Understanding the dynamics of Salmonella infections in dairy herds: a modelling approach

Xiao, Yanni; Bowers, Roger; Clancy, Damian; French, Nigel P.

doi:10.1016/j.jtbi.2004.09.015

Cited by 38 publications

(52 citation statements)

References 31 publications

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“…Dublin from our study were in accordance with those obtained in young dairy calves [14]. R 0 was somewhat smaller than most R 0 values calculated in Xiao et al [24] but theirs were based on an unknown transmission parameter.…”

Section: Discussionsupporting

confidence: 91%

“…There is evidence that clinical episodes and shedding of Salmonella recur periodically, at intervals of several months, before disappearing from the farm environment 1 [2,3,9]. Xiao et al [24] and Bergevoet et al 2 developed mathematical and simulation models to understand such dynamics and to simulate control programs, but these models lack reliable parameter estimates for the description of Salmonella dynamics within herds. Quantification of the transmission potential of Salmonella by means of the basic reproduction ratio (R 0 ) can help to improve such modelling studies.…”

Section: Introductionmentioning

confidence: 99%

“…Data were too limited to show possible significant differences in the parameters between the study herds [14]. Xiao et al [24] made an assumption on the transmissibility of Salmonella of 0.006 new infections per animal per day, which is equivalent to R 0 = 5.4 in an average Dutch herd (= 0.006 × 10 days length of infectious period × 90 animals in an average Dutch herd). The aim of our study was 1 to estimate R 0 for S .…”

Section: Introductionmentioning

confidence: 99%

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Transmission ofSalmonellain dairy herds quantified in the endemic situation

et al. 2007

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-Salmonella is a cause of concern in the cattle industry, because it is a zoonosis causing severe invasive infections in humans and because it causes economic and welfare losses in infected herds. In general, cattle in the Netherlands are infected with two types; Salmonella Dublin and Salmonella Typhimurium. Both types cause clinical signs but S . Dublin outbreaks are more prevalent and clinical signs are more severe than S . Typhimurium outbreaks. Our knowledge of the transmission of Salmonella within herds is still limited, while this is an essential component for modelling the success of intervention strategies to control Salmonella. The aim of our study was to estimate the basic reproduction ratio (R 0 ), the number of secondary cases produced from each primary case in a totally susceptible population, for S . Dublin and S . Typhimurium in dairy herds. Serological data were obtained from eight farms with a clinical outbreak of Salmonella, two with an outbreak of S . Dublin and 6 of S . Typhimurium. R 0 was estimated from the serological data of the herds that were in an endemic state of the infection. R 0 across herds was estimated to be 2.5 (95% CI 1.7-9.8) and 1.3 (95% CI 1.1-1.7) for S . Dublin and S . Typhimurium, respectively. The between herd variation was significant and fairly large. The results of the sensitivity analysis showed that the R 0 estimate was not sensitive for changes in the latent, infectious or seropositive periods. The R 0 estimates indicated that the infection would not spread very extensively in susceptible populations under management systems similar to the ones in the study herds.Salmonella Dublin / Salmonella Typhimurium / transmission / dairy cattle

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Section: Discussionsupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Transmission ofSalmonellain dairy herds quantified in the endemic situation

et al. 2007

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“…[consulted 03/04/08]. [35]. Actually, it is a tool to assess ex-ante the efficiency of control measure effects on key factors [16,21].…”

Section: Introductionmentioning

confidence: 99%

ModellingSalmonellaspread within a farrow-to-finish pig herd

et al. 2008

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-Delivery of infected pigs to the slaughterhouse is a major source of pork meat contamination by bacterial hazards to humans. We propose a model of Salmonella spread within a farrow-to-finish pig herd, assuming the prevalence in infected delivered pigs depends on the whole pig life-time and growing process. This stochastic discrete-time model represents both the population dynamics in a farrow-to-finish pig herd using batch management, and Salmonella spread. Four mutually exclusive individual health states were considered: Salmonella-free, seronegative shedder, seropositive shedder and seropositive not shedding carrier, making the distinction between seropositive animals and shedders. Since indirect transmission is the main route of transmission, the probability of infection depends on the quantity of Salmonella in the pigs' environment (Q). A dose effect function is used with two thresholds, assuming saturation in exposure for high Q vs. a minimum exposure for low Q. Salmonella is introduced in an initially Salmonella-free 150-sow herd. Prevalence of shedders and seroprevalence are calculated over time in batches of sows and pigs, and in groups of delivered pigs, composed of pigs from different batches. The model shows very variable seroprevalence over time within a herd among delivered groups, as well as among replications. The mean seroprevalence and the mean shedding prevalence are 19.3% and 13.8% respectively. A sensitivity analysis shows that the Salmonella quantity shed and the maternal protective factor are the most influential parameters on Salmonella prevalence in delivered pigs. swine / Salmonella / epidemiological model / population dynamics / environment

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“…In such a modelling approach, population dynamics of the concerned pathogens and the effect of management of the farmer on the dynamics are simulated using a combination of numerical and analytical techniques. This type of model has been used to investigate the long term behaviour of food-borne pathogens, such as Salmonella infections in livestock, and to develop potentially more effective intervention strategies [26]. Intervention strategies against VTEC O157 can be categorized into antibacterial, probacterial, dietary and management strategies [4].…”

Section: Introductionmentioning

confidence: 99%

Effectiveness of simulated interventions in reducing the estimated prevalence ofE. coliO157:H7 in lactating cows in dairy herds

et al. 2007

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-A transmission model developed to investigate the dynamics of Escherichia coli O157:H7 bacteria in a typical Dutch dairy herd was used to assess the effectiveness of vaccination, diet modification, probiotics (colicin) and hygienic measures as to water troughs and bedding, when they are applied single or in combination, in reducing the prevalence of infected animals. The aim was to rank interventions based on their effectiveness in reducing the baseline prevalence of infected animals in the lactating group. The baseline prevalence of the lactating group and the within-herd prevalence were estimated by the model to be 5.02% and 13.96% respectively. The results show that all four interventions, if applied to all four animal groups or only to young stock, are the most effective and will reduce the baseline prevalence by 84% to 99%. In general, combinations of hygiene (applied in all groups) and one other intervention had the highest effectiveness in reducing prevalence in the lactating group. Vaccination and diet modification show a slightly higher effectiveness than colicin and hygiene.Escherichia coli O157:H7 / on-farm intervention / dairy-beef herd / effectiveness

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Understanding the dynamics of Salmonella infections in dairy herds: a modelling approach

Cited by 38 publications

References 31 publications

Transmission ofSalmonellain dairy herds quantified in the endemic situation

Transmission ofSalmonellain dairy herds quantified in the endemic situation

ModellingSalmonellaspread within a farrow-to-finish pig herd

Effectiveness of simulated interventions in reducing the estimated prevalence ofE. coliO157:H7 in lactating cows in dairy herds

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