Epidemiology and Infection

Original Papers

The effect of heterogeneous infectious period and contagiousness on the dynamics of Salmonella transmission in dairy cattle

C. LANZASa1 c1, S. BRIENa1, R. IVANEKa1, Y. LOa1, P. P. CHAPAGAINa1a2, K. A. RAYa1, P. AYSCUEa1, L. D. WARNICKa1 and Y. T. GRÖHNa1

a1 Department of Population Medicine and Diagnostic Science, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA

a2 Department of Physics, Florida International University, Miami, FL, USA


The objective of this study was to address the impact of heterogeneity of infectious period and contagiousness on Salmonella transmission dynamics in dairy cattle populations. We developed three deterministic SIR-type models with two basic infected stages (clinically and subclinically infected). In addition, model 2 included long-term shedders, which were defined as individuals with low contagiousness but long infectious period, and model 3 included super-shedders (individuals with high contagiousness and long infectious period). The simulated dynamics, basic reproduction number (R0) and critical vaccination threshold were studied. Clinically infected individuals were the main force of infection transmission for models 1 and 2. Long-term shedders had a small impact on the transmission of the infection and on the estimated vaccination thresholds. The presence of super-shedders increases R0 and decreases the effectiveness of population-wise strategies to reduce infection, making necessary the application of strategies that target this specific group.

(Accepted November 07 2007)

(Online publication January 16 2008)