Preventing Future Pandemics Starts With Recognizing the Tremendous Threats to Global Health From Zoonotic Diseases

Disrupting the habitats of horseshoe bats, such as this one in Borneo, increases the risk of spreading viruses. Credit: Mike Prince/Flickr, CC BY

The COVID-19 pandemic has shown that zoonotic diseases – infections that pass from animals to humans – can pose a huge threat to global health. More than 70% of emerging and re-emerging pathogens come from animals. That likely includes the SARS CoV-2 virus, which scientists widely believe originated in bats.

There are still questions about specifically where the SARS-CoV-2 virus originated. But experts around the world agree that communities can take steps to reduce the risk of future spillovers. It is essential that veterinarians, doctors and scientists work together and recognize how closely human health is linked to that of animals and the habitats we share – an approach known as One Health.

To prevent new pandemics, scientists need to identify specific locations where viruses are most likely to make the leap from animals to humans. This, in turn, requires understanding how human behavior — from deforestation to fossil fuel burning to conflict to cultural activities — contributes to spillover risks.

We focus on global One Health research and education and infectious disease epidemiology, and we were members of a scientific task force convened by the Harvard TH Chan School of Public Health and the Harvard Global Health Institute to update current knowledge on the prevention of of spillovers. The task force’s report noted that a recent analysis estimates the cost of addressing spillovers at risky interfaces through One Health approaches and forest conservation at $22 to 31 billion per year. These costs are dwarfed by the estimated global GDP loss of nearly $4 trillion in 2020 due to the COVID-19 pandemic.

In our view, coordinated investments based on a One Health approach are needed to initiate and support global prevention strategies and avoid the devastating costs of a pandemic.

One Health is a strategy that aims to build bridges between doctors, veterinarians, environmental scientists, public health professionals and other specialists to protect the health of all animal species. Credit: CDC

Recognize risky zones

Identifying areas of high risk for zoonotic spillover is challenging. Humans and wildlife are highly mobile, and exposure may not immediately lead to infection or produce symptoms that clearly indicate exposure to pathogens.

But researchers can make predictions by combining data on people and livestock density with those on environmental conditions, such as deforestation and land use change, which allow pathogens to spread from wildlife to humans. For example, there are areas in China, Indonesia, India and Bangladesh where development has fragmented forests and expanded livestock and human communities near the natural habitats of horseshoe bats. This group of bats, which includes more than 100 species, has been implicated as reservoirs for many coronaviruses.

It is not uncommon for bat-borne diseases to pass to humans. Sometimes it happens instantly: bats in Bangladesh, for example, have repeatedly transmitted the Nipah virus to humans. Or the pathogen can move indirectly via intermediate hosts. In 1994, for example, bats in Australia infected horses with Hendra virus, a respiratory disease that subsequently spread to humans.

In Brazil, yellow fever is endemic to the jungles, mainly spread between monkeys via mosquitoes. People in the country occasionally contract it from mosquito bites, and deforestation and land conversion for agriculture increase the risk of greater spillover effects. There is growing concern that the disease could be introduced into Brazil’s major cities, where Aedes aegypti mosquitoes are widespread and could transmit it on a large scale.

There are also specific human behaviors that can further increase the risk of spillovers. This includes activities where people come into direct contact with or near animals, such as harvesting bat guano (dung) for fertilizer and buying and selling wild animals or animal parts.

Tropical deforestation, wildlife trade and raising livestock near forest edges are considered the main causes of the spread of zoonotic diseases.

Daily routines involving food storage and eating wild animal meat can also pose risks. For example, outbreaks of the Ebola virus in Nigeria have been linked to the slaughter and consumption of bushmeat.

People in high-risk areas for spillovers don’t have to stop living. But they must recognize that some actions are riskier than others and take appropriate safety precautions, such as wearing protective gear and making sure bushmeat is handled and cooked properly.

The importance of teamwork

In our view, it is essential that researchers and governments understand and embrace the central concept that animal, human and environmental health are closely linked and that factors that affect everyone can affect everyone. Ideally, problem-solving teams dealing with prevention should form from the community and district level to the ranks of Ministries of Health, Animals and Environment.

Members of local communities are most likely to know where people are most at risk of coming into contact with animals that can carry infectious diseases. By listening to them, veterinary and medical health professionals, as well as forest rangers and land managers, can develop strategies that are more likely to reduce the risk of overflow.

Camels infected with the Middle East Respiratory Syndrome coronavirus (MERS-CoV) can transmit the virus to humans through direct or indirect contact. Since 2012, MERS has killed more than 800 people in the Middle East, Africa and South Asia. Testing is an important tool for detecting infected animals. Credit: Awadh Mohammed Ba Saleh/CDC Global

Organizations such as the United States Agency for International Development, the Food and Agriculture Organization of the United Nations, national governments and civil society are investing in One Health platforms in selected countries in Africa and Asia. These networks are usually anchored in ministries. They may also include non-governmental and civil society organizations committed to promoting health and wellness through a One Health framework.

For example, many countries have separate databases to track outbreaks of infectious diseases in humans and animals. Connecting these systems between ministries and agencies can improve information exchange between them and gain a better understanding of spillover risks.

We believe that preparing for the next pandemic should include preventing it at its source. Our best chance of success is to coordinate research and design of spillover interventions, recognizing that human, animal and natural health are interconnected.

Written by:

Deborah Kochevar, professor of comparative pathobiology and dean emerita, Cummings School of Veterinary Medicine; Senior Fellow, The Fletcher School, Tufts University Guilherme Werneck, Professor of Epidemiology, Universidade Federal do Rio de Janeiro

This article was first published in The Conversation.