As the planet warms, scientists are preparing for the spread of new and potentially lethal diseases.
The first case of the disease occurred in the Democratic Republic of the Congo’s remote south-west Kwango Province at the end of October 2024. Six weeks later, there was barely a family that had not been affected in Tsakala-Panzi, the epicentre of the epidemic. 169 people from the village got sick, the disease winding its way through the dusty paths that separate the frequently one-room houses. A feverish temperature, aching body, headache, cough, runny nose: the symptoms seemed to affect predominantly women and children. Just two weeks into the outbreak, the first death was recorded.
Neighbouring villages were getting ill too: Makitapanzi was hit with 142 cases of the unknown malady, while nearby Kanzanji had 78. Some of the patients had been taken to the hospital in Panzi, a basic operation opened under Belgium rule in 1960. Others died in their homes. What worried doctors most was not so much the severity of the sickness, which soon affected around 600 people across the district, but that the symptoms didn’t match any of the diseases that had affected locals in the past. Two years earlier there had been a typhoid outbreak in the area, but this wasn’t that.
The hospital lacked the facilities to test samples from the patients, and as numbers continued to snowball, the national health authorities in Kinshasa got wind of it. There was something airborne, something unexplained, circulating around Kwango: Could it be Disease X?
The World Health Organisation currently lists nine pathogens as a priority for research and resources—diseases that present the highest risk to world health, either in terms of their severity, their potential to spread or the challenges they would pose for containing an outbreak. Some will be familiar: Covid-19, Ebola, Zika and Severe Acute Respiratory Syndrome (SARS) are included, all of which have already caused pandemics or high-profile epidemics in recent years. Other pathogen families of grave concern have less recognition factor outside the public health fraternity or beyond a particular geography: Crimean-Congo haemorrhagic fever, Lassa fever, Nipah, Rift Valley fever. But it is WHO’s ninth priority that is its most mysterious.
Disease X is, by definition, an enigma, representing a pathogen that is not yet known to be an issue: "the monster at our door", Mike Davis, the late writer and theorist, called it in 2005. It could be bacterial or fungal, but it is most likely to be viral; it might be a mutation of something known or it could be a spillover from the animal kingdom. One thing is certain: the climate emergency, together with severe cuts in the WHO’s funding, has kicked the hinges off the door, inviting in another pandemic.
“Disease X raises awareness that there is something coming at some point in the future,” says Esther Hamblion, a British epidemiologist who leads the Public Health Intelligence Unit at the WHO. “You need a piece of terminology. What is it? We don’t know what it is. It’s Disease X.”
How do you prepare for something that hasn’t happened? How do you get funding for something that is by its very nature unknown? The question sounds like an existential riddle, an absurdity that would be comical if it was not so deadly serious.