By: Sheli Tonkonogi
“16-year-old becomes fourth known person to survive brain amoeba in 50 years”. “Florida 13- year-old battles brain-eating amoeba after beach trip”. “Brain-Eating Amoeba In Water Causes Texas Boy’s Death”.
The brain-eating amoeba, also called naegleria fowleri (its scientific name) and the disease it causes, primary amoebic meningoencephalitis, will often make the headlines of the news. But why exactly is this parasite so dangerous? Is there any way to prevent infection, or reduce the risk? Before answering these questions, it is first important to understand what exactly this amoeba is, and how it infects us.
An amoeba is a microbe with a nucleus, the centre that contains all of its genetic information. It hunts bacteria and other critters, which it will usually devour whole and rip into pieces. Like many amoebae, it is able to transform into different stages in order to help it survive. These stages are the cyst stage, the trophozoite stage and the flagellated stage. Generally, it is found in its trophozoite stage; during which, it looks like a blob with arms and will hunt, divide and thrive.
This amoeba lives in freshwater: ponds, rivers, lakes and hot springs. However, it can also survive in pipes, swimming pools, fountains and spas if they are not treated properly. The warmer the water, the more it is able to thrive and multiply. This is why if humans are infected, it is often in the warmer, summer months when many of them go to pools, rivers, and lakes in order to cool off. If you are going swimming, it can be difficult to completely avoid the amoeba and many people have contact with them but that is okay. Many actually have antibodies against it, and you could even swallow water contaminated with it without consequences. Things take a turn for the worse when people dive or swim in water that is contaminated with it and water gets high up their nose. Let’s take a look at what happens when this horrifying parasite infects you.
When the amoeba first enters your nose, it isn’t really looking for trouble, it only wants to eat some bacteria. The amoeba is approached by your natural defenses, but it is actually very good at avoiding detection by your immune system. Your nose is filled with a slime known as mucosa, filled with chemicals that help to stun or kill possible invaders or alert immune cells. However, this does not affect naegleria fowleri. As it continues its journey, it may stumble over something that piques its interest: nerve cells. Your nose is filled with a network of olfactory nerve cells. These cells will pick up information from outside and send the information to your olfactory bulb, the brain’s smell centre. The cells communicate with each other through the use of various messenger chemicals, which are then recognized by specific receptors. One of the most important chemicals used is acetylcholine. Naegleria fowleri has receptors that recognize acetylcholine and it seems to attract it almost irresistibly. So as your cells continue to use acetylcholine to talk to the brain, naegleria fowleri enters your tissue.
Neutrophils, a type of immune cell, will begin to attack the amoebae; but on their own, they are not very effective at stopping them as the invaders are large and well equipped fighters that are used to dealing with difficult enemies. So, the neutrophils swarm the amoebea, killing them either by vomiting chemicals on them that punch holes in them or ripping pieces off of them and devouring them whole. While the neutrophils slow down the invaders, the naegleria fowleri continues their journey to their final destination: your brain.
This process can take anywhere between 1 and 9 days and during this time, you will likely not feel anything, until the amoebae reach the olfactory bulb, which is the entrance to the brain. At this point, the naegleria fowleri will release various attack molecules, some of which act a little like bombs, creating holes in the cells found in the brain so that they can be consumed. The naegleria fowleri will multiply and in a feeding frenzy can develop as many as 12 feeding cups, which resemble large and creepy looking mouths. The amoebae will engage brain cells, suck them in and then tear off large bites while they are still alive.
From this point forward, everything escalates quickly and the disease becomes terminal. Alerted by the massacre caused by this amoeba, millions of immune cells (eosinophils, microglias and neutrophils) rush to the infected tissue. Unfortunately, your immune system is not a very careful fighter. It is similar to burning down an entire forest just to kill a certain kind of pest - which is not a very good idea when it comes to the brain. Your immune cells will begin to fight the amoeba using every weapon available to them from trying to eat them alive to using chemicals. Neutrophils explode themselves, erecting barriers spiked with deadly chemicals.
Naegleria fowleri is actually capable of fighting back and will attack and kill many immune cells. The immune system uses all of its remaining resources to fight the enemy, but this is all in vain. The complement system, tiny protein bombs that can kill intruders are easily diabled and antibodies, which are usually incredibly effective, are either destroyed or swallowed. A high fever that usually helps slow down invaders is ineffective as the naegleria fowleri is actually a thermophile, meaning that it thrives in the heat.
A catastrophic chain reaction is taking place. When your immune cells fight, they cause inflammation, directing large amounts of fluid from your bloodstream to the site of the infection. As the battle continues, more and more fluid is directed into the brain. The infected human will start to feel symptoms that quickly escalate at this point. They begin rather vaguely with a headache, fever and nausea but later progress to symptoms such as confusion, inability to concentrate, seizures, fatigue and hallucinations. The brain swells but can’t expand due to the surrounding bones, causing it to compress and disable the brainstem which controls functions such as breathing. The patient is usually dead within a week.
This fate is shared by about 97 % of patients infected with this amoeba. In most cases, by the time the infection is recognized, there is very little that can be done. Additionally, we currently don’t have any effective treatments for primary amebic meningoencephalitis. This amoeba continues to baffle scientists and there are still numerous unanswered questions about its ability to masterfully evade the body’s defenses, especially when it is used to living in water.
So how common is this amoeba exactly? Or in other words: how worried do you need to be? The answer is not very. Infection is very rare and it is more likely that you will drown in a swimming pool than be infected. Additionally, the amoeba must get high up your nose and make it past your initial defences. So, how can you reduce your risk? Don’t swim in or jump into warm freshwater lakes (particularly if there have been cases where people were infected) and hold your nose shut or use nose clips when jumping into or swimming in warm freshwater.
We still have a lot to learn about this deadly parasite and while this may be scary it is also exciting as it means that there are still many opportunities in the future to continue building on to what we do know. It means that perhaps one day, we will find a cure.
References:
The most horrible parasite: Brain eating amoeba. YouTube. (2022, May 3). Retrieved August 14, 2022, from https://youtu.be/7OPg-ksxZ4Y
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