Disease X

Sophie Cousins

Health officials in Kerala have confirmed a number of deaths from Nipah virus in the south Indian state. In the Democratic Republic of Congo, there is an outbreak of Ebola. Earlier this year, a team of virologists, bacteriologists and infectious disease experts met at the World Health Organisation’s headquarters in Geneva to determine which diseases and pathogens pose the greatest public health risk because of their epidemic potential and an absence of effective drugs and vaccines for treatment and prevention. Both Nipah and Ebola are on the list.

The 2018 Research and Development Blueprint, released in March, also includes Zika virus, Lassa fever (a viral haemorrhagic disease occurring primarily in West Africa), MERS-CoV and Sars – and something called Disease X.

Disease X isn’t the name of a mysterious new disease that you’ve never heard of. Rather, ‘Disease X represents the knowledge that a serious international epidemic could be caused by a pathogen currently unknown to cause human disease,’ the WHO said.

The West African Ebola outbreak of 2014 demonstrated not only how unprepared the world is to combat a public health emergency, but also how an old disease, that's fallen off the radar, can suddenly reappear, spread rapidly and cause serious damage. The WHO faced widespread criticism for its slow response to the Ebola epidemic, which killed more than 10,000 people. The R&D Blueprint was created as a result.

Much of the media quickly labelled Disease X a ‘mystery killer’, and speculated that it could come from a deliberate attack, from North Korea or Syria using bioweapons. But Amesh Adalja, at the Johns Hopkins University Centre for Health Security, thinks Disease X is more likely to be a respiratory-spread virus, which has the ‘highest pandemic potential’. In particular, it could be an RNA virus – like Influenza A – because they have high mutation rates. It’s also likely to spread to humans from animals: 70 per cent of new diseases are zoonotic.

‘When you look at all the different pathogens, viruses jump to the top because we don’t have counter measures against them,’ Adalja told me. ‘When you think about how respiratory viruses are spread – through breathing – it’s very hard for public health measures to intervene.’

We have broad spectrum antibiotics (though there’s increasing resistance against them) to fight bacteria, but there are very few effective broad spectrum antiviral drugs. Most antivirals are used for specific infections, not against a wide range. Some viruses, such as Zika and MERS, have no specific treatment or vaccine.

As well as getting better at diagnosing infectious disease symptoms quickly and reporting them to the relevant authorities, Adalja says we need broad spectrum antivirals. ‘The Ebola outbreak was a major turning point because lots of antivirals in experimental use came forward,’ Adalja said. ‘We have promising candidates from this experience.’

We also need to prepare by strengthening health systems: more laboratories to diagnose diseases, more trained healthcare workers, better use of technology. And we need to drop any preconceptions that Disease X will emerge in the developing world: we don’t know where the next pandemic will come from. Finally, if this all seems alarmist, it’s important to remember that forty years ago, Disease X was HIV.


  • 22 May 2018 at 7:36am
    David Gordon says:
    "WHO faced widespread criticism for its slow response to the Ebola epidemic". Well indeed - but at one stage the problem was that member states of WHO where the Ebola epidemic was starting to rage wanted WHO to say nothing publicly to protect what they saw as national interests. Then, when it was inescapable that something had to be said, WHO got the blame for the delay.