The mysteriously named Disease X has the potential to become the next big pandemic, a doctor has warned, while also claiming the world isn’t prepared for a sudden boom in cases.
Disease X – which is essentially the name given to an as-yet-unknown infection – was among 11 other dangerous diseases that doctors were most concerned about for the year ahead. Measles, cholera, scabies, bird flu, and even another Covid outbreak were also included in the list of scientists’ most feared infections for 2025.
The World Health Organization (WHO) had previously dubbed unknown pathogens as Disease X, and it was included in its own priority list of diseases that needed urgent research. It’s most recently killed at least 31 people – mainly children – in the Panzi region of the Democratic Republic of Congo (DRC).
The WHO said there were more than 400 recorded cases of an undiagnosed disease in the DRC between October 24 and December 5. The most common symptoms included fever, headache, body aches, and a bad cough. But, the most severe cases were often linked to severe malnutrition, it said.
Disease X is one of the infections that’s most likely to lead to severe outbreaks, and possibly even a pandemic, according to Dr Michael Head; Senior Research Fellow in Global Health at the University of Southampton. If an outbreak were to appear immediately, the world would likely be incredibly unprepared, in a similar vein to the international shock of coronavirus.
Disease X
Disease X isn’t an actual infection – it’s more the name given to any disease that hasn’t been identified, so far. But, the idea of an unknown virus or bacterial infection is very real, and scientists have urged governments to be prepared for anything Mother Nature might throw at us.
“Disease X is the name given to an as-yet-unknown bug, that has the potential to cause large outbreaks or even a pandemic,” Dr Head told the Mirror. “This bug would have the potential to spread quickly and have a high mortality rate; for example like COVID-19.
“The world was poorly prepared for the most recent pandemic, and though we have significant advances in technology, such as the use of mRNA platforms for vaccines and other medicines, we would likely fall short again should Disease X emerge tomorrow.”
- Symptoms: Who knows? It could include anything dependent on its biological make-up. If it were a respiratory virus, it could cause coughs or difficulty breathing. But if it were a bacterial infection, it might cause more stomach bug-like symptoms.
Dengue
Dengue fever is the world’s most commonly transmitted virus by mosquitoes. Tens of millions of cases are reported every year, and up to 25,000 people die annually.
It’s most commonly found in South America and Southeast Asia, but more and more cases are cropping up in southern Europe – mainly driven by climate change. France, Italy and Spain are most likely to see outbreaks of dengue – which is commonly referred to as the ‘bone breaker’ disease.
The mosquito that carries the virus is eventually expected to gain a foothold in the UK, although it’s still unclear exactly when that might be. Medicine professor at the University of East Anglia, Paul Hunter, expected to see more cases of dengue fever in 2025 – particularly in southern Europe.
- Symptoms: The virus usually causes flu-like symptoms, including a fever, headaches, joint pain, and a characteristic rash mad eup of slightly raised spots. In the most severe cases, it could lead to bleeding gums, repeated vomiting, and severe stomach pain.
Chikungunya
There was only one confirmed case of chikungunya in Europe in 2024, but it could be on the rise in the coming year, warned Professor Hunter. It’s another mosquito-driven viral infection, and is similar to the mayaro virus and the ross river virus.
Almost all cases of the virus are found in South America; particularly in Brazil, which had more than 400,000 between August and October in 2024. But, European climates are becoming more favourable for mosquitoes, and scientists fear chikungunya could be on the rise.
Professor Hunter said: “I think we will likely see more mosquito-borne diseases in southern Europe; mainly dengue but also probably chikungunya. I also worry about West Nile fever.”
- Symptoms: Most people with chikungunya develop joint pain and a fever about five days after the initial infection. Patients tend to feel better after a week, but it could lead to severe and debilitating joint pain that lasts for months.
West Nile fever
The West Nile virus goes completely unnoticed for about 80% of human patients. But for those remaining 20%, it can lead to deadly West Nile fever. The virus is transmitted by mosquito bite, although it could also be spread by blood transfusions and organ transplants. It’s yet to be reported by local transmission in the UK, but there have been cases of travellers returning with the infection.
Human infections have, however, been reported in Spain, France, Italy, Greece, and Germany since the start of November 2024. At its worst, West Nile fever can develop into West Nile neuroinvasive disease (WNND). WNND describes when the nervous system is directly affected by the virus, and it can include developing meningitis, encephalitis, and acute flaccid myelitis.
