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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Environmental Microbial & Food Safety Laboratory » Research » Publications at this Location » Publication #310549
Title: Invasion and transmission of Salmonella Kentucky in an adult dairy herd using approximate Bayesian computation

Author
item LU, ZHAO - Cornell University
item MITCHELL, REBECCA - Cornell University
item SMITH, REBECCA - Cornell University
item Karns, Jeffrey
item Van Kessel, Jo Ann
item WOLFGANG, DAVID - Pennsylvania State University
item SCHUKKEN, YNTE - Cornell University
item GROHN, YRJO - Cornell University

Submitted to: BioMed Central (BMC) Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/2013
Publication Date: 12/9/2013
Citation: Lu, Z., Mitchell, R.M., Smith, R.L., Karns, J.S., Van Kessel, J.S., Wolfgang, D.R., Schukken, Y.H., Grohn, Y.T. 2013. Invasion and transmission of Salmonella Kentucky in an adult dairy herd using approximate Bayesian computation. BioMed Central (BMC) Veterinary Research. 9:245-251.

Interpretive Summary: Salmonella is a common cause of foodborne illness; approximately 15 out of every 100,000 people in the US are infected with this organism every year. Dairy cattle are known reservoirs for Salmonella but they are often asymptomatic carriers so that the infection does not make the cattle sick. We followed a herd of ~100 dairy cows in Pennsylvania during a period when they were experiencing an outbreak of Salmonella Kentucky. Kentucky is just one of more than 2000 Salmonella serotypes that have been identified. Fecal samples from the cows were collected every 4 to 12 weeks and tested for the presence of S. Kentucky during the course the infectious outbreak. To understand the invasion ability and transmission dynamics of Salmonella Kentucky in dairy cattle, accurate estimation of the key epidemiological parameters from longitudinal field data is necessary. Therefore a specialized computation technique (Bayesian) was used to estimate various infection parameters such as transmission rate, recovery rate and reproduction ratio using data from themulti-year study. The modeling showed that S. Kentucky in this herd was of mild infectiousness and had a long infectious period, which together provide an explanation for the observed prevalence pattern after invasion. The prevalence of animals shedding S. Kentucky gradually increased during the epidemic phase after which a relatively stable long-term endemic infection was established in the herd. In addition, the data indicate that the time since infection is important in the transmission dynamics of S. Kentucky in adult dairy cattle. New data on the dynamics of S. Kentucky infection in a dairy herd may lead to improved methods for control of commensal Salmonella infections in dairy herds. This information will be useful to other scientists and to regulatory agencies.

Technical Abstract: An outbreak of Salmonella Kentucky followed by a high level of sustained endemic prevalence was recently observed in a US adult dairy herd enrolled in a longitudinal study involving intensive fecal sampling. To understand the invasion ability and transmission dynamics of Salmonella Kentucky in dairy cattle, accurate estimation of the key epidemiological parameters from longitudinal field data is necessary. The approximate Bayesian computation technique was applied for estimating the transmission rate (ß), the recovery rate (') and shape (n) parameters of the gamma distribution for the infectious (shedding) period, and the basic reproduction ratio (R0), given a susceptible-infectious-recovered-susceptible (SIRS) compartment model with a gamma distribution for the infectious period. The results report that the mean transmission rate (ß) is 0.417 month-1 (median: 0.417, 95% credible interval [0.406, 0.429]), the average infectious period ('-1) is 7.95 months (median: 7.95, 95% credible interval [7.70, 8.22]), the mean shape parameter (n) of the gamma distribution for the infectious period is 242 (median: 182, 95% credible interval [16, 482]), and the mean basic reproduction ratio (R0) is 2.91 (median: 2.91, 95% credible interval [2.83, 3.00]). This study shows that Salmonella Kentucky in this herd was of mild infectiousness and had a long infectious period, which together provide an explanation for the observed prevalence pattern after invasion. The transmission rate and the recovery rate parameters are inferred with better accuracy than the shape parameter, therefore these two parameters are more sensitive to the model and the observed data. The estimated shape parameter (n) has large variability with a minimal value greater than one, indicating that the infectious period of Salmonella Kentucky in dairy cattle does not follow the conventionally assumed exponential distribution.