Why Pandemics Are Returning and How We Can Prevent Future Pandemics

Pandemics - infectious diseases that spread worldwide - appear to be returning with increasing frequency.

The Middle Ages saw the Black Death, or plague, while the period after the First World War brought the Spanish flu. These illnesses claimed tens of millions of lives.

Science subsequently began to gain the advantage. Vaccination eliminated smallpox and has come close to doing the same for polio. Antibiotics provided treatment for bacterial infections, followed more recently by antiviral medicines.

Yet pandemics have appeared to resurge over recent decades. HIV/AIDS emerged in the 1980s, followed by several influenza pandemics, SARS and now COVID (no, COVID isn't over).

Why is this occurring, and can future pandemics be prevented?

Unbalanced ecosystems

Thriving, stable ecosystems deliver services that support human health. They provide food and clean water, generate oxygen, and offer green spaces that benefit recreation and wellbeing.

Disease regulation is another essential function of ecosystems. When nature remains balanced - with predators limiting herbivore numbers and herbivores regulating plant growth - pathogens are less likely to emerge in ways that lead to pandemics.

However, human disruption of ecosystems, including through climate change and biodiversity loss, can upset this balance.

Climate change, for instance, alters the abundance and geographical distribution of plants and animals. As the planet warms, disease-carrying mosquitoes can expand from tropical regions into areas that were once temperate, potentially exposing more people during months that would normally be free of disease.

We have examined the link between weather conditions and dengue fever transmission in China. Our results reinforce the conclusion of many other studies: climate change is likely to place more people at risk of dengue.

Biodiversity loss can produce comparable consequences by disturbing food chains. During the first half of the 20th century, ranchers in South America cleared forests to make grazing land for cattle. Small, forest-dwelling vampire bats that feed on blood suddenly had a smörgåsbord of large, stationary animals available to them.

Previously, the limited food supply and the presence of predators within the balanced forest ecosystem had constrained vampire bat populations. In South America, however, the numbers of these bats increased dramatically.

Vampire bats carry the rabies virus, which can cause fatal brain infections in people they bite. Vaccination programmes in South America have greatly reduced deaths from bat-borne rabies, but rabies transmitted through bites from other animals remains a worldwide threat.

As urban and agricultural expansion encroaches on natural ecosystems, humans and domestic animals have more opportunities to acquire pathogens usually found only in wildlife. This is especially the case where people hunt and eat wild animals.

For example, the HIV virus first entered human populations through apes killed for food in Africa, before spreading around the world through travel and trade.

Bats, meanwhile, are believed to have been the original reservoir for the virus responsible for the COVID pandemic, which has killed more than 7 million people to date.

Unless we effectively deal with the unsustainable effects we are having on the planet, pandemics will continue to arise.

Targeting the ultimate causes

Climate change, biodiversity loss and other global challenges are the ultimate, or high-level, causes of pandemics. Greater contact between people, domestic animals and wildlife, by contrast, is the proximate, or immediate, cause.

With HIV, direct exposure to infected ape blood was the proximate cause. But the apes were being killed because many people living in severe poverty were hungry - an ultimate cause.

This difference between ultimate and proximate causes matters because responses often focus solely on proximate causes. People may smoke because of stress or social pressure, which are ultimate causes of developing lung cancer, while the toxins in cigarette smoke cause cancer directly, making them the proximate cause.

In general, health services concentrate on helping people stop smoking and treating the resulting disease, rather than removing the underlying factors that encouraged them to smoke initially.

Pandemics are handled similarly: lockdowns, mask wearing, social distancing and vaccination all aim to halt viral transmission. Far less attention has been given to tackling the ultimate causes of pandemics - perhaps until very recently.

A planetary health approach

Awareness is growing of the need to adopt a "planetary health" approach to improving human health. The concept recognises that human health and civilisation rely on healthy natural systems and the responsible stewardship of those systems.

Under this approach, preventing future pandemics would prioritise ultimate drivers such as climate change and biodiversity loss. At the same time, experts from a wide range of disciplines would work together to address proximate causes, reducing overall risk.

A planetary health approach can improve environmental health and human health at the same time. We are encouraged by the growing inclusion of planetary health concepts in environmental science, humanities and health science teaching at many universities.

As climate change, biodiversity loss, population displacement, travel and trade continue to raise the likelihood of disease outbreaks, future stewards of the planet must gain a stronger understanding of how to confront the ultimate causes driving pandemics.

Olga Anikeeva, Research Fellow, School of Public Health, University of Adelaide; Jessica Stanhope, Lecturer, School of Allied Health Science and Practice, University of Adelaide; Peng Bi, Professor, School of Public Health, University of Adelaide; and Philip Weinstein, Professorial Research Fellow, School of Public Health, University of Adelaide

This article is republished from The Conversation under a Creative Commons licence. Read the original article.