Biomedical subjects

Christopher A Gilligan

Publications and source records attributed to Christopher A Gilligan.

4 recordsLinked to original sources

PubMed2006

Evaluating the performance of chemical control in the presence of resistant pathogens.

Resistance to chemical control is a major impediment to combating many socially and economically important diseases. Theoretical and experimental studies have shown that reducing the intensity of treatment can slow, or even prevent, the invasion of resistance, yet reducing treatment levels also results in a net increase in disease severity. Clearly there is a need to identify control strategies that balance the conflicting aims of resistance management and disease suppression. Using a mathematical model for the dynamics of fungicide resistance in crop pathogens, we present a broadly applicable measure of the performance of chemical control in the presence of resistant pathogen strains. We illustrate how to optimise fungicide performance with respect to the intensity of treatment as a function of the duration of treatment and the fitness of the resistant strain. We find that in the short term, fungicide performance is optimised at high levels of treatment despite rapid selection for resistance, while the long-term optimum performance is achieved when treatment renders the fungicide-sensitive and fungicide-resistant pathogens equally fit. We further present evidence that under prescribed conditions, the ratio of dose size and frequency, and the fungicide mode of action, can have a significant effect on fungicide performance.

Drug Resistance, Fungal↗

PubMed2006

Transient population dynamics in periodic matrix models: methodology and effects of cyclic permutations.

Many biological populations are subject to periodically changing environments such as years with or without fire, or rotation of crop types. The dynamics and management options for such populations are frequently investigated using periodic matrix models. However the analysis is usually limited to long-term results (asymptotic population growth rate and its sensitivity to perturbations of vital rates). In non-periodic matrix models it has been shown that long-term results may be misleading as populations are rarely in their stable structure. We therefore develop methods to analyze transient dynamics of periodic matrix models. In particular, we show how to calculate the effects of perturbations on population size within and at the end of environmental cycles. Using a model of a weed population subject to a crop rotation, we show that different cyclic permutations produce different patterns of sensitivity of population size and different population sizes. By examining how the starting environment interacts with the initial conditions, we explain how different patterns arise. Such understanding is critical to developing effective management and monitoring strategies for populations subject to periodically recurring environments.

Daucus carota↗

PubMed2004

Using conservation of pattern to estimate spatial parameters from a single snapshot.

Rapid reaction in the face of an epidemic is a key element in effective and efficient control; this is especially important when the disease has severe public health or economic consequences. Determining an appropriate level of response requires rapid estimation of the rate of spread of infection from limited disease distribution data. Generally, the techniques used to estimate such spatial parameters require detailed spatial data at multiple time points; such data are often time-consuming and expensive to collect. Here we present an alternative approach that is computationally efficient and only requires spatial data from a single time point, hence saving valuable time at the start of the epidemic. By assuming that fundamental spatial statistics are near equilibrium, parameters can be estimated by minimizing the expected rate of change of these statistics, hence conserving the general spatial pattern. Although applicable to both ecological and epidemiological data, here we focus on disease data from computer simulations and real epidemics to show that this method produces reliable results that could be used in practical situations.

Animals↗

PubMed2004

Invasion of drug and pesticide resistance is determined by a trade-off between treatment efficacy and relative fitness.

Drug and pesticide resistance are among the most pressing problems facing public, animal and plant health today. In order to design effective resistance management strategies it is imperative to identify criteria for the invasion of resistant forms. Two key determinants of the ability of a resistant pest or pathogen to invade are any inherent fitness costs to the resistant subpopulation, and the effect of treatment on the sensitive and resistant subpopulations. For two generic classes of model which encompass many of the standard models in this field, we summarize relative fitness and treatment efficacy via two simple parameters, and demonstrate that invasion of resistance depends critically on a trade-off between them. Thresholds for invasion are derived when the effect of treatment is a constant reduction in the life-history parameters of the pathogen, and when treatment efficacy varies periodically with the repeated application and subsequent decay of the chemical.

Adaptation, Biological↗