A mathematical model of Staphylococcus aureus control in dairy herds

An ordinary differential equation model was developed to simulate dynamics of Staphylococcus aureus mastitis. Data to estimate model parameters were obtained from an 18-month observational study in three commercial dairy herds. A deterministic simulation model was constructed to estimate values of the basic (R-0) and effective (R-t) reproductive number in each herd, and to examine the effect of management on mastitis control. In all herds R-0 was below the threshold value 1, indicating control of contagious transmission. R-t was higher than R-0 because recovered individuals were more susceptible to infection than individuals without prior infection history. Disease dynamics in two herds were well described by the model. Treatment of subclinical mastitis and prevention of influx of infected individuals contributed to decrease of S. aureus prevalence. For one herd, the model failed to mimic field observations. Explanations for the discrepancy are given in a discussion of current knowledge and model assumptions.