The world may be at greater risk of infectious diseases that originate in wildlife because people are increasingly encroaching on natural habitats in the tropics to graze livestock and hunt wild animals. Devastating pandemics such as HIV/AIDS, Ebola, and COVID-19, all of which likely originated in wildlife, are reminders of how environmental destruction and infectious disease are intertwined. Tropical deforestation and overhunting are also at the root of global warming and mass species extinction.
All of these phenomena suggest that what we choose to eat has a fundamental impact on our health and that of the planet.
We recently conducted a review of the scientific literature to explore how wildlife-origin diseases, global warming, and mass species extinction are linked to the global food system. Our second objective was to explore reparative actions that governments, NGOs, and each one of us can undertake.
From the perspective of individual consumers, the global population needs to shift to diets low in livestock-sourced foods to stem human encroachment on tropical areas of wilderness. Second, there is a need to curb wildmeat demand in tropical cities.
Eating less foods from livestock
Closer to the equator, biodiversity becomes richer. These tropical regions have historically seen less development and are typically teeming with wildlife and carbon stored in the form of abundant vegetation. But in recent decades, agricultural frontiers have expanded rapidly into tropical forests. This unprecedented expansion of farmland for grazing and feed production may be increasing contact between wildlife, people, and livestock, which may enhance the likelihood of pathogens jumping from one to the other.
Such habitat destruction also has a negative impact on large herbivores and predators, as they lose sources of food and breeding grounds. This can lead to an increase in generalist species of rodents, bats, birds, and primates that are better adapted to thriving in human-modified landscapes. Some of these species are known reservoirs for infectious diseases of livestock and humans. For example, the white-footed mouse (Peromyscus leucopus) is a reservoir host for the bacterium Borrelia burgdorferi, which causes Lyme disease, while some fruit bats (family Pteropodidae) are reservoir hosts for Nipah virus and probably Ebola virus. Intensive livestock farms further increase the likelihood that domesticated animals can serve as intermediate hosts for wildlife-origin diseases, thereby amplifying the risk of human contagion. (See illustration on page 10.)
Flexitarian diets could feed the growing world population without further expanding farmland into tropical wildlands and with reductions in greenhouse gas emissions.
In addition, if the human population continues to grow and adopt diets rich in livestock-sourced foods, it’s unlikely that global warming can be kept well below 2°C and that the rate of species extinction can be slowed. This is because livestock production has the largest environmental footprint of all food production systems in terms of land and water use, greenhouse gas emissions, and pollution of terrestrial and aquatic systems.
Asking everyone to become vegan is not realistic or even desirable. But flexitarian diets could feed the growing world population without further expanding farmland into tropical wildlands and with reductions in greenhouse gas emissions. These diets consist of large amounts of plant-based foods, including vegetable proteins like pulses, nuts, and seeds; modest amounts of fish, poultry, eggs, and dairy; and small quantities of red meat and processed animal proteins.
Paired with conversion to environmentally friendly or organic farming and reductions in food losses and wastage, diets low in livestock-sourced foods are therefore a key component of a sustainable global food system. Such a dietary shift would have other public health benefits too, such as reducing overweight and obesity, diabetes, heart diseases, and colorectal cancer.
Measures available to governments, civil society, and businesses to promote healthier and more sustainable levels of consumption of livestock-sourced foods include education in schools, training of physicians and pediatricians, eco-labels on food packaging, taxation of meat and dairy products, a statutory duty for retail and hospitality sectors, and food procurement for workplaces, schools, and hospitals.
Governments tend to dodge such interventions for fear of public backlash. But the public tends to expect government leadership in tackling such a complex challenge.
Curbing wildmeat demand in tropical cities
In the tropical forests of Africa, Asia, and South America, hunting pressure to supply nearby cities has dramatically increased over the past 30 years. In addition to imperiling vulnerable animal populations, a vigorous wildmeat trade may increase the risk of zoonotic disease transmission.
But in the absence of effective state law enforcement and sustained campaigns to reduce consumer demand, bans do not work. In fact, consumers’ strong preferences for wild-meat mean that they may continue to purchase it despite price increases induced by a ban, boosting black markets. In the case of “luxury meat,” increased price and rarity may even drive higher demand. Bans could also shift the wildmeat trade to illegal, unregulated channels where less attention is paid to biosecurity measures necessary to prevent contagion from wildlife-borne diseases.
Outright bans can have other undesired effects. While in most large cities, legume, fish, and livestock-sourced proteins are easily available at affordable prices, there are Indigenous people and rural communities who rely on hunted meat for vital nutrition and income. Their rights to sustainably provision themselves within their customary territories should be safeguarded.
The ideal course of action would be to contain tropical wild- meat hunting and trade by curbing demand in urban areas and extractive outposts, while supporting hunting rights and biosecurity measures among communities in remote subsistence areas.
Avoiding biohazards from animal-sourced food
Interventions in rural communities should provide wildmeat hunters, traders, and butchers with training in inexpensive biosecurity measures they can easily adopt to avoid infection from contact with wild animals. Biosecurity measures should also be extended to livestock and wildlife farms, abattoirs, food markets, and restaurants. These measures include wearing protective clothing when handling wild animals, wrapping carcasses to prevent blood from contacting cuts in people’s skin, and cooking wildmeat thoroughly before eating.
Other physical distancing measures should be taken in farms, pastures, and live-animal markets. These include fencing and reducing livestock densities to minimize contact with wild herbivores, planting fruit trees visited by bats at a sufficient distance from livestock sites, and limiting the number of animals on sale in live-bird markets.
Different strategies across different regions
Levels of consumption of livestock-source foods, and the degree of reliance of human communities on animal-source proteins, vary dramatically. Efforts to reduce livestock production should focus on curbing excessive consumption in wealthier countries and expanding metro-polises in less developed and emerging economies. In the poorer rural areas of resource-limited countries, home gardening as well as smallholder livestock development programs can help decrease malnutrition with limited environmental and public health impacts.
Pastoralist communities in arid rangelands and hunter-gatherer communities in tropical rainforests and arctic locales that are inhospitable to crop cultivation would instead continue to rely on animals for nutrition. Nonetheless, the minor environmental impacts of their subsistence way of living are not comparable to those of dense and better-off urban populations.
Our future depends on urgent change
The incidence of infectious diseases originating in wild animals is high and may be increasing. This may be yet another warning signal that our degradation of ecosystems is undermining the capacity of planet Earth to sustain human health and well-being.
Dietary shifts away from livestock-sourced foods and reductions in tropical urban wildmeat demand are crucial to simultaneously protect the environment, safeguard resource-limited vulnerable communities, and reduce the risk of further disease outbreaks and pandemics. We all share the responsibility to act now to prevent pollution, floods, drought, famine, and epidemics from becoming increasingly prevalent.
Giulia Wegner is a socioenvironmental researcher at the Wildlife Conservation Research Unit (WildCRU) of the University of Oxford in the UK. Kris Murray is an associate professor in Environment and Health at the MRC Unit The Gambia and the MRC Centre for Global Infectious Disease Analysis at Imperial College London. Murray receives funding from the Medical Research Council UK, The Wellcome Trust, and the UK Global Challenges Research Fund. He currently serves as a scientific advisor/board member to the Soulsby Foundation and the Regenerative Society Foundation.