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Brain-eating amoeba? What is an amoeba/ameba anyway?

August 18, 2011|By Rosie Mestel, Los Angeles Times / For the Booster Shots blog
  • Brain tissue infected by the amoeba Naegleria fowleri, which lives in lakes and ponds. It has recently killed several people in the U.S.
Brain tissue infected by the amoeba Naegleria fowleri, which lives in lakes… (CDC )

The recent brain-eating amoeba deaths in Florida, Louisiana and Virginia may have some people wondering something they haven't given a thought to since the last basic bio class: What is an amoeba anyway? 

Well, it just so happens that in cleaning out my garage the other day I unearthed my 1978 college notes from a class called “Fundamentals of Biological Organization,” and as luck would have it, they contained a rendition of an amoeba, below.

OK, so it’s not very good.

Notes accompanying the drawing explained that amoebae are single-celled creatures that move around by extending bits of themselves in arm-like structures called pseudopodia (“false feet”). The inner goo of the cell streams into the arm, making it longer and longer. Then the rest of the blob sort of catches up with the arm. In this manner, the amoeba makes glacial progress in the direction it “desires” to move in (say, sludging along on the bottom of a pond or lake).

More amoeba facts:

They’re hard to treat with drugs, because they’re far more similar to human cells in structure and inner workings than bacteria are.

The brain-killing amoeba in the news, Naegleria fowleri, was named after Australian pathologist Malcolm Fowler, who was the first to isolate it, back in the 1960s, from a patient who had primary amoebic meningoencephalitis, as the severe brain infection caused by the creature is called. It’s a freshwater-dwelling amoeba that makes its way into the body up the olfactory nerve when splashed in the nose, and thence to the brain.

Infections like this are extremely rare: A book at the National Institutes of Health website noted about 175 reported cases worldwide of primary amebic meningoencephalitis as of 1995. (Depending on where you look, the spelling is "ameba" or "amoeba.")

“It is clear that the number of infections represents only a minute fraction of the number of exposures,” the book says. In other words, lots of people are exposed to the creature but never get sick.

Several species of another group of amoebae, Acanthamoeba, cause skin and lung infections in people with compromised immune systems, and can spread to the brain. In healthy people, they can cause Acanthamoeba keratitis, a rare but serious eye infection, in cases of poorly cleaned contact lenses.

Then there’s Entamoeba histolytica, which can inhabit the large intestine without causing harm but according to MedlinePlus, sometimes, it invades the colon wall, causing colitis, acute dysentery or long-term (chronic) diarrhea. The infection can also spread through the blood to the liver and, rarely, to the lungs, brain or other organs.”  

There are other amoebae we can ingest from sewage-contaminated water, such as one called Entamoeba coli, and though these are not harmful they do indicate that someone’s been exposed to sewage, much as otherwise harmless coliform bacteria do.

Other amoeba facts:

Unlike bacteria, amoebae don’t have any hard wall around them, and as a consequence they would burst from an inflow of water if it weren’t for a “contractile vacuole ” –- see it there in that old bio class picture? -- that steadily pumps water out of them.

Some amoebae are “social”; “social amoeba” is an actual biological term. That includes the slime molds, which aggregate together to form sort of amoeba communities.

Amoebae aren’t the only cells that move like amoebae: Our white blood cells do it also, for example.

Much, much more about amoebae at this educational website.

Still not sated? Here’s an amoeba PowerPoint presentation.

Finally, here is an Animal Planet video of Naegleria fowleri in action.

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