- Symptoms: Headaches, fevers, fatigue, and swollen glands are the most common signs of West Nile fever. Some patients might also develop an itchy skin rash that appears on the back, arms, or trunk of the body.
Measles
Measles is a very serious airborne infection that mainly affects young children. More than 107,000 people died from measles globally in 2023, a majority of whom were under fives years old. It’s spread simply by coughing or sneezing, moving in air droplets, and can live in the air or on surfaces for up to two hours. That makes it highly infectious, and infects about 90% of all unvaccinated people within close contact. Measles has been on the rise in the western world over the past few years, largely driven by a fall in vaccination rates. The proportion of kids receiving their first dose of the measles vaccine in 2019 was 86%. But that fell to 83% in 2023.
Dr Head said: “Measles is vaccine-preventable. With two doses of the MMR vaccine, that stops measles in its tracks. With a high uptake, we could literally eradicate it from the planet, like smallpox. A lower uptake, partly due to too much covid interrupting health service delivery in the pandemic, means children in the UK and globally are being affected. It is a nasty infection in unvaccinated children, and it can and does kill.”
- Symptoms: The infection usually starts with flu-like symptoms, before the patient develops the characteristic ‘measles rash’. It includes raised spots that join together to make large blotchy patches of skin, and spreads from the face to the rest of the body.
Covid
Coronavirus never went away, and it’s still been bubbling away in the background. Even worse, it’s still mutating and changing, with new strains harbouring the potential to become more infectious and – dare we say it – vaccine-resistant.
In October this year, the UK Health Security Agency (UKHSA) confirmed a new variant appeared to be more infectious than previous strains. The XEC variant, which combined strains of KS.1.1 and KP.3.3 suddenly sparked a big rise in Covid cases across the country. Admission rates for people testing positive for Covid rose from 3.7 per 100,000 to 4.5 per 100,000 in just one week.
Dr Head said: “The vaccines, along with use of medicines and diagnostics etc., have massively blunted the public health impact of COVID-19. But, it’s still here, very much hasn’t gone away, and will continue to pose a problem to health services and populations everywhere around the world. Do get vaccinated if another dose if offered to you!”
- Symptoms: The three key signs of Covid have remained the same for a number of years now, and there’s no early signs of any variants causing unique symptoms. A continuous cough, high fever, or change to your sense of smell or taste could all be signs of coronavirus. Some people might also develop fatigue, a sore throat, headaches, diarrhoea, nausea, and general cold-like symptoms.
Cholera
Cholera is a global public health threat, the WHO warned. It’s a severe diarrhoeal disease that’s caused by consuming food or water contaminated with Vibrio cholerae bacteria. In the most extreme cases, the infection can develop very, very fast, leading to death within a few hours if not treated. Up to 143,000 people die from cholera each year worldwide.
There have been seven cholera pandemics since in the 19th century, with the most recent in 1961 largely affecting south Asia. But forced migration, sparked by climate change, could mean that 2025 sees another big surge in cholera cases, warned Professor Hunter. Still, cholera cases are incredibly rare in Europe, and most confirmed cases are found in Africa and Asia. In 2022, for example, 29 cases were reported by nine EU countries; all of which included a history of travel to a cholera hotspot.
- Symptoms: The most common sign of cholera is having lots of watery diarrhoea. It might be accompanied by severe vomiting and stomach pain, and subsequently leads to dehydration.
Bird flu
Avian flu, or bird flu as it’s more commonly known, is widely accepted as the most likely known cause of the next pandemic. It’s a type of flu virus that commonly spreads among birds, but has been known to jump across to humans. The virus isn’t easily passed to humans, however, although it can mutate rapidly, leaving scientists fearing a mass outbreak. As it stands, almost all cases of H5N1 – the most common bird flu strain in humans – have been reported in those that work closely with animals.
“A permanent member of any ‘possible infectious disease threat’ list, avian influenza evolves its shape and style a little like the Covid variants, and has the potential to cause a pandemic,” said Dr Head. “We haven’t yet seen widespread human-to-human transmission – but we could do.”
