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The Interface Between Epidemiology and Population Genetics

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Abstract

Modern biology increasingly integrates disparate disciplines. Here, Steve Paterson and Mark Viney examine the interface between epidemiology and population genetics. They argue that infection and inheritance can be considered as analogous processes, and that epidemiology and population genetics share many common features. They consider the potential for existing population genetic theory to dissect epidemiological patterns in field studies and they consider other relationships between genetics and epidemiology that provide a research challenge for the future.

Section snippets

The interface of inheritance and infection

Modeling drug resistance in parasite populations is one area where population genetics and epidemiology come together 4., 5.. The task is to construct a model that combines both the spread of drug-resistance genes through a parasite population and the spread of drug-resistant parasites through a host population (Box 1). Recent work by Smith et al. 6 provides a good example of how this can be achieved. Here, the basic unit of the model is the parasite itself, rather than the infected host.

Transmission and gene flow

Parasite transmission at the individual scale describes the infection of one host by another. Although this is the scale at which it is often considered, this process also extends to the population level and, at the largest scale, can describe the spread of a parasite species, strain or genotype across a continent. The concept of gene flow in population genetics describes the movement of genes through or between populations 2. In this respect, it is analogous to parasite transmission at the

Transmission heterogeneity

Many of the theoretical challenges faced by epidemiologists and population geneticists are problems of scale. How does one go from a mechanistic explanation of an underlying process at the individual level to the population-level consequences of that process? A particular challenge common to both epidemiology and population genetics is the introduction of heterogeneity into the underlying process — infection or inheritance — and its consequence upon population-level dynamics 3.

The use of

Emergent properties and epistasis

Spatial modeling in epidemiology has highlighted the importance of interactions between individuals for infection dynamics. Interactions between genes might play just as an important role in population genetics. Genetically complex traits such as weight, height, etc. are governed not by a single locus, but by a large number of loci. How do these loci act to produce a complex trait? In the simplest case, the effect of each locus is additive (Fig. 1a) — the sum of the effects of all the loci

Infection and disease

Epidemiology studies the population dynamics of disease; however, infection per se is not equivalent to disease. Infection is the presence of infectious agents in a host, disease is the deviation from normal health. Thus, disease is a possible, but not a necessary, outcome of infection. Consider hookworm infection. To understand hookworm disease, it is not enough to know whether a patient is infected. Rather, one also needs to know how many hookworms are present within a patient. An infection

Working at the interface

What benefits will result from work at the interface of population genetics and epidemiology? First, population genetic and epidemiological models are now becoming integrated, especially in models of anthelmintic resistance. This is a trend to be welcomed because it helps to produce predictive models for use in parasite control programmes. Second, field studies using molecular markers and population genetic theory should encourage the development of epidemiological models that provide a deeper

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