Markov chain approach to analyze the dynamics of pathogen fecal shedding - Example of Listeria monocytogenes shedding in a herd of dairy cattle

Department of Food Science, Cornell University, Итак, New York, United States
Journal of Theoretical Biology (Impact Factor: 2.12). 04/2007; 245(1):44-58. DOI: 10.1016/j.jtbi.2006.09.031
Source: PubMed


Fecal shedding is an important mechanism of spreading of a number of human and animal pathogens. Understanding of the dynamics of pathogen fecal shedding is critical to be able to control or prevent the spread of diseases caused by these pathogens. The objective of this study was to develop a model for analysis of the dynamics of pathogen fecal shedding. Fecal shedding of Listeria monocytogenes in dairy cattle was used as a model system. A Markov chain model (MCM) with two states, shedding and non-shedding, has been developed for overall L. monocytogenes fecal shedding (all L. monocytogenes subtypes) and fecal shedding of three L. monocytogenes subtypes (ribotypes 1058A, 1039E and 1042B) using data from one study farm. The matrices of conditional probabilities of transition between shedding and non-shedding states for different sets of covariates have been estimated by application of logistic regression. The covariate-specific matrices of conditional probabilities, describing the presence of different risk factors, were used to estimate (i) the stationary prevalence of dairy cows that shed any L. monocytogenes subtype or ribotypes 1058A, 1039E, and 1042B, (ii) the duration of overall and subtype specific fecal shedding, and (iii) the duration of periods without shedding. A non-homogeneous MCM was constructed to study how the prevalence of fecal shedders changes over time. The model was validated with data from the study farm and published literature. The results of our modeling work indicated that (i) the prevalence of L. monocytogenes fecal shedders varies over time and can be higher than 90%, (ii) L. monocytogenes subtypes exhibit different dynamics of fecal shedding, (iii) the dynamics of L. monocytogenes fecal shedding are highly associated with contamination of silage (fermented feed) and cows' exposure to stress, and (iv) the developed approach can be readily used to study the dynamics of fecal shedding in other pathogen-host-environment systems.

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Available from: Renata Ivanek, Jun 08, 2014
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    • "Moreover, L. monocytogenes can be also shed asymptomatically, persisting in human and animal faeces and be released in the environment [8] [9]. This bacterium also thrives in diverse external environments such as soil, water, decaying plants, and silage, exposing wild animals and cattle to multiple opportunities of ingestion and perpetuating L. monocytogenes transmission [10]. From a food-safety perspective and with the aim of limiting transmission to humans, a lot of emphasis has been focused on reducing bacterial aggregation, biofilm formation and persistence of bacteria on industrial surfaces and food [11]. "
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    ABSTRACT: Listeria monocytogenes is the agent of listeriosis, a food-borne disease. It represents a serious problem for the food industry because of its environmental persistence mainly due to its ability to form biofilm on a variety of surfaces. Microrganisms attached on the surfaces are a potential source of contamination for environment and animals and humans. Titanium dioxide nanoparticles (TiO2 NPs) are used in food industry in a variety of products and it was reported that daily exposure to these nanomaterials is very high. Anti-listerial activity of TiO2 NPs was investigated only with UV-irradiated nanomaterials, based on generation of reactive oxigen species (ROS) with antibacterial effect after UV exposure. Since both Listeria monocytogenes and TiO2 NPs are veicolated with foods, this study explores the interaction between Listeria monocytogenes and non UV-irradiated TiO2 NPs, with special focus on biofilm formation and intestinal cell interaction. Scanning electron microscopy and quantitative measurements of biofilm mass indicate that NPs influence both production and structural architecture of listerial biofilm. Moreover, TiO2 NPs show to interfere with bacterial interaction to intestinal cells. Increased biofilm production due to TiO2 NPs exposure may favour bacterial survival in environment and its transmission to animal and human hosts.
    Full-text · Article · Jan 2014 · PLoS ONE
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    • "However, it is important to bear in mind the challenges in studying transmission of this pathogen related to the overall diversity and variability of L. monocytogenes, even within a single dairy herd, particularly considering the well supported strain variability in L. monocytogenes virulence (Nightingale et al., 2005; Roche et al., 2005). Therefore, the extensive sampling conducted in this study provided particularly valuable data for a better understanding of L. monocytogenes shedding in cattle, and has also formed the basis for a mathematical model on pathogen shedding (Ivanek et al., 2007). "
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    ABSTRACT: Fecal shedding of Listeria monocytogenes poses a risk for contamination of animal feed and agricultural environments and raw food at the pre-harvest stages of food production. To be able to reduce these risks it is critical to improve understanding of the epidemiology of L. monocytogenes shedding in feces. The objective of this study was to assess the daily variability of fecal shedding and its association with individual animal (lactation number and the day of current lactation) and environmental (feed) risk factors. That was achieved by application of longitudinal daily sample collection in a herd of dairy cattle and molecular characterization of isolated L. monocytogenes. Fecal samples (25) and silage samples (2) were collected daily during two 2-week periods and one 5-day period. L. monocytogenes was isolated from 255 out of 825 (31%) fecal samples on 24 out of 33 (73%) days, and from 25 out of 66 (38%) silage samples on 16 out of 33 (48%) days. Ninety-four percent of cows excreted L. monocytogenes in feces at least once during the study period. Our data analyses indicated that (i) the prevalence and incidence risk of L. monocytogenes fecal shedding in cattle vary considerably over time, from 0 to 100%, and both are associated with contamination of silage, (ii) L. monocytogenes fecal shedding in cattle could occur as part of an outbreak or as an isolated sporadic case, (iii) L. monocytogenes subtypes associated with human infections are commonly isolated from cattle feces and silage, and (iv) a single cow can harbor more than one L. monocytogenes subtype on any given day. Although limited to a single dairy cattle herd, these findings provide a significant advancement in the understanding of the epidemiology of L. monocytogenes fecal shedding in dairy cattle.
    Full-text · Article · Sep 2007 · Preventive Veterinary Medicine
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    ABSTRACT: NOTE: An effective introduction to Markov chains and some of their computational science applications can be accomplished by covering the first two parts, "Scientific Questions" and "Computational Models," and omitting the third on "Bioinformatics and Markov Chains." Exercise 1 and Projects 1-5 are accessible with only this background. The third part provides the necessary background for Exercises 2 and 3 and Projects 6-10. The sections entitled "The Area" and "High Performance Computing and Bioinformatics" of that part can be covered on their own as an overview of the need for high performance computing in this important new area of biology and computational science.
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