Future pandemics a real threat
Governments need to act to prevent zoonotic diseases from jumping from their animal hosts to humans, writes Sheree Bega
SURGING demand for wild meat, environmental destruction, climate change and intense, unsustainable farming could unleash future pandemics.
Unless governments act to prevent the transmission of zoonotic diseases such as Covid-19 from their animal hosts to humans, a steady stream of new outbreaks can be expected, a UN report warns.
Covid-19, which has already claimed more than 500 000 lives, is just one example of the growing number of zoonotic diseases, from Ebola and Mers to the West Nile and Rift Valley fevers, caused by viruses whose spread from animals to people has been amplified by the pressure humans place on the environment.
“The rising trend in zoonotic diseases is being spurred by the destruction of the natural environment through land degradation, wildlife exploitation, resource extraction, climate change and other stresses,” says the scientific assessment, Preventing the Next Pandemic: Zoonotic Diseases and How to Break the Chain of Transmission, jointly produced by the UN Environment Programme (Unep) and the International Livestock Research Institute.
These are wiping out natural habitats and seeing humanity exploit more species, bringing people into closer contact with disease vectors, writes Unep executive director Inger Andersen.
“Once established in humans, these diseases quickly spread across our interconnected world, as we have seen with Covid-19… This is a global challenge that nobody can hide from.”
The report is among the first to specifically focus on the environmental side of zoonotic disease outbreaks during the Covid-19 pandemic, seeking to “fill a critical knowledge gap”.
While pandemics like Covid-19 are sometimes seen as a black swan – an extremely rare event – “they are actually a widely predicted consequence of how people source food, trade animals and alter environments”, the report says.
About 60% of human infections are estimated to have an animal origin, and of all new and emerging human infectious diseases, 75% jump species, “interacting in unpredictable ways that can have negative outcomes”.
In the past 20 years, these zoonotic diseases have caused economic losses of more than $100 billion, with the cost of the Covid-19 pandemic expected to soar to $9 trillion over the next few years.
“Yet despite the massive real and potential socio-economic impacts of emerging zoonotic diseases and despite the general consensus that prevention is better than cure, investments and political will to control them at their source have been insufficient,” it says.
“Covid-19 has made us all aware it’s time to change that,” writes Jimmy Smith, the director general of the institute. “To prevent future outbreaks of novel zoonotic diseases, we need to address the root causes of their emergence. We need to break down silos, invest in public health programmes, farm sustainably, end the over-exploitation of wildlife, restore land and ecosystem health and reduce climate change.”
Each year two 2 million people, mostly in low- and middle-income countries with complex development problems, die from neglected zoonotic diseases, the report says.
Caradee Wright, a specialist scientist at the SA Medical Research Council who was one of a team of co-authors, says for South Africa, the report provides important guidance on how to prevent future zoonotic outbreaks.
“We experienced our own epidemic, the 2017-2018 listeriosis outbreak in South Africa – the largest outbreak of its kind in the world – and currently the Covid-19 pandemic is one of global concern,” she says.
“South Africa needs to keep its finger on the pulse of ecological systems and zoonotic diseases through continued surveillance, research and integrated policy support. We need to understand our food system in South
Africa – what are people eating, where are the sources, how is food being processed, stored and distributed.”
Social and economic issues that complicate the management of zoonotic disease, such as poverty, health-care inequity, waste management and the quadruple burden of disease faced by the population, must be considered.
The country can embrace its diversity and increase interconnectivity between all role-players in zoonotic management, “from environmental health practitioners, veterinarians and ecologists to small businesses selling animal products and community leaders, to strategically implement the ‘One Health’ approach promoted in this new report”, Wright says.
Rapid increases in the planet’s human population from a billion people 200 years ago to over 7.8billion today, has meant more encroachment of humans into natural habitats, says the report, raising the risk of animal-to-human disease transmission.
Deforestation, particularly in tropical regions, has been associated with an increase in infectious diseases, while climate change is another major factor.
“Many zoonoses are climate sensitive and a number of them will thrive in a warmer, wetter, more disaster-prone world foreseen in future scenarios,” it says.
It influences the future geographic distribution and abundance of species such as bats, monkeys and rodents, including those in which zoonotic pathogens often originate, and of mosquitoes and other vectors that transmit viruses.
While the coronavirus probably originated from bats in a market in Wuhan, China it is not yet known whether mutations allowed this jump from animals to humans and if so, which mutations were responsible, the report says. Some studies have suggested pangolins may have been the intermediate host.
In Asia and Africa, much wild meat as well as live wild animals are sold in informal markets.
“The lack of adequate biosafety measures makes these markets, where live wild animals are mixed together for their sale, a particular risk for zoonotic disease emergence,” it says.
Covid-19 may be associated with wildlife harvest, trade practices and the intensification in east Asia of wildlife farming, with the latter “actively encouraged” in some countries. By 2006, nearly 20000 wildlife breeding and farming ventures were established in China.
“There is concern that many wildlife farms are prone to low biosecurity and also enable illegally poached wildlife to be ‘laundered’ – presented and sold as legally farmed animals. Both factors would increase the risk of zoonotic disease outbreaks.”
While hunting has been part of many cultures for millennia, harvesting of wild animals is an important disease transmission interface between the environment and people. It’s estimated about 6 million metric tons of wild meat is harvested annually in Latin America and Africa. In central Africa, one analysis found meat supply from wild meat hunting might be higher (at 48g per person per day) than supply from domesticated animals (34g per person per day) while a recent survey of nearly 8 000 rural households in 24 countries across Africa, Latin America and Asia found that 39% of households harvested wild meat and almost all consumed it.
Behind the increasing consumption of wild meat in certain regions is an increasing human population demanding more protein-rich food and income that cannot be met with traditional resources alone.
Global population densities are increasing, especially in Africa, and local communities have few incentives to conserve wildlife and wildlife habitats.
“There are few attractive substitutes for these wildlife resources. The wild meat trade also serves as a safety net in times of hardship, as it generates both protein and income for poor households,” says the report.
One survey estimated that 83% of sampled households in Brazzaville, in Congo, consumed wild meat.
Disease transmission can occur through direct contact with hunted and consumed wild animals; traded wild animals (including at markets); wild animals kept as pets or in zoos, sanctuaries or laboratories and domestic animals.
“With wild vertebrates being reservoirs of a large repertoire of zoonotic pathogens, wild meat harvesting and trade in live animals enhances several pathways of zoonotic pathogen spillover,” the report adds.
Close contact between humans and different species of wildlife in the global wildlife trade can facilitate animal-to-human spillover of new viruses capable of infecting diverse host species.
“This can trigger emerging disease events with higher pandemic potential because these viruses are more likely to amplify via human-to-human transmission, and thus spread widely.”