The last few years has made it abundantly clear that infectious diseases are not some abstract public health threat—they’re an ever-present and often unpredictable danger. We’re now in year three of the covid-19 pandemic, caused by the then-novel SARS-CoV-2 coronavirus. In May 2022, outbreaks of monkeypox began circulating across multiple countries, raising the possibility that this usually rare viral infection could become established in new parts of the world.
There are many other germs poised to become a more serious problem than they currently are. They’re what scientists call emerging diseases. These aren’t necessarily the next pandemic, but they could cause large outbreaks in the future or spread far beyond their present range. So here are eight of the most worrying emerging diseases out there.
The infection: Melioidosis is caused by the bacteria Burkholderia pseudomallei, which is typically found in tropical and subtropical environments.
Its threat potential: Melioidosis isn’t easy to diagnose or treat. And though it’s been confined to warmer parts of the world, it can spread through imported products like contaminated aquarium water or even aromatherapy sprays. Some experts fear that climate change will allow the bacteria to find new natural reservoirs in places like the U.S.
Symptoms and treatment: Symptoms vary, depending on how people are exposed to it. In people with a respiratory infection, for instance, it can cause fever, cough, and headache. It can be treated with extensive antibiotics, but its fatality rate can be high as 50%.
The infection: Candida auris, a yeast (microscopic fungi) pathogen.
Its threat potential: C. auris is routinely resistant to most or all antifungals, making treatment difficult. It can also quickly spread in areas where it’s most likely to cause serious illness, such as hospitals and other health care facilities. Though cases have remained rare worldwide since its discovery in 2009, they have been increasing over time, and the yeast is being found in new areas of the world every year.
Symptoms and treatment: Most people colonized by C. auris don’t become sick. But it can cause a widespread infection in already ill or immunocompromised individuals, often leading to sepsis and death.
The infection: Lyme disease is caused by certain Borrelia bacteria, which are transmitted by the bite of a female tick. In the U.S., the blacklegged tick (Ixodes scapularis) and the western blacklegged tick (Ixodes pacificus) are the primary vectors.
Its threat potential: Lyme and many other tickborne diseases in the U.S. have become more common over the past few decades. The ticks that transmit these diseases are also living longer into the winter and expanding their range beyond the Pacific and Northeast regions of the country, thanks in part to climate change, which will only expose more people to the disease.
Symptoms and treatment: Acute symptoms include fever, headache, fatigue, and a distinctive “bull’s eye” skin rash at the site of the tick bite. It can be treated with a few weeks of antibiotics, but untreated cases can result in more serious and possibly lifelong complications like arthritis and nerve pain.
The infection: Ebola, caused by four closely related species of the Ebola virus.
Its threat potential: In some ways, Ebola has gotten easier to manage, thanks to a recently developed preventative vaccine and antibody treatments. But outbreaks of the zoonotic disease have become more frequent in recent years as well. The Democratic Republic of Congo, for instance, is currently experiencing its sixth outbreak since 2018. Survivors of Ebola may also carry latent infections that can later cause new outbreaks.
Symptoms and treatment: Initial symptoms include fever, headache, muscle pain, and weakness, which can progress to diarrhea, vomiting, and heavy internal bleeding. In past outbreaks, its fatality rate has been as high as 90%, but newer treatments can now significantly reduce the odds of death.
The infection: Nipah virus.
Its threat potential: Nipah is primarily spread through fruit bats native to parts of Asia, including India, either from direct contact or droppings that can contaminate food and water. But it can spread sometimes between humans, and experts worry that regular outbreaks will one day allow the virus to evolve and become more contagious.
Symptoms and treatment: Fever, headache, and other flu-like symptoms at first. In more severe cases, the virus causes brain swelling and neurological complications like seizures and coma. Around 40% to 75% die from the infection, and there is no current specific treatment for it.
The infection: Dengue is caused by four types of the dengue virus, which are spread by Aedes aegypti and Aedes albopictus mosquitoes.
Its threat potential: The reported incidence of Dengue has increased dramatically over the past two decades, and regular outbreaks have been documented in previously unestablished areas of Europe and the Americas. A vaccine does exist, but it isn’t recommended for people who haven’t been infected before, since it may raise the risk of severe dengue in those never exposed to any type of the virus.
Symptoms and treatment: About a quarter of victims will experience symptoms, which include fever, muscles aches, eye pain, and rashes. Surviving one type of dengue infection will not confer protection to the others, however, and a second infection increases the risk of a severe, life-threatening illness that can kill within hours.
The infection: Measles, caused by the measles morbillivirus.
Its threat potential: Measles is an example of a re-emerging disease. The extremely contagious infection was once considered a prime candidate for eradication, thanks to a highly effective childhood vaccine. But declining vaccination rates have allowed measles to regain a foothold in many parts of the world, and experts fear that 2022 will see very high case numbers once again.
Symptoms and treatment: High fever, cough, and a distinctive rash that covers the body. It’s only rarely fatal, though moreso in younger children. But even in survivors, it can cause a rare neurological condition years after infection or effectively reset people’s immune memory to other infections, causing them to be susceptible once again. No specific treatment exists for it, though symptoms usually go away on their own within several weeks.
The infection: Avian influenza, caused by strains of influenza A viruses native to birds.
Its threat potential: Highly pathogenic avian flu strains can be incredibly transmissible and fast-killing among wild and domestic birds. Since last October, an epidemic caused by an avian H5N1 strain has spread across the globe, leading to the deaths of millions of birds. Bird-to-human transmission of these germs is uncommon, usually requiring close, prolonged contact, and it’s even rarer that someone will then spread the infection to others. But over time, the worry is that one of these strains will pick up the right set of mutations that allow it to be just as contagious and fatal in humans as it can in birds, setting the stage for a horrific pandemic.
Symptoms and treatment: Humans usually don’t get sick from avian influenza viruses, but symptoms can resemble the typical respiratory infection. Some past outbreaks in humans have been especially deadly, however, killing close to half of those infected.