When Cyclone Yaku hit the northern coast of Peru in March 2023, it unleashed hurricane-force winds and torrents of rain, triggering landslides and flooding. Then came El Niño, a periodic warming of eastern Pacific Ocean surface waters, boosting rainfall and fomenting an explosion of pool-breeding Aedes aegypti mosquitoes, the main vector of dengue fever. The ensuing outbreak of dengue – a viral infection that causes high temperature, headaches, vomiting and joint pain – may also have been given added momentum by climate change. At higher temperatures, the mosquitoes bite more often, egg-hatching speeds up, and the dengue virus itself replicates faster. By late June, 2023, more than 160,000 people in Peru had been infected with dengue and 287 had died.
Dengue, warns John Vidal in Fevered Planet, “is perfectly suited to spread fast in a warming, more humid, urbanised world”. And it is one of many such maladies that thrive in an era of climate crisis and environmental degradation.
Travelling from Gabon to the Arctic Circle and many places in between, Vidal, a long-time environment editor at the Guardian, documents the rise and spread of infections that are thought to have leapt from animals to humans, including Covid-19, Ebola, HIV/Aids, mpox, Mers, and Sars. He argues, convincingly, that by exploiting the world’s resources and damaging natural habitats, we create the conditions for diseases like these to emerge. Even so, he says, there’s still time to reverse some of the harm.
Take Ebola, for example. The virus that causes this often-fatal haemorrhagic fever first emerged in 1976 in a village near the Ebola River in the Democratic Republic of the Congo (then Zaire). Ebola’s most likely “host reservoir” is a bat. As Vidal notes, such jumps from animals to humans often occur at the degraded edges of the world’s tropical forests. As humans encroach, they increasingly come into contact with unfamiliar wildlife, and are prey to the diseases it carries. As a 2017 study showed, from 2004 to 2014, spillovers of Ebola from wildlife to humans in west and central Africa occurred mostly in “hotspots of forest fragmentation”.
In vivid prose, Vidal describes the devastation that followed when a rare moabi tree in the Congolese rainforest – 60 metres tall and 200 years old – was felled for the timber trade. “For several minutes the stricken moabi seemed to rain birds, flies, seeds, spores, leaves, bees, flowers, wasps, nests, ants, beetles, moths, frogs, snails, and all the thousands of insects and small mammals that had lived together in that tree,” he writes. “Anything that could, flew. Everything else ran, crawled, burrowed, hid or took its chances. A complete ecosystem with thousands of interdependent organisms had been transformed in a few moments.”
In 2022, about 4.1m hectares of tropical primary rainforests were destroyed, equivalent to a rate of 11 football pitches a minute, according to data compiled by the World Resources Institute. Transforming forest to farmland or flooding large areas to build dams increases the risk of zoonotic (animal-borne) diseases leaping to humans. Biting insects such as mosquitoes, ticks, flies and fleas all thrive in ecologically-disturbed areas, and are linked to at least 16 infectious diseases, including malaria, dengue, yellow fever and Lyme.
Vidal quotes wildlife epidemiologist Christine Kreuder Johnson, director of the Institute for Pandemic Intelligence at the University of California, Davis. In a paper published in 2020, she and her colleagues found that threatened, exploited and hunted wildlife species shared more viruses with humans. Bats have been implicated as a source of Sars, Nipah virus, Marburg virus and ebolaviruses, as well as Covid-19, although the latter’s exact origin continues to be obscured by controversy.
Vidal’s research is so comprehensive, and his lists of contagions so extensive, that after a while I began to wonder whether our cat, Pebbles, was about to give me roundworms or cat scratch disease. (“So far there have been no major epidemics or pandemics starting in the home,” he writes. Phew.) But petting zoos and ecotourism have been linked to outbreaks of salmonellosis and meningitis, and ostrich farms in South Africa to the emergence of avian flu.
Fortunately there is some hope. Currently, the health of people, animals and the planet are treated as separate issues. But as Vidal shows, they are intimately linked. What is needed is not merely the “whack-a-mole” approach to pandemics – “identifying, quarantining and isolating infected people” and vaccination where possible – but a “radical new approach to ensuring global health”, including preparing for disease by surveying the places it is most likely to strike.
The Global Virome Project, for example, is a $4bn plan to genetically record and build an atlas of all the viruses that might threaten humanity. Ultimately, we need to recognise that our own impact on the world – including wanton deforestation and erosion of biodiversity – drives many of these outbreaks. Our assault upon the planet plagues us in return.
• Fevered Planet: How Diseases Emerge When We Harm Nature is published by Bloomsbury (£20). To support the Guardian and Observer, order your copy at guardianbookshop.com. Delivery charges may apply.
