Periodicity in host availability does not account for evolutionary branching as observed in many plant pathogens: an application to Gaeumannomyces graminis var. tritici.

Periodicity in host availability is common in agricultural systems. Although it is known to have profound effects on plant pathogen abundance, the evolutionary consequences of periodicity for the pathogen population have not previously been analyzed. An epidemiological model incorporating periodic absence of the host crop is combined with the theory of adaptive dynamics to determine whether or not seasonality in host presence plays a role in the occurrence of evolutionary branching, leading to coexisting yet genetically distinct pathogen phenotypes.

Balancing detection and eradication for control of epidemics: sudden oak death in mixed-species stands.

Culling of infected individuals is a widely used measure for the control of several plant and animal pathogens but culling first requires detection of often cryptically-infected hosts. In this paper, we address the problem of how to allocate resources between detection and culling when the budget for disease management is limited. The results are generic but we motivate the problem for the control of a botanical epidemic in a natural ecosystem: sudden oak death in mixed evergreen forests in coastal California, in which species composition is generally dominated by a spreader species (bay laurel) and a second host species (coast live oak) that is an epidemiological dead-end in that it does not transmit infection but which is frequently a target for preservation.

Epidemics in networks of spatially correlated three-dimensional root-branching structures.

Using digitized images of the three-dimensional, branching structures for root systems of bean seedlings, together with analytical and numerical methods that map a common susceptible-infected-recovered ('SIR') epidemiological model onto the bond percolation problem, we show how the spatially correlated branching structures of plant roots affect transmission efficiencies, and hence the invasion criterion, for a soil-borne pathogen as it spreads through ensembles of morphologically complex hosts. We conclude that the inherent heterogeneities in transmissibilities arising from correlations in the degrees of overlap between neighbouring plants render a population of root systems less susceptible to epidemic invasion than a corresponding homogeneous system. Several components of morphological complexity are analysed that contribute to disorder and heterogeneities in the transmissibility of infection.

Heterogeneity in susceptible-infected-removed (SIR) epidemics on lattices.

The percolation paradigm is widely used in spatially explicit epidemic models where disease spreads between neighbouring hosts. It has been successful in identifying epidemic thresholds for invasion, separating non-invasive regimes, where the disease never invades the system, from invasive regimes where the probability of invasion is positive. However, its power is mainly limited to homogeneous systems.

Appropriate research designs for evaluating community-level alcohol interventions: what next?

Aim: The aim of this study was to explore the logistical and methodological strengths and weaknesses of some of the more common research designs which can be used to evaluate the impact of system- or population-level approaches for reducing alcohol-related harms.

Method: This paper identifies studies that have evaluated system or population approaches to reduce alcohol-related harms. It highlights the tension caused by a desire for the most rigorous research designs, such as randomized controlled trials (RCTs), the most potentially efficacious interventions and the practical problems in applying the RCT to population-level research.

The effect of landscape pattern on the optimal eradication zone of an invading epidemic.

A number of high profile eradication attempts on plant pathogens have recently been attempted in response to the increasing number of introductions of economically significant nonnative pathogen species. Eradication programs involve the removal of a large proportion of a host population and can thus lead to significant social and economic costs. In this paper we use a spatially explicit stochastic model to simulate an invading pathogen and show that it is possible to identify an optimal control radius, i.

Economically optimal timing for crop disease control under uncertainty: an options approach.

Severe large-scale disease and pest infestations in agricultural regions can cause significant economic damage. Understanding if and when disease control measures should be taken in the presence of risk and uncertainty is a key issue. We develop a framework to examine the economically optimal timing of treatment.

Assessing the accuracy of self-reported smoking status and impact of passive smoke exposure among pregnant Aboriginal and Torres Strait Islander women using cotinine biochemical validation.

Introduction And Aims: A significant level of misreport or error occurs during questionnaire-based assessment of smoking behaviour. Failure to measure environmental tobacco smoke, and participant's inclination to under-report their smoking raise questions as to the accuracy of assessment. In order to establish an estimation of the possible error associated with such assessment, the accuracy of self-reported smoking status among a group of pregnant Aboriginal and Torres Strait Islander women was examined.

Complexity and anisotropy in host morphology make populations less susceptible to epidemic outbreaks.

One of the challenges in epidemiology is to account for the complex morphological structure of hosts such as plant roots, crop fields, farms, cells, animal habitats and social networks, when the transmission of infection occurs between contiguous hosts. Morphological complexity brings an inherent heterogeneity in populations and affects the dynamics of pathogen spread in such systems. We have analysed the influence of realistically complex host morphology on the threshold for invasion and epidemic outbreak in an SIR (susceptible-infected-recovered) epidemiological model.

Development of a neutron-activated concrete powder reference material.

In this paper, the development of a neutron-activated concrete powder reference material is described. The material originated from core samples taken from a concrete bioshield of a decommissioned nuclear reactor which ceased operation almost 30 years ago after approximately 20 years of operation. The assigned values, which were in the Bq g(-1) range, for the radionuclides in the material were determined by a 'consensus' method from measurements made by 33 organisations from 15 countries.

Tobacco use and measuring nicotine dependence among urban Indigenous pregnant women.

Objectives: To examine patterns of nicotine dependence, the value of the Fagerström Test for Nicotine Dependence (FTND) and its correlation with self-reported tobacco use and urinary cotinine concentrations among pregnant Indigenous women in Townsville.

