In the past three weeks there have been nearly 100 cases and 18 human deaths from a rare tick-borne disease in Iraq; a fourth case of the Ebola virus and more than 100 cases of bubonic plague have been found in the Democratic Republic of Congo; and just two years after Africa was declared free of wild polio, new cases have turned up in Malawi and Mozambique. A dangerous strain of typhus is circulating in Nepal, India and China. There are alarming outbreaks on several continents of mosquito diseases such as malaria, dengue and West Nile virus.
Set against this global context, the so-far very limited monkeypox outbreaks that have started to appear in the last month – including 71 cases detected in the UK – are only remarkable because they are being reported in rich countries.
It has been a bad month for infectious disease, according to the ProMED website, the world’s largest open surveillance system for reporting outbreaks. Covid and HIV are both still globally rampant, and now animal pandemics are on the march, too. African swine fever continues to ravage the world’s pigs and several strains of lethal avian – or bird flu – are spreading, forcing the cull of hundreds of millions of poultry. Vets and ecologists have warned this month, too, of mysterious fungal diseases being found in fish and marine life in Australia and in Middle Eastern countries, well as lethal dog and other pet illnesses.
We live uneasily with many thousands of potentially fatal viruses circulating in other species, but what is remarkable is that most of those that affect humans today were unknown just 70 years ago. Not only are new pathogens jumping from animals to humans more often, but an increasing number are linked to the changes in the global and local environments.
It is no coincidence that since 1940, 335 new and potentially fatal diseases have emerged globally, over a period when the human population has trebled, the climate has changed and more meat is being eaten. Disease ecologists say that nothing increases the risk of a crossover of a pathogen from one species to another like the uncontrolled expansion of farming, and the exploitation by humans of wild species.
It is now payback time for nature. The more human numbers have grown and we have encroached on wild spaces or imposed unnatural conditions on other species, the more we have created the ideal environments for viruses and pathogens to spill across species, mutate and spread. HIV, Ebola, Lassa fever and monkey pox in Africa; Sars and Covid-19 in China; Chagas, Machupo and Hantavirus in Latin America; Hendra in Australia; Mers in Saudi Arabia – all have all emerged in the past 75 years just as we have accelerated deforestation, moved to cities, come closer to animals and created a global economy.
Most worrying for humans is not monkeypox, plague or even Ebola, which sound dangerous and exotic but are actually more or less controllable now with vaccines. Instead, the threat of a new bird flu, just as likely to come out of a farm in New York or England as one in China or Bolivia, now stalks humanity. Chicken is now the rich world’s most popular meat and tens of millions of near-genetically identical birds prone to catastrophic disease are being mass-reared at any one time, often in unhygienic conditions, and are able to mix with wild birds. It is only a matter of decades before a new highly pathogenic avian influenza strain evolves to be easily transmissible between humans.
As much by luck as good judgment, humans dodged a bullet with Sars in 2003 and to some extent with Covid, which so far has killed about 1% of people infected. But major flu pandemics with very high mortality rates come along every 30 years or so and we are well overdue the next. If we are lucky we will find a vaccine fast and it will only kill 10-20% of people it infects. If we are unlucky, it could be just as transmissible as Omicron and as fatal as Ebola – in which case it would effectively be game over for much of humanity and the global economy.
But we may have seen nothing yet. Climate change is now kicking in, creating a hotter, sicker world with a potentially catastrophic impact on disease. Global heating fundamentally changes the landscape of disease by forcing or enabling species to survive in new places and mix with others. Insects already kill about 700,000 people a year, but global heating allows mosquitoes, mites, fleas, ticks and other vectors to flourish in new areas, spreading dengue, chikungunya, and other diseases to higher ground or to previously cooler climates.
Canadian bacteriologists have shown how in times of great historical environmental change – like now – pathogens jump more easily to new, susceptible hosts. All they need is the opportunity for contact, and warming does just that. Once they have expanded to new hosts, novel variants are more likely to emerge, each with new infection capacities.
The situation looks bleak, but it is well within human ability to repair and turn this round. Science and new technologies are catching up with vaccines for rare and neglected diseases, and global surveillance and the early detection of potential virus spillovers in the wild can be greatly enhanced. But above all, global finance can be directed to improve creaking public health systems, especially in developing countries. They are the first line of defence and the surest precaution of disease containment.
The big lesson of Covid – and now of monkeypox – is that much infectious disease has its roots in ecological change. That means the health of the planet and the health of humans and must be considered alongside that of animals. It also means we should prepare now for the unexpected, invest in public health as never before, stop cutting down the forests, address climate change and phase out intensive farming. A “one health”, planetary approach to health is the best – and possibly the only – hope we have.
• John Vidal is a former Guardian environment editor
