Emerging human infectious diseases and the links to global food production

Abstract

Infectious diseases are emerging globally at an unprecedented rate while global food demand is projected to increase sharply by 2100. Here, we synthesize the pathways by which projected agricultural expansion and intensification will influence human infectious diseases and how human infectious diseases might likewise affect food production and distribution. Feeding 11 billion people will require substantial increases in crop and animal production that will expand agricultural use of antibiotics, water, pesticides and fertilizer, and contact rates between humans and both wild and domestic animals, all with consequences for the emergence and spread of infectious agents. Indeed, our synthesis of the literature suggests that, since 1940, agricultural drivers were associated with >25% of all - and >50% of zoonotic - infectious diseases that emerged in humans, proportions that will likely increase as agriculture expands and intensifies. We identify agricultural and disease management and policy actions, and additional research, needed to address the public health challenge posed by feeding 11 billion people.

Keywords: Agriculture; Developing world; Diseases; Ecological epidemiology; Risk factors.

Fig. 1. Some common relationships between agriculture and human health.

Agricultural production can improve human health by reducing food prices and enhancing nutrition, which can increase resistance to infectious diseases. However, freshwater habitats established for irrigation, as well as other agricultural inputs, often increase the risk of vector-borne diseases, such as malaria and schistosomiasis. In general, rural residents are most vulnerable to these increases in infectious disease, whereas consumers some distance away derive most of the benefits from increased food production. To maximize human health given the impending 11 billion humans projected on the planet by 2100, society must minimize the adverse consequences of agricultural growth while maximizing the health benefits. Images by Kate Marx.

Fig. 2. Proposed effects of human population growth and associated increases in agricultural production on the risk of human infectious diseases.

The black arrows represent the direction of hypothesized mean responses, up (down) indicating increased (decreased) risk. Schistosoma worm image reproduced from ref. under a Creative Commons licence CC BY 4.0. Ebola virus image credit: CDC/Dr Frederick A. Murphy.

Fig. 3. Projected increase in global human population and its expected effect on components of agriculture.

a–f, Past and projected increases in global human population (a), nitrogen (b), phosphorous (c), fertilizer and pesticide use (d), cropland area (e), and irrigated land area (f) and associated 95% prediction bands (light blue bands). ‘Nitrogen’ refers to the normalized estimated global amount of nitrogen nutrients in fertilizers produced (originally reported in thousands of tonnes, now in metric tonnes). ‘Phosphorous’ refers to the normalized estimated global amount of P₂O₅ nutrients in fertilizers produced (originally reported in thousands of tonnes, now in metric tonnes). For a, data were collected from the World Bank. For b–f, data were collected from the Food and Agriculture Organization of the United Nations and statistical models were developed based on the relationships between these variables and global human population density. After the best model was identified, year was substituted for human population density based on the fit in a. These projections should be evaluated with considerable caution because the models assume that human population size is the only factor that affects fertilizer and pesticide use and the amount of arable and irrigated cropland, when in reality, many factors affect these responses (for example, climate, diets, type of crops grown and so on). They merely illustrate that even an extremely parsimonious model seems to track past patterns tolerably well and thus could serve as a basis for coarse projections. See Supplementary Methods for details of the statistical models used to generate these figures and Supplementary Table 1 for coefficients and statistics for the best-fitting models.

Fig. 4. Livestock pathogens and zoonoses.

Percentage of livestock pathogens that infect multiple host species, human pathogens that are currently or originally zoonotic^,, and recent emerging pathogens that are zoonotic^,.

Fig. 5. Effects of agricultural drivers on emerging infectious diseases (EIDs) and zoonotic EIDs of humans since 1940.

a,b, Agricultural drivers were associated with 25% of all (a) and nearly 50% of zoonotic (b) diseases that emerged in humans. For these figures, we use the definition of a zoonotic EID provided by Jones et al., which is a disease that emerged via non-human to human transmission, not including vectors. See Supplementary Methods for the methods used to develop this figure.