Design, Participants And Setting: Cross-sectional study of 201 consecutive women who self-reported tobacco use at their first antenatal visit to Townsville Aboriginal and Islander Health Service (TAIHS) between 1 November 2005 and 31 October 2007. All smokers were to be assessed by FTND, and 108 women participating in the Tilly's Tracks project (a randomised trial of an intervention to reduce smoking in pregnant Aboriginal and Torres Strait Islander women) were to have a comprehensive smoking history taken and urinary cotinine samples collected.

Optimization of control strategies for epidemics in heterogeneous populations with symmetric and asymmetric transmission.

There is growing interest in incorporating economic factors into epidemiological models in order to identify optimal strategies for disease control when resources are limited. In this paper we consider how to optimize the control of a pathogen that is capable of infecting multiple hosts with different rates of transmission within and between species. Our objective is to find control strategies that maximize the discounted number of healthy individuals.

Optimal strategies for the eradication of asiatic citrus canker in heterogeneous host landscapes.

ABSTRACT The eradication of nonnative plant pathogens is a key challenge in plant disease epidemiology. Asiatic citrus canker is an economically significant disease of citrus caused by the bacterial plant pathogen Xanthomonas citri subsp. citri.

Invasion, persistence and control in epidemic models for plant pathogens: the effect of host demography.

Many epidemiological models for plant disease include host demography to describe changes in the availability of susceptible tissue for infection. We compare the effects of using two commonly used formulations for host growth, one linear and the other nonlinear, upon the outcomes for invasion, persistence and control of pathogens in a widely used, generic model for botanical epidemics. The criterion for invasion, reflected in the basic reproductive number, R(0), is unaffected by host demography: R(0) is simply a function of epidemiological parameters alone.

Epidemiological analysis of take-all decline in winter wheat.

Take-all dynamics within crops differing in cropping history (the number of previous consecutive wheat crops) were analyzed using an epidemiological model to determine the processes affected during take-all decline. The model includes terms for primary infection, secondary infection, inoculum decay, and root growth. The average rates of root production did not vary with cropping history.

Knowledge and attitudes regarding smoking during pregnancy among Aboriginal and Torres Strait Islander women.

Objective: To identify factors associated with antenatal smoking and explore characteristics of smoking behaviour among pregnant Aboriginal and Torres Strait Islander women.

Design And Setting: Cross-sectional study using interviewer-administered questionnaires of 145 pregnant Aboriginal and Torres Strait Islander women attending a health service in Far North Queensland between November 2005 and December 2006.

Main Outcome Measures: Prevalence of self-reported smoking; predictors and patterns of smoking in early pregnancy; and relationships between smoking and the prevalence of predisposing, enabling and reinforcing factors, including women's knowledge about and attitudes towards smoking and the risks involved.

Identifying pregnant women at risk of poor birth outcomes.

Pregnancy is a vulnerable period in women's lives, with a range of maternal and environmental factors impacting upon pregnancy outcome. This study sought to explore the clustering of health risks among pregnant women, and compare the characteristics of women exhibiting clustered risks. A cross-sectional study was undertaken at a large public hospital in Queensland, Australia.

Optimal control of epidemics in metapopulations.

Little is known about how best to deploy scarce resources for disease control when epidemics occur in different but interconnected regions. We use a combination of optimal control methods and epidemiological theory for metapopulations to address this problem. We consider what strategy should be used if the objective is to minimize the discounted number of infected individuals during the course of an epidemic.

Modelling control of epidemics spreading by long-range interactions.

We have studied the spread of epidemics characterized by a mixture of local and non-local interactions. The infection spreads on a two-dimensional lattice with the fixed nearest neighbour connections. In addition, long-range dynamical links are formed by moving agents (vectors).

Dynamics of primary and secondary infection in take-all epidemics.

ABSTRACT Using a combination of experimentation and mathematical modeling, the effects of initial (particulate) inoculum density on the dynamics of disease resulting from primary and secondary infection of wheat by the take-all fungus, Gaeumannomyces graminis var. tritici, were tested. A relatively high inoculum density generated a disease progress curve that rose monotonically toward an asymptote.

Large-scale fungicide spray heterogeneity and the regional spread of resistant pathogen strains.

ABSTRACT Most models for the spread of fungicide resistance in plant pathogens are focused on within-field dynamics, yet regional invasion depends upon the interactions between field populations. Here, we use a spatially implicit metapopulation model to describe the dynamics of regional spread, in which subpopulations correspond to single fields. We show that the criterion for the regional invasion of pathogens between fields differs from that for invasion within fields.

An Epidemiological Analysis of the Role of Disease-Induced Root Growth in the Differential Response of Two Cultivars of Winter Wheat to Infection by Gaeumannomyces graminis var. tritici.

ABSTRACT Epidemiological modeling combined with parameter estimation of experimental data was used to examine differences in the contribution of disease-induced root production to the spread of take-all on plants of two representative yet contrasting cultivars of winter wheat, Ghengis and Savannah. A mechanistic model, including terms for primary infection, secondary infection, inoculum decay, and intrinsic and disease-induced root growth, was fitted to data describing changes in the numbers of infected and susceptible roots over time at a low or high density of inoculum. Disease progress curves were characterized by consecutive phases of primary and secondary infection.

Epidemiology and chemical control of take-all on seminal and adventitious roots of wheat.

ABSTRACT Epidemiological modeling is used to examine the effect of silthiofam seed treatment on field epidemics of take-all in winter wheat. A simple compartmental model, including terms for primary infection, secondary infection, root production, and decay of inoculum, was fitted to data describing change in the number of diseased and susceptible roots per plant over thermal time obtained from replicated field trials. This produced a composite curve describing change in the proportion of diseased roots over time that increased monotonically to an initial plateau and then increased exponentially thereafter.