Bird flu is spread to humans by touching infected animals, their droppings or bedding, or by preparing infected poultry for cooking. There isn’t a seasonal bird flu vaccine, but a universal jab to protect against all types of flu, including avian flu, would be the “holy grail”, added Dr Head.
- Symptoms: A very high fever is the earliest sign of a bird flu infection, combined with fatigue and a painful headche. Some patients have also previously reported severe conjunctivitis or bleeding from the nose or gums.
Antimicrobial-resistant bacteria
UKHSA has warned that antibiotic-resistant infections continue to rise in the UK, while the WHO said antimicrobial resistance is a top global health threat. Antimicrobials are medicines commonly used to treat infectious diseases, including antibiotics, antivirals and antifungals. But scientists have warned that these infections are taking increasingly longer to react to the medications, as they’re evolving and developing to protect against them.
Anyone that gets a bacterial infection that’s resistant to antibiotics are more likely to die within 30 days, according to the UKHSA. Professor Hunter added that antimicrobial-resistant bacteria posed a “significant concern” going into 2025. E.coli is by far the most common type of antibiotic-resistant bacteria in the UK, which commonly causes diarrhoea, vomiting, and urinary tract infections. By the middle of 2024, the UK reported more than 600 cases of the bacteria, which was markedly more than seen in previous years.
UKHSA Chief Executive, Professor Dame Jenny Harries, said in November: “Increasingly the first antibiotics that patients receive aren’t effective at tackling their infections. That’s not just an inconvenience – it means they are at greater risk of developing a severe infection and sepsis. Our declining ability to treat and prevent infections is having an increasing impact, particularly on our poorest communities.
“Only take antibiotics if you have been told to do so by a healthcare professional. Do not save some for later or share them with friends and family. This isn’t just for your own health – it’s about protecting everyone in our communities and future generations.”
- Symptoms: The signs of infection vary dependent on the bacterial or viral infection. E.coli infection, however, can cause bloody diarrhoea, vomiting, stomach cramps, and cystitis.
Whooping cough
Pertussis, or whooping cough, is a bacterial infection that affects the lungs, and can be deadly if left untreated. It mainly affects young children and babies, but any can develop symptoms if they become infected.
The infection is named after the characteristic ‘whoop’ sound made by infected young babies between deep breaths. But, not all babies make the noise, which means it can go untreated for some time.
The UK is in the midst of a major whooping cough outbreak, and annual confirmed cases topped 10,000 in August. The second quarter of the year saw more confirmed cases than any of the quarters in 2012, which was the last major outbreak year.
Professor Hunter said it remained unclear whether there would be more cases of whooping cough in 2025 than 2024, but it remained a “big concern”. At least 10 infants have died in the UK since the start of the current outbreak, which dates back to November 2023.
UKHSA’s Director of Immunisation, Dr Mary Ramsay, said earlier this year: “Vaccination is the best defence against whooping cough and it is vital that pregnant women and young infants receive their vaccines at the right time. Pregnant women are offered a whooping cough vaccine in every pregnancy, ideally between 20 and 32 weeks.
“This passes protection to their baby in the womb so that they are protected from birth in the first months of their life when they are most vulnerable and before they can receive their own vaccines.”
- Symptoms: The very first symptoms of whooping cough are similar to a normal cold, including a runny nose and sore throat. After about a week, it could develop into coughing bouts, difficulty breathing, and bringing up thick mucus.
Scabies
Doctors have recently urged the British public to avoid ignoring the signs of scabies infestation, after a spike in cases. The condition is casued by tiny mites burrowing into the skin to lay their eggs, sparking a really unpleasant itchy rash.
Scabies doesn’t killy many people, but it can really affect your quality of life, according to Dr Head. It’s particularly common in the UK, and is mainly seen in institutional settings, including schools, care homes, and prisons.
The number of confirmed scabies cases in England increased by 58% in the first half of 2024, compared with 2023. GP diagnoses were also well above the five-year average, with the north of England seeing the largest proportion of cases.
“The mites burrow under the skin, causing an immune response that triggers inflammation and itching,” said Dr Head. “You can catch it by prolonged skin-to-skin contact, or via clothes, furniture or bedding that an infected person may have used previously.”
- Symptoms: Intense itching is the most obvious sign of scabies – particularly at nighttime. You might also develop a rash with lined-up red spots, showing where the mite has left its eggs. The rash is common between the fingers, and may eventually turn into dark spots.