Disease Ecology

Abstract

The role of infectious disease in human history is well known, but its importance in ecology has been neglected until relatively recently. Disease ecology involves using ecological principles and concepts to understand and manage infectious diseases, in humans, other animals and plants. It is strongly based on mathematical theory and modelling approaches. The most important concept is R 0 , the number of secondary cases per primary case when disease is rare. If it is greater than one, infection will increase in the population, but if it can be driven below one, disease can be eliminated. Most infectious agents affect more than one host species, and most host species harbour several species of parasite. Understanding the community context of infectious disease is, therefore, essential. Human‐induced changes, such as habitat destruction and fragmentation and climate change, can be expected to have major effects on the impact of infectious disease in natural ecosystems. Key Concepts Parasites and pathogens are important factors in understanding the evolution and ecology of organisms, but their importance is often not recognised. The basic reproductive number R 0 (the number of secondary cases per primary case when disease is rare) is the single most important concept in understanding the ecology of disease. If R 0 > 1, the disease can increase in the host population, but if R 0 < 1, disease cannot establish. Microparasites, such as viruses, bacteria, and protozoans, can often be modelled by dividing the host population into susceptible, infected and resistant classes. For macroparasites such as worms, however, it is essential to consider the level of infection and recognise that a few hosts usually harbour most of the total parasite population. Most parasite species infect more than one host species, and most hosts harbour several parasite species. It is essential to consider interactions between parasites within hosts and the effect of differing susceptibility of multiple host taxa. Environmental changes produced by humans, such as climate change and habitat destruction, have major impacts on parasites and their effect on host populations.