NRP Fall 2023. Elyssa Pereyra: Yum… Brains!

Although one might think that brain-eating creatures are limited to the bounds of books or screens of movies, this is not the case. Brain-eating creatures are real. These organisms may not be the classic zombie one may think, but they similarly feast on human brains. They consist of a unicellular organism designed to intrude and consume the brain and are known as brain eating amoebas.

Brain-eating amoebas primarily reside in fresh water sources. A brain eating amoeba has the potential to be in two forms: a cystic form where amoebas are noninfectious and a pathogenic from where amoebas are infectious. Whether a brain-eating amoeba resides in the pathogenic state depends on the temperature of water. Once water temperatures rise above a certain level, brain eating amoebas will take a pathogenic form and can infect and consume an individual’s brain. Although brain-eating amoebas are not considered a public health risk, there has been an increase in brain-eating amoeba infections due to global rising water temperatures. Additionally, brain eating-amoeba infection has a low survival rate due to the rapid rate at which it can enter and consume a human brain.

 Entering a human brain is difficult to accomplish due to networks of barriers that serve as the brain’s protection. However, brain-eating amoebas use a unique entry point and have specialized cellular machinery that allows them to bypass these protective layers. They first enter an individual’s system through the forceful entry of water up the nasal cavity. Once these unicellular zombies enter the nasal cavity, they began their journey to the brain.  At the base of the noise, where the olfactory neurons involved in smelling lie, there is a structure called the cubiform plate. The cubiform plate consists of a highly porous bone resembling a wall with holes which can be used for points of entry.  Brain eating amoebas can pass through the cubiform plate by sliding through these holes.  After brain eating amoebas cross the cubiform plate, they still need to bypass the meninges which encase the entirety of the brain and serve to keep intruders out. To do this, brain eating amoebas will secrete metalloproteases. Metalloproteases are enzymes that effectively and efficiently degrade proteins. In the case of the brain eating amoeba, metalloproteases are used to degrade tight junctions, so they can slip past the meningeal layers and breach the brain.

Once brain eating amoebas arrive at the brain, their specialized cellular processes allow them to feast. Brain eating amoebas have lipolytic enzymes which break down the membrane of neurons. The degraded neuronal membrane is used as “food” to fuel amoeba replication leading to the presence of more unicellular zombies. They are also able break down myelin which is essential for fast and efficient signal transduction between neurons. They accomplish this using phospholipase which serves to break down the phospholipid membranes that compose myelin. Once myelin is lost, neurons fail to transmit signals at an effective rate. After infection, there will be rapid and systematic neuronal degeneration due to the consumption of neuronal membrane and loss of signal transduction which ultimately leads to the death of the infected individual.

Overall, the cellular mechanisms involved in intruding and consuming the brain demonstrate how microscopic organisms contain complex systems that can wreak havoc on our nervous system. Although brain-eating amoebas might not look like zombies, these lethal organisms still have the capability to feast on a human brain.