Beware of the brain eating amoeba -Naegleria fowleri

Maria Allera (11 AM Micro) is worried about parasitic diseases, and with good reason. She found a news alert about the brain eating amoeba, which has long been one of my favorites. Who can forget this classic episode of House which featured Nagleria, and was one of the last times I got to trot out the #BOGUS hashtag? Let’s see if Maria can make us feel better about Nagleria:

Naegleria fowleri is an amoeba that takes residence in warm, fresh water all over the world. Just two weeks ago N. fowleri turned up in a water supply in Louisiana, causing the town to go into a state of emergency to provide bottled water for all the residents. N. fowleri can be found in any body of water, such as lakes, ponds, rivers and even manmade structures like pools or waterparks. The amoeba thrives in hot water and can also be found in water discharges from industrial plants.

When N. fowleri comes in contact with a human it makes its way into the body through the nasal passage, swims to the brain and causes an often fatal infection called Primary Amebic Meningoencephalistis (PAM). Some symptoms of PAM include headaches, fever, nausea, vomiting, hallucinations and coma; all of these can lead to death. Since the 1960’s only 200 conditions have been reported, unfortunately less than 5% survive. The infection can be diagnosed when examining spinal fluid under a microscope to identify the amoeba. Under the microscope the amoeba appears as:

Naegleria fowler is elongated, 15-30 μm, and feeds on Gram-negative bacteria. The cytoplasm is granular, has a single nucleus with a prominent and contains vacuoles. Blunt lobular pseudopodia are formed at the widest point. The flagellated form is smaller, with a pear shape and two flagellae at the broad end. N. fowleri cysts are round, 7-15 μm in diameter and have a thick smooth double wall. N. fowleri is thermophilic, preferring water temperatures between 35 and 46ºC (link here)

Within the amoebas life there are three stages. The first two stages, the cyst and flagellate stage, require low food supply and low temperature. When an amoeba is in the cyst or flagellate stage it cannot survive in human tissue. The human body is the perfect living condition for the trophozoite stage. The amoeba feeds off of the human blood cells, it reproduces by binary fission and destroys other tissues. As dangerous as this microorganism sounds, it all depends how it is ingested to determine if it will cause harm or not. If you consume water with N. fowleri in it, it will process through your digestive system without any health problems. This amoeba is only dangerous when it gains nasal access.

Naegleria fowleri in its trophozoite stage, from the CDC

Just like any pathogenic disease everyone wants to know how to prevent acquiring it and how to treat it if acquired. To prevent contracting N. fowleri, it is smart to not submerge your head in fresh water, especially if it is a warm temperature. Try to always swim in treated waters and don’t wash your nose out with fresh water. Do not use a neti pot to clean your sinuses, the water goes straight up the nose so if the water is effected you’re putting your body directly at risk. Unfortunately most infections of N. fowleri end in death, there are a few survival stories. There have been four survival cases in North America, a laboratory did testing and the CDC released

It has been suggested that the original U.S. survivor’s strain of Naegleria fowleri was less virulent, which contributed to the patient’s recovery. In laboratory experiments, the original U.S. survivor’s strain did not cause damage to cells as rapidly as other strains, suggesting that it is less virulent than strains recovered from other fatal infections.

Amphotericin B  was the most common medicine to treat amoebas. It’s inserted directly into the brain; however, this treatment usually fails. The CDC also has an investigational drug on study called Miltefosine for three free living amoebas including N. fowleri and it has had much better results.

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About ycpmicro

My name is David Singleton, and I am an Associate Professor of Microbiology at York College of Pennsylvania. My main course is BIO230, a course taken by allied-health students at YCP. Views on this site are my own.

Posted on September 21, 2014, in Danger danger danger!, Guest Post. Bookmark the permalink. 6 Comments.

  1. As somebody who prefers warm bodies of water over cold ones, this article will definitely make me think twice about putting my head in the water. It’s somewhat scary to think about how it can live in so many environments, unbeknownst to people.

  2. I always wanted to get the ear of an infectious disease doc. I think back in 7th grade we learned that amoebae would revert from the third stage to the first stage if subjected to cold temperatures. If memory serves, the last US survivor was placed in a hypothermic induced coma. It would slow the amoebae down and then give the fungicidals more time to work… I hear they were looking into clorpromazine as a treatment. That ever pan out?

    • Tom–thanks for commenting! There were actually two US survivors in 2013, which was actually very surprising. Both patients were diagnosed early, which was likely critical, and both also received miltefosine as an experimental treatment. Miltefosine is used in the treatment of several other protozoan diseases (leishmaniasis, schistosomiasis), however has not been indicated for this use previously. Other than those two cases a year ago, there have only been two other case studies in the literature describing survival of primary amoebic encephalitis. One of them was on an episode of House.

  3. Thomas C. Barnes

    I’ve found my way back to this site and I am really impressed with your articles, Dave. Your writings have a rare balance of scholarship and accessibility… Keep ’em coming!

    I had come across another article about miltefosine being used for these 2 cases and, if I recall correctly, the author opined that treatment latency was a significant factor for predicting outcomes. The female patient started within 36 hours of symtom onset and made a full recovery; in contrast, the male survivor started the treatment a few days after onset and he will likely experience permanent CNS damage. I noted at the time that there was another variable – medically induced hypothermia. Female got it, male did not. (Of course, I think the treatment team was viewing the hypothermia as means to reduce intercranial pressure from the inflammation and NOT to regress the amoebae to their “dormant” state.) I was just wondering aloud whether cooling the host had that ancillary benefit. Definitely out of my league here, but I’ll be visiting far more frequently! I may start something similar for cognitive/biological psychology. Lots of things need debunking in my field too!

    • Hi Tom, thanks a lot for the kind words! I started this up just about 4 years ago, initially as a personal writing exercise, plus as a mechanism to drive student engagement in the Nursing Micro course. I’m always happy to see people clicking in from FB or Twitter, that actually requires a conscious effort to click the link. For the students in my class, they are kind of a captive audience as I embed the WordPress blog into our college’s Learning Management System–the course site has this stuck in the middle. Currently, I am not getting to personally update as frequently as I do other times in the semester. There is a lot of interest in guest posting, like Maria above, with the enticement of bonus points. Fortunately, the students who take the time to find something find interesting topics to present!

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