trophozoite

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Naeglaria fowleri, The brain eating amoeba

The term “brain-eating amoeba” makes the amoeba sound like a tiny zombie stalking your skull. But brains are accidental food for them.

There are many species of Naeglaria all over the planet which are present in warm soils and warm fresh standing water, however, only one species can infect humans. Like other amoebas, Naegleria reproduces by cell division. When conditions aren’t right, the amoebas become inactive cysts. When conditions are favorable, the cysts turn into trophozoites – the feeding form of the amoeba. After infection, it attacks the human nervous system and brain, causing deadly primary amoebic meningoencephalitis (PAM)

Naeglaria fowleri was discovered in 1965. Since this date, only around 144 cases have been officially documented worldwide. At only 8 micrometers to 15 micrometers in size, depending on its life stage and environment (roughly 1/3 the diameter of a human hair), it’s hard to believe that infection by this amoeba has a 95% mortality rate. Even though infection is relatively rare, mortality is extremely high. There is no vaccine or standard treatment method.

 How do you catch it?!

The parasite exists in very warm standing water and sediment, so many people have caught the parasite from swimming or doing water sports in water that contains it, e.g. lakes and swimming holes. A whole glass of Naegleria water can be swallowed without incident, as your stomach acids make short work of burning them up. However, when people jump or fall into water, the pressure can force water (and therefore the parasite) up the nasal passages of the nose. This gives Naegleria easy access to the olfactory nerves in the nose and a quick route to the brain.

It eats brains?!

Yep. Braaaaains. In the first big gif above, you’re looking at Naegleria fowleri consuming human nerve cells. When the parasite has access to a host’s nerve and brain tissue it’s in its ideal habitat- somewhere warm and safe with lots of food. Studies suggest that N. fowleri amoebas are attracted to the chemicals that nerve cells use to communicate with one another. Once infected, the parasite moves its way into the brain where it multiplies and starts feasting. It is only usually discovered days after infection- when tissue damage starts to cause symptoms (and it’s too late).

In the second gif above, you can see a Naegleria fowleri amoeba destroying a cell. The organism begins to consume cells of the brain,piece by piece, by means of an amoebostome, a unique actin-rich, sucking apparatus extended from its cell surface. It attaches itself to the cell surface and chemically makes a cut in the cell wall. When the contents of the cell spills forth the parasite consumes them by breaking them down with enzymes that dissolve protein. It eventually causes necrosis (tissue death) and haemorrhaging. 

In response to this, the body sends out its A-team, the white blood cells, to deal with the attack. As you can see in the second gif, the white blood cells attempt to attack the Naeglaria fowleri organism, but are thwarted. The amoeba grows a ‘coating’ that the white blood cells cannot adhere to so they cannot attack it, which it then discards and uses to escape. The immune system goes into overdrive at this point and causes inflammation and swelling of the brain. 

Despite such a large mortality rate, studies show that many people may have antibodies to N. fowleri. That suggests that they became infected with the amoeba but that their immune systems fought it off.

So what are the symptoms?! 

Symptoms include: Problems with taste and smell, headache, fever, stiff neck, loss of appetite, vomiting, altered mental state, coma and seizures. It takes two to 15 days for symptoms to appear after N. fowleri amoebas enter the nose. Death usually occurs three to seven days after symptoms appear. The average time to death is 5.3 days from symptom onset. Only a handful of patients worldwide have been reported to have survived an infection.

How can I NOT catch N. fowleri?!

Firstly, be really careful when swimming in fresh standing water during warm weather when N. fowleri loves to multiply. Also, if you’re swimming or doing water sports, you can wear nose plugs and make sure you don’t swallow any water. When drinking water from lakes, or performing nasal irrigation (yes…I know), always use boiled or distilled water. Boiling water kills off the parasite. If you own a pool, make sure that it is chlorinated and if you drink water make sure that it is treated. 

It’s VERY RARE to be infected by N. fowleri and develop PAM. Nonetheless, not allowing this remarkable little creature access to your brain is the first step to not having it eaten.

Another thing to think about…. N. fowleri LOVES warm water. As temperatures rise, more cases could be seen in more temperate areas that are less favourable to its growth. Be careful with any standing water (wherever you are) in warm weather.

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