the reduction in the number of newly infected cows that can be attributed to the cure of existing infections.