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 R0, 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 R0 (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 R0 > 1, the disease can increase in the host population, but if R0 < 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.

Keywords: basic reproductive number; parasites; pathogens; conservation biology; climate change

Figure 1. Compartmental SIR models for infectious diseases. This is a description of a simple model in which transmission is density‐dependent, the pathogen affects only survival (and not fecundity), the pathogen is the only constraint on host population growth and there is no exposed but not yet infectious stage. The model can be modified to relax these assumptions. Hosts are divided into susceptible (S) infected (I) and resistant (R) compartments. Hosts in all compartments have a per capita birth rate a, and a death rate independent of disease b. In infected hosts, the disease increases the death rate by α. Infection occurs in a density‐dependent manner, with a per capita infection rate of susceptible hosts of βI. Infected hosts recover at a rate γ, and resistant hosts lose resistance at a rate ν. (a) The model represented as a flow diagram. (b) An example of an epidemic generated from these equations (a = 0.06, b = 0.04, β = 0.1, ν = 0.02, α = 0.5, γ = 0.5). S and R are scaled on the left axis, and I is scaled on the right axis. The time units are arbitrary.
Figure 2. Counts of frog captures at El Copé, Panama before and after arrival of the amphibian chytrid fungus Batrachochytrium dendrobatidis. Frogs were sampled along four permanent transects, with counts shown as the number of captures per kilometre of stream per person. Counts of diurnal frogs from a number of species were recorded. The fungus was first detected at the site in late September 2004, and reached an overall prevalence of more than 50% by October 2004, with 47 species infected. The line shown is a segmented regression, with the point at which the slope changed estimated from the data as occurring in early September 2004. Source: Data from Lips et al. .
Figure 3. Effect of temperature on malaria transmission. (a) Thermal performance curves for the components of vector biology contributing to R0 (Anopheles spp. mosquitos and Plasmodium falciparum malaria parasites). (b) Overall effect of temperature on R0. The blue line shows the estimate calculated taking into account the nonlinearities shown in (a), in contrast to the previous estimate in red, which was derived using linear relationships between traits and temperatures. The points represent observed data. It is important to note that the calculated R0 represents an upper boundary to the potential malaria transmission: actual transmission rates may be constrained by factors other than temperature, and therefore fall below the theoretical line. Reproduced with permission from Mordecai et al. . © John Wiley and Sons.
close

References

Anderson RM and May RM (1978) Regulation and stability of host–parasite interactions. I. Regulatory processes. Journal of Animal Ecology 47: 219–247.

Anderson RM and May RM (1979) Population biology of infectious diseases. Part I. Nature 280: 361–367.

Anderson RM and May RM (1981) The population dynamics of microparasites and their invertebrate hosts. Philosophical Transactions of the Royal Society B: Biological Sciences 291: 451–524.

Anderson RM and May RM (1982) Coevolution of hosts and parasites. Parasitology 85: 411–426.

Anderson RM and May RM (1991) Infectious Diseases of Humans. Oxford: Oxford University Press.

Antonovics J, Wilson AJ, Forbes MR, et al. (2017) The evolution of transmission mode. Philosophical Transactions of the Royal Society B‐Biological Sciences 372: 12.

Becker MH, Walke JB, Cikanek S, et al. (2015) Composition of symbiotic bacteria predicts survival in Panamanian golden frogs infected with a lethal fungus. Proceedings of the Royal Society B‐Biological Sciences 282.

Bernoulli D (1760) Essai d'une nouvelle analyse de la mortalite, causee par la petite Varole, et des advantages de l'Inoculation pour la prevenir, pp. 1–45. Paris: Memoires de mathematique et de physique, tires des registres de l'Academie Royale des Sciences.

Caminade C, Kovats S, Rocklov J, et al. (2014) Impact of climate change on global malaria distribution. Proceedings of the National Academy of Sciences USA 111: 3286–3291.

Civitello DJ, Cohen J, Fatima H, et al. (2015) Biodiversity inhibits parasites: broad evidence for the dilution effect. Proceedings of the National Academy of Sciences USA 112: 8667–8671.

de Castro F and Bolker B (2005) Mechanisms of disease‐induced extinction. Ecology Letters 8: 117–126.

Dobson AP and Carper ER (1996) Infectious diseases and human population history. Bioscience 46: 115–126.

Faust CL, McCallum HI, Bloomfield LSP, et al. (2018) Pathogen spillover during land conversion. Ecology Letters 21: 471–483.

