Scientifically Speaking | Countering "Disease X": A plan for the unseen threat
Scientists study prototype pathogens within known viral families, providing a headstart in creating treatments and vaccines for the unforeseen "pathogen X."
In September 2023, India faced a concerning outbreak of the Nipah virus in Kerala's Kozhikode district. This incident marked India's sixth Nipah virus outbreak since 2001. The ministry of health and family welfare reported six confirmed cases, including two deaths. The first case's infection source remains unknown, while the others were either family or hospital contacts. By September 27, authorities had identified and quarantined 1,288 people, including healthcare workers and high-risk contacts. Fortunately, no new cases emerged after September 15.
Nipah virus can be transmitted to humans through contact with infected animals, such as bats and pigs. It can also spread from person to person, though this is less common. Infected individuals can experience acute respiratory infection and neurological signs, including encephalitis, which can be fatal. The disease has a high fatality rate ranging from 40% to 100% depending on the strain.
The high mortality rate of Nipah infections, coupled with the lack of effective treatments or vaccines, makes the causative virus worrisome enough to be included in the World Health Organization (WHO) list of priority pathogens.
This outbreak in Kerala is a stark reminder of the ongoing threat of emerging infectious diseases and the need for vigilance and preparedness. The Nipah virus is highly lethal. Fortunately, it is less contagious than many other viruses.
Transmission of Nipah primarily occurs through direct contact with infected animals, such as bats and pigs, or by consuming food contaminated with the virus. Human-to-human transmission, though less common, can occur, particularly in a healthcare setting or through close contact with an infected individual.
Two months after the outbreak of Nipah in India, Cambodia faced an outbreak of avian influenza A (H5N1). The first patient sought help after developing symptoms but unfortunately passed away. The second patient was identified during active surveillance in response to the first case. Both patients had contact with backyard birds reported to be sick or dead.
H5N1 virus typically transmits to humans through direct contact with infected animals or contaminated environments. Since 2003, there have been at least 62 cases and 41 deaths from H5N1 in Cambodia. The virus is highly lethal but not easily transmissible in humans.
A virus that is lethal and spreads easily represents a doomsday scenario. Unfortunately, each spillover event of Nipah and H5N1 represents an opportunity for these viruses to mutate to gain the ability to become more transmissible in people.
With humans increasingly encroaching on areas populated by animals and with climate change bringing new infectious diseases to new locations, we will likely see more outbreaks.
Where will the next pandemic come from? We must show humility and admit that we cannot know for sure. However, we can prepare even without precise knowledge.
Humans are susceptible to disease-causing infections by around 150 viruses that belong to 26 virus families. Since 1900, five pandemics have occurred, all linked to influenza or coronaviruses. Coronaviruses were considered minor threats until the 2002 SARS outbreak and the 2015 MERS emergence. Indeed, the scale of the 2020 Covid-19 pandemic was unexpected and many of the measures that were employed were taken from the playbook for an anticipated influenza pandemic.
Last week, world leaders convened at the World Economic Forum in Davos, Switzerland to discuss "Disease X," a deadly disease that could cause the next global pandemic. This meeting, led by WHO chief Tedros Adhanom Ghebreyesus, aimed to prepare healthcare systems for future challenges, recognizing that “Disease X” could result in a loss of life vastly exceeding that of COVID-19.
"Disease X" was added to the WHO's list of priority diseases in 2018, alongside known threats like Ebola, Nipah, and Zika. This list helps identify diseases with significant epidemic potential and limited existing countermeasures. The WHO, drawing on the expertise of over 300 scientists, is reviewing this list in 2024 and incorporating lessons learned from the COVID-19 pandemic.
"Disease X" represents an unforeseen yet significant threat. It's likely to originate from a "pathogen X” which will most likely spill over from animals to humans. Easy human-to-human transmission might make the virus difficult to contain.
Because viruses (like influenza viruses and coronaviruses) that contain RNA as genetic material make mistakes when they replicate, they represent perhaps the greatest risk. Respiratory viruses are also much harder to contain compared to viruses that require close and sustained contact or exchange of body fluids.
The WHO emphasises the large number of potential pathogens and the limited resources for research and development. Targeting priority pathogens might help us to respond to epidemics and pandemics.
But what about “Disease X”? How can we respond to a threat that doesn’t exist yet? Here also there is a plan. While the number of new viral diseases has been increasing steadily over the years, the actual number of viral families they belong to has remained stable. For example, we knew about the coronavirus family, even before the virus that caused COVID-19 was discovered.
For each family of viruses that currently infects people, scientists are identifying prototype pathogens which are representative of the family. It’s possible that “pathogen X” which will cause “Disease X” will come from one of these known families. By studying these prototype pathogens and creating treatments and vaccines right now, we can get a head start once the next major threat arrives.
There is no room for complacency. We don’t know when and where it will start, but the next pandemic will happen. We must be better prepared for it.
Anirban Mahapatra is a scientist and author. His second popular science book, When The Drugs Don’t Work: The Hidden Pandemic That Could End Medicine, will be published this year. The views expressed are personal.