A mathematical model of Staphylococcus aureus control in dairy herds

Abstract

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 (R0) and effective (Rt) reproductive number in each herd, and to examine the effect of management on mastitis control. In all herds R0 was below the threshold value 1, indicating control of contagious transmission. Rt was higher than R0 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.

Prevalence, risk factors and multidrug resistance profile of Staphylococcus aureus isolated from bovine mastitis in selected dairy farms in and around Asella town, Arsi Zone, South Eastern Ethiopia

“…Antibiotics on dairy operations are used to treat highly prevalent infections, such as subclinical mastitis, and as a preventive measure during dry cow therapy (Zadoks et al, 2002). Monitoring the emergence of resistant pathogens in animal reservoirs is important particularly for those with zoonotic potential (Normanno et al, 2005).…”

Herd level approach to high bulk milk somatic cell count problems in dairy cattle

“…Many studies have shown an impact of mastitis control programs in reduction of the prevalence and incidence of mastitis (Barkema et al 1998b;Neave et al 1969;Hillerton et al 1993;Hillerton et al 1995;Zadoks et al 2002). Success is particularly easy to achieve in the case of S. agalactiae mastitis (Loeffler et al 1995).…”

“…Control of S. aureus mastitis is often deemed to be difficult, but many herds have been successful in this regard through implementation of the standard mastitis prevention program (e.g. Hillerton et al 1995;Zadoks et al 2002). The standard mastitis prevention program also affects the prevalence and incidence of S. dysgalactiae and S. uberis (Neave et al 1969), regardless of the often used and misleading label of 'environmental streptococci'.…”

“…Treating animals with high SCC is most successful in herds where S. agalactiae is the main cause of mastitis (Loeffler et al 1995), although it can also be considered in herds with mastitis caused by other streptococci (St. Rose et al 2003;Swinkels et al 2005) or S. aureus (Zadoks et al 2002;Barkema et al 2006). Still, some cow-related factors strongly affecting the probability of cure such as previous history of high SCC or CM, parity, stage of lactation, quarter position, and number of infected quarters, should be taken into account before appropriate treatment can be decided.…”

“…The adoption of recommendations and their effect needs to be checked. Consistent attention from veterinarians or herd advisors to udder health management has repeatedly been shown to contribute to improvement of the situation (Hillerton et al 1995;Wilson et al 1997;Zadoks et al 2002). Therefore, a second visit when sufficient new data are available is needed.…”