Foster KR, Schluter J, Coyte KZ and Rakoff‐Nahoum S (2017) The evolution of the host microbiome as an ecosystem on a leash. Nature 548: 43–51.

Grenfell BT and Bolker BM (1998) Cities and villages: infection hierarchies in a measles metapopulation. Ecology Letters 1: 63–70.

Haydon DT, Cleaveland S, Taylor LH and Laurenson MK (2002) Identifying reservoirs of infection: a conceptual and practical challenge. Emerging Infectious Diseases 8: 1468–1473.

Johnson PTJ, Ostfeld RS and Keesing F (2015) Frontiers in research on biodiversity and disease. Ecology Letters 18: 1119–1133.

Krediet CJ, Ritchie KB, Paul VJ and Teplitski M (2013) Coral‐associated micro‐organisms and their roles in promoting coral health and thwarting diseases. Proceedings of the Royal Society B: Biological Sciences 280.

Lafferty KD and Kuris AM (2002) Trophic strategies, animal diversity and body size. Trends in Ecology & Evolution 17: 507–513.

Lips KR, Brem F, Brenes R, et al. (2006) Emerging infectious disease and the loss of biodiversity in a Neotropical amphibian community. Proceedings of the National Academy of Sciences USA 103: 3165–3170.

Lloyd‐Smith JO, George D, Pepin KM, et al. (2009) Epidemic dynamics at the human–animal interface. Science 326: 1362–1367.

Manlove KR, Walker JG, Craft ME, et al. (2016) “One Health” or Three? publication silos among the one health disciplines. PLoS Biology 14: e1002448.

May RM and Anderson RM (1978) Regulation and stability of host–parasite interactions. II. Destabilizing processes. Journal of Animal Ecology 47: 249–267.

May RM and Anderson RM (1979) Population biology of infectious diseases. Part II. Nature 280: 455–461.

May RM and Anderson RM (1990) Parasite–host coevolution. Parasitology 100: S89–S101.

McCallum H (2012) Disease and the dynamics of extinction. Philosophical Transactions of the Royal Society B: Biological Sciences 367: 2828–2839.

McCallum H, Barlow ND and Hone J (2001) How should transmission be modelled? Trends in Ecology and Evolution 16: 295–300.

Mordecai EA, Paaijmans KP, Johnson LR, et al. (2013) Optimal temperature for malaria transmission is dramatically lower than previously predicted. Ecology Letters 16: 22–30.

O'Hanlon SJ, Rieux A, Farrer RA, et al. (2018) Recent Asian origin of chytrid fungi causing global amphibian declines. Science 360: 621.

Pecl GT, Araujo MB, Bell JD, et al. (2017) Biodiversity redistribution under climate change: impacts on ecosystems and human well‐being. Science 355: eaai9214.

Plowright RK, Parrish CR, McCallum H, et al. (2017) Pathways to zoonotic spillover. Nature Reviews Microbiology 15: 502–510.

Randolph SE and Dobson ADM (2012) Pangloss revisited: a critique of the dilution effect and the biodiversity‐buffers‐disease paradigm. Parasitology 139: 847–863.

Scheele BC, Hunter DA, Brannelly LA, Skerratt LF and Driscoll DA (2017) Reservoir‐host amplification of disease impact in an endangered amphibian. Conservation Biology 31: 592–600.

Skerratt LF, Berger L, Speare R, et al. (2007) Spread of chytridiomycosis has caused the rapid global decline and extinction of frogs. EcoHealth 4: 125–134.

Warner RE (1968) The role of introduced diseases in the extinction of the endemic Hawaiian avifauna. Condor 70: 101–120.

Whitmee S et al. (2015) Safeguarding human health in the Anthropocene epoch: report of The Rockefeller Foundation‐Lancet Commission on planetary health. The Lancet 386: 1973–2028.

Further Reading

Aguirre AA, Ostfeld RS and Daszak P (eds) (2012) New Directions in Conservation Medicine: Applied Cases of Ecological Health. New York; Oxford: Oxford University Press.

Keeling MJ and Rohani P (2008) Modeling Infectious Diseases in Humans and Animals. Princeton: Princeton University Press.

Ostfeld RS, Keesing F and Eviner VT (eds) (2008) Infectious Disease Ecology: The Effects of Ecosystems on Disease and of Disease on Ecosystems. Princeton, NJ: Princeton University Press.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
McCallum, Hamish I(Dec 2018) Disease Ecology. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0021215]