Infectious disease emergence and global change: thinking systemically in a shrinking world

Abstract

Background: Concern intensifying that emerging infectious diseases and global environmental changes that could generate major future human pandemics.

Method: A focused literature review was undertaken, partly informed by a forthcoming report on environment, agriculture and infectious diseases of poverty, facilitated by the Special Programme for Tropical Diseases.

Results: More than ten categories of infectious disease emergence exist, but none formally analyse past, current or future burden of disease. Other evidence suggests that the dominant public health concern focuses on two informal groupings. Most important is the perceived threat of newly recognised infections, especially viruses that arise or are newly discovered in developing countries that originate in species exotic to developed countries, such as non-human primates, bats and rodents. These pathogens may be transmitted by insects or bats, or via direct human contact with bushmeat. The second group is new strains of influenza arising from intensively farmed chickens or pigs, or emerging from Asian "wet markets" where several bird species have close contact. Both forms appear justified because of two great pandemics: HIV/AIDS (which appears to have originated from bushmeat hunting in Africa before emerging globally) and Spanish influenza, which killed up to 2.5% of the human population around the end of World War I. Insufficiently appreciated is the contribution of the milieu which appeared to facilitate the high disease burden in these pandemics. Additionally, excess anxiety over emerging infectious diseases diverts attention from issues of greater public health importance, especially: (i) existing (including neglected) infectious diseases and (ii) the changing milieu that is eroding the determinants of immunity and public health, caused by adverse global environmental changes, including climate change and other components of stressed life and civilisation-supporting systems.

Conclusions: The focus on novel pathogens and minor forms of anti-microbial resistance in emerging disease literature is unjustified by their burden of disease, actual and potential, and diverts attention from far more important health problems and determinants. There is insufficient understanding of systemic factors that promote pandemics. Adverse global change could generate circumstances conducive to future pandemics with a high burden of disease, arising via anti-microbial and insecticidal resistance, under-nutrition, conflict, and public health breakdown.

Figure 1

Outline of the results section of this paper. The paper presents three linked conceptual frameworks, leading to the overall conclusion. Several datasets are used.

Figure 2

FAO food index 1990-August 2012, Global food crises have increased substantially since 2005. The second rise, after 2010, has probably resulted more from extreme weather events than from high energy prices, or from biofuels (raw data, FAO).

Figure 3

Fourteen categories of EID events described by Jones et al. [[7]].

Figure 4

Two perspective on EIDs and Global Change. The dominant perspective in the EID literature is currently to look to the left of the black line in this figure, discounting the existing health consequences of infectious diseases of poverty and the future risks to EIDs due to adverse global change. In contrast this paper focuses mainly on the view to the right side of this line. However, it also argues that the public health risks of EIDs, as mostly perceived, are exaggerated.

Figure 5

Highly pathogenic avian influenza is more likely to evolve in the pathogenic milieu in the chicken Concentrated Animal Feeding Operation (CAFO) (right) than the wild bird flock (left), where low pathogenic forms are more likely (adapted from [[99]].

Figure 6

From 1960 to about 1980 per capita production of the top 20 food crops (by tonnage) rose steeply, associated with a dramatic fall in global hunger (including as a proportion). In the last few years per capita production of these crops has again risen, yet global hunger has worsened. Raw data FAO (FAOSTAT), UN Population Division.

Figure 7

This figure shows the same data as in Figure6, excluding sugar and maize, which increasingly have been used for ethanol rather than food. The trend in per capita agricultural production is much flatter since about 1980, however the increase from 1961 to about 1980 is similar in both figures. Raw data FAO (FAOSTAT), UN population division.

Figure 8

Pathways between adverse global change and catastrophic emerging diseases. This figure show a subset of these pathways, considered by the author to be of the greatest importance.

Figure 9

Pathways towards a more encouraging future. With new thinking, better leadership, less waste and new technologies, especially to produce clean and abundant energy food prices could stabilize, the rate of climate change would slow and nutrition would improve. In this milieu, progress would continue to be made to deal with existing infectious diseases of poverty, and the risk of emerging diseases with a catastrophic burden of disease would abate. The main global health problems would be of chronic diseases and diseases of ageing.