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Pandemics Have Multiple, Interacting Drivers

Systems thinking is essential to prevent and manage pandemics.

This post was co-authored with Ferenc Jordán and Paul R. Ehrlich.

Wicked problems, like climate disruption, extinction, and pandemics have multiple drivers. The effects of these drivers may be simply additive, where the effect of A and the effect of B sum up to the combined effect C (A+B=C), or be synergistic. Such synergistic effects include interference in a non-additive way, such as seen when there is dampening (A+B>C) or escalation (A+B<C).

To manage wicked problems we must think systematically about these potential relationships. Just like the major threats to nature are caused by multiple drivers of change (1), the current threats to human health are generated by multiple, interacting drivers (2). We need to view the complexity of socio-ecological challenges from a systems perspective more than ever.

The current coronavirus pandemic is a textbook example of synergistic effects and warns us that this is not a 1 in 100-year pandemic but rather that it is an expected consequence of our 21st-century global lifestyle. We know that population growth and urbanization result in increased epidemic risk (3), by creating high population density hot spots for diseases. Combined with poverty, population growth also increases zoonotic risk, because more people eat wild animals, including those purchased at "wet markets" (4). In combination with globalized transportation networks, population growth increases epidemic risk by dramatically speeding up and extending the range of the spread of human-transmitted diseases (5).

The loss of natural habitats, combined with urbanization, has a positive force-multiplying effect of increasing the nature and magnitude of human-animal contacts, which further increases zoonotic risks (6). This latter process is accelerated by climate change (7), which drives a number of mobile species, including disease vectors, to expand their ranges. The effects of climate change can be further exacerbated by habitat fragmentation, increasing human-animal contact: The mobility of predators is often limited, so they cannot respond to environmental changes and stay closer to human settlements (8).

These interconnected drivers suggest that while simple interventions may have focused and immediate successes (e.g., physical distancing and wearing masks can reduce R0, and vaccination may protect a vulnerable population), it is essential to think more broadly to avoid future pandemics—whether zoonotic or otherwise.

For this, we need to combine efforts at several scales and in several fields. Managing food supplies and quality may reduce zoonotic spillovers. Humanely reducing the global human population size (by, for example giving women full reproductive rights) and ending overconsumption by the rich would shrink humanity’s ecological footprint. That would reduce exposure to wild animals and disease spillover—with the added benefit of preserving biodiversity. Building resilience into global trade systems will reduce each nation’s vulnerability to supply chain disruptions of food and key medical supplies. Ensuring quality healthcare will help with early detection and treatment. Supporting regional (rather than global) tourism and trade may restrict the spread of epidemics. Finally, reducing habitat fragmentation could help a number of species respond to environmental changes in ways that do not concentrate them in areas of high human density (e.g., white-tailed deer in the Northeastern US) with the resultant zoonotic risks (e.g., Lyme disease) (9).

Yet, even such systems thinking is fraught with trade-offs. For example, while concentrating people into cities may be a viable solution to preserve natural habitats, at the same time it also increases epidemiological risk. Society must choose. Sometimes, by identifying trade-offs, it may be possible to manage them. For instance, compared to large sprawling urban areas, dense, vertical cities are, should the need arise, relatively easy to isolate. And if a key threat is identified, public health efforts can more readily be implemented.

In any case, monitoring and data collection, as well as the analysis and predictive modeling of global diseases are wise strategies (10) and adopting a systems perspective is essential. We must capitalize on lessons learned from nature. These illustrate that there are multiple solutions to many problems. Animals have, after all, evolved camouflage to avoid predators, armor to defend themselves against attack, and the ability to rapidly flee predators. But these are often different solutions (a given species does not typically have all traits) illustrating that there may be multiple adaptive peaks. By having a given solution, it’s possible to not easily shift to another one (heavily armored species are not likely to evolve rapid flight).

Additionally, nature is replete with both redundancy and modularization (11). A diversity of potential strategies is already seen in different countries’ policies; some may be especially effective in the context of that country, while others may have more general applicability and can be scaled up. Regardless, we should anticipate different solutions in different socio-cultural contexts; the best solution in India may not be the best in Switzerland, and vice-versa. Isolation, social distancing, developing herd-immunity, and mass testing all might be priorities depending on specific constraints which include demographic (e.g., a country’s age structure), financial (wealthier countries may have more options), and logistical (government-run health systems may facilitate testing, treatment, and vaccination more easily than a free-market health system). Redundancy is seen when laboratories throughout the world work to develop tests and vaccines. We must recognize that modularity is a tool for control; global and group-level social networks can be automatically modularized to respond to a pandemic (12). If they are not, reducing travel will increase their modularization. Taking a systems perspective means that we must examine the interconnections among multiple factors

We must learn from our successes and failures in how we respond to our current pandemic to actively reduce the risk of the next global disease. To do so, we should recognize that wicked problems can only be solved by systems-based thinking and work to identify specific actions with disproportionate positive effects on reducing pandemic threat. Population size and resource use make disproportionate contributions to increasing pandemic likelihood. It is clear that the biological and social environments are inextricably linked and our actions to make humanity safer from disease epidemics should have the added benefit of preserving the very biodiversity on which our lives depend.

Ferenc Jordán is a professor at the Balaton Limnological Insitute, Tihany, Hungary and at the Stazione Zoologica Anton Dohrn, Napoli, Italy.

Paul R. Ehrlich is a Professor in the Center for Conservation Biology, Stanford University, USA.

References

Please cite this essay as: Jordán, F., Ehrlich, P.R., and D. T. Blumstein. 2020. Pandemics have multiple, interacting drivers.

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8. Michalski, F., Boulhosa, R.L.P., Faria, A., Peres, C.A. 2006. Human–wildlife conflicts in a fragmented Amazonian forest landscape: determinants of large felid depredation on livestock. Animal Conservation 9(2), 179-188.

9. Brownstein, J.S., Skelly, D.K., Holford, T.R., Fish, D. 2005. Forest fragmentation predicts local scale heterogeneity of Lyme disease risk. Oecologia 146, 469–475.

10. Brooks, D. R., Boeger, W. A., Hoberg, E. P. 2019. The Stockholm Paradigm. University of Chicago Press.

11. Sagarin, R., Taylor, T. (Eds.). 2008. Natural Security – a Darwinian Approach to a Dangerous World. University of California Press, Berkeley and Los Angeles, 240-260.

12. Stroeymeyt, N., Grasse, A. V., Crespi, A., Mersch, D. P., Cremer, S., Keller, L. 2018. Social network plasticity decreases disease transmission in an eusocial insect. Science 362, 941–945.

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