Brain-eating amoebas are spreading—and that’s just as bad as it sounds

Here's everything you never wanted to know about the subject.
naegleria fowleri brain amoeba
The amoeba in question CDC

Nothing strikes fear and paranoia into the public’s heart like the phrase “brain-eating amoeba.” Those ominous words dominated headlines this weekend as news spread of a 29-year-old man who contracted the disease and died after visiting a surf park in Waco, Texas.

Fabrizio Stabile began feeling unwell and developed a headache while mowing his lawn days after visiting the park, which is part of what’s so dangerous about this disease: it starts off seeming quite benign. Stabile eventually couldn’t get out of bed or form coherent speech, at which point he was rushed to the hospital. Doctors couldn’t save him. It’s a terrifying story, which is why it’s making headlines, but how scared should you be? Here’s what you need to know.

It’s a kind of meningitis

The particular kind of brain-eating amoeba in this story is called Naegleria fowleri. But let’s back up a bit and begin with what an amoeba actually is. Amoebas are single-celled organisms, but the word is also kind of a blanket term for an organism that has no defined shape and moves by squishing around its cytoplasm (that’s the gel-like stuff that fills cells). Not all of them cause disease, and in fact many of the other amoebas in the Naegleria genus don’t pose any threat to humans.

N. fowleri, however, can enter the human body through the nasal cavity, where it attaches to the olfactory nerves and migrates into the brain. There, it causes inflammation that you might know better as meningitis. The term “meningitis” just means inflammation of the meninges, which are the membranes surrounding your brain and spinal column. At some point you (hopefully) got a meningitis vaccine, but that only protects you against three types of bacterial meningitis. Viruses, parasites, fungi, and amoebas can also cause this inflammation.

Any of these sources can be deadly, but amoebic meningitis is generally more dangerous than the more-common viral or bacterial varieties because there’s no clear treatment. We have potent antibiotics and antivirals. We don’t have the same options for killing amoebas.

It’s exceedingly rare, yet also common

The world has only even known about amoebic meningitis since the 1960s, when researchers identified N. fowleri as the cause of infections in the U.S. and Australia. A few historical cases were recognized in retrospect, but between 1962 and 2015 there were only 138 cases in the U.S., or between 0 and 8 cases every year. Australia, the other country with thorough data on N. fowleri infections, has had a similarly small number of reported cases. Worldwide estimates of total cases to-date range from 235 to 300.

This is despite the fact that the offending amoeba is ubiquitous in soil and warm water around the world. The Mayo Clinic notes that “millions of people are exposed to the amoeba that causes naegleria infection each year, but only a handful of them ever get sick from it,” and that experts aren’t sure why certain people contract the disease while others don’t.

It really does eat your brain

As the amoeba grows, it “multiplies by feeding on nerve tissue,” according to a horrifying 2012 overview of the disease. On top of the damage inflicting by that consumption, N. fowleri also induces inflammation, necrosis (tissue death), and internal bleeding. It is exactly as awful as it sounds.

It’s found in warm water, including in neti pots

N. fowleri lives in warm, fresh bodies of water—everything from luxurious hot springs to mundane tap water. A 2017 review of amoebic meningitis notes that it “primarily occurs in previously healthy young males exposed to warm, recreational waters, predominantly in lakes, ponds, and reservoirs, in southern-tier states during the summer months.” (Whether males are somehow more susceptible or just more likely to be swimming in those areas is unclear.) It’s for this reason that natural hot springs often post a sign telling visitors not to submerge their heads in the water—that’s how the amoeba enters the nasal cavity.

That same review notes that, though more than 80 percent of the N. fowleri cases are from natural bodies of water, some have come from tap water. One 2013 case was traced to hose water used in a slip-n-slide, while a 2011 report from the same area came from using a neti pot. Tap water cases like this are generally because water becomes contaminated and then heated, often in pipes or hoses sitting above the ground that warm up in the summer sun and allow the amoebas to multiply rapidly. It can also happen in pools, though proper chlorination should kill off the organisms.

This is why you should always use sterilized water if you use any kind of sinus irrigation like a neti pot. You can swallow N. fowleri without risking infection, which means that safe drinking water may be very unsafe for your nostrils. If that water sits around or gets warm (many people heat the water so it’s not so cold going into the sinuses), it becomes a perfect home for N. fowleri. Fortunately, it’s easy to sterilize tap water: just boil it. But let it cool down before you blast it up your nose, of course!

It’s almost always fatal

The symptoms for amoebic meningitis look a lot like bacterial meningitis: headache, nausea, fever, and a stiff neck. If you show up to an emergency room with those symptoms, many doctors will assume that you have bacterial meningitis and will give you an antibiotic that’s unlikely to have any effect on N. fowleri. It’s only by interviewing you thoroughly that they might realize you have the amoebic variety, especially since symptoms may not come on for a week after you contracted the organism. Unfortunately, the Centers for Disease Control notes that amoebic meningitis usually progresses rapidly within 5 days, during which time the patient develops confusion, hallucinations, and seizures.

More than 95 percent of those who develop amoebic meningitis die, and just 27 percent of the cases even get diagnosed before the patient passes away. There are only a handful of people who have ever been known to survive it. It’s simply too rare for most physicians to be on the lookout for, and by the time they put the pieces together it’s usually too late. The treatment generally involves a combination of antifungals and antibiotics, along with drugs to combat the inflammation and procedures to drain cerebrospinal fluid (thus decreasing the pressure from brain swelling). Getting treated earlier seems to increase the odds of survival, so physician awareness of the disease could be crucial in identifying patients early enough for them to live.

It may be becoming more common

Prior to 2010, the northernmost case of amoebic meningitis in the U.S. was in Missouri. It is now as far north as Minnesota, as well as in states like Indiana and Kansas. In that 2017 review, the authors note that “with climate data showing consistently warming temperatures, the reports of PAM [or amoebic meningitis] cases outside of the southern-tier states is cause for concern,” continuing on to say that physicians in more northern areas should now be wary of N. fowleri. Climate change is going to warm up more of the world, and that means more people will live in places with waters friendly to N. fowleri—people who may not be aware of the dangers. Amoebic meningitis may be rare, but that doesn’t mean it can’t become more common. And knowing the signs could save your life.