Acanthamoeba,
A Short Study in its Pathogenicity

 
Text copyright Ken Ramos, 2004. All rights reserved.
 
 
 
 
 

For those of you who have read my previous article, "Beware the Ides of Summer", you have no doubt come to the conclusion that I am keenly interested in the hazards associated with amoeba that pose the potential for serious infections in human beings.

Most often we associate amoeba with aquatic environments such as lakes, ponds, streams, and rivers. Seldom do we give thought to the soil, the dust which we undoubtedly breath, hot tubs and spas, swimming pools, tap water or drinking water, dialysis units, heating, venting, and air conditioner units (HVAC), humidifiers, contact lens paraphernalia, or even our own nose, throat, and mouth. All of these carry amoeba and, in some, the amoeba may even host bacteria that can cause life-threatening illnesses. Following in the steps of one Mynheer Antonie van Leeuwenhoek, whose letters to the Royal Society in London some of us have read, I have isolated and observed amoeba from my own person.

So what about this Acanthamoeba spp. which I have referenced in my title? Acanthamoeba poses a threat similar to that of the amoeba Naegleria fowleri, the causative agent of Primary Amebic Meningoencephalitis or PAM, and can be found in all the referenced environments previously given. But what's the big deal about these pathogens? We all know that infections are rare and most always fatal. Well, there is no big deal about them but they are part of our environment and, as microscopists, something that we should be aware of. There have been no reported cases of anyone having self-infected themselves with the amoeba but, according to "Murphy's Law", there is always that slim chance one day that someone could, and probably will, infect themselves. Now that may not be a very professional or scientific statement but it does hold a significant amount of weight. We handle our collections of protozoa cultures in a casual way for the most part, I am assuming, and I too am guilty of the same. However, it is always in the back of my mind that I am handling a potential biohazard and should be taking some precautions, however menial they may be. Although we may harbor these organisms in our bodies, all it takes is just one of them in the right place at the right time and you could have a serious and fatal infection up and running. The dropping or splashing around of water sample collections containing these and other organism like them pose a threat, however small and rare that threat may be. From such carelessness, microscopic droplets or mists can transfer these organisms to the air we breathe. Our hands are another potential source of infection. By rubbing ones eyes, eating or drinking, even smoking if you are so inclined to do so, without washing ones hands after handling or preparing wet mount slides or even collecting samples, one can possibly transfer these organisms to one's person.

There are many other infections and diseases that are caused by amoeba and not all of them are fatal but are serious enough, for those infected with them, to have to acquire medical attention.

O.K. so now I am an alarmist, a "Chicken Little", if you please. Well here are the facts about Acanthamoeba and they are not pleasing ones.

The environments in which these amoebae live and thrive have already been addressed. Like N. fowleri, they are thermophilic, capable of living in environments that have extremely warm or, sometimes, hot temperatures. The result of an Acanthamoeba infection is the same as that for N. fowleri but the course of the infection leading to the final end result, death, takes a much longer route. This route can progress over several weeks.

How does one acquire an Acanthamoeba infection? Some of that has already been addressed, too, but here are some more interesting facts concerning acquisition. The amoeba can enter the skin through a cut, wound, or through the nostrils. Having invaded the body, the amoeba can travel to the lungs and through the bloodstream to other parts of the body, especially the CNS or Central Nervous System. Also, through improper handling and disinfection of contact lenses, one can cause a serious infection of the eye known as amebic keratitis (AK). Once inside the CNS the symptoms of Granulomatous Amebic Encephalitis or GAE are pretty much the same as for Primary Amebic Meningoencephalitis, PAM. They are as follows:

  • Headaches and a stiff neck.
  • Nausea and vomiting.
  • Tiredness and confusion.
  • Lack of attention to people and surroundings.
  • Loss of balance and bodily control.
  • Seizures and hallucinations.

As for treatment, yes skin and eye infections can be treated. As for the infection of the CNS, Amphotericin B is most commonly used. Now, have there been any survivors of an Acanthamoeba infection of the CNS? The answer to that is yes but only five (5) out of about 300 cases worldwide.

I do not want to make this a long and drawn out report but here are a few more facts about Acanthamoeba spp. that some may be interested in. Acanthamoeba are not parasites. They are free-living amoeba and do not require a host organism to complete their life cycle, hence the term free-living. There are several species of Acanthamoeba and they are as follows:

  • A. culbertsoni
  • A. polyphaga
  • A. castellanii
  • A. healyi (A. astronyxis)
  • A. hatchetti
  • A. rhysodes

and possibly others.

The main causative agent species of Acanthamoeba are: A. polyphaga, A. castellanii, and A. culbertsoni.

Acanthamoeba can be easily isolated and cultured on non-nutrient agar cultures covered with a dense layer of the bacterium, Escherichia coli. The trophozoites will feed and replicate on the bacterial food supply or source. With experience one can identify Acanthamoeba from other free-living amoeba using microscope slide preparations and observing the morphology of the amoeba.

I hope that you the reader, have found this short article to be interesting as well as informative and that some of the information about the hazards handling these organisms will be taken to heart. With things being the way that they are these days, I must add a disclaimer to my article: I am not a professional but an amateur researcher in the field of Protozoology and the study of pathogenic protozoa. Misuse of the information contained herein is at the risk of the individual reader or readers and I claim no responsibility or liability for its misuse and that it is written for informational purposes only and that my opinions and findings are that of an amateur and not a professional. For more information on this and other pathogens of this nature, please contact the Center for Disease Control, www.cdc.gov or consult your local offices of health. If you think that you have been exposed or infected with any of the organisms listed and would like further information contact your physician at once.

References:

Center for Disease Control, Division of Parasitic Diseases, Reviewed March 2001, www.cdc.gov

AwwaRF, Drinking Water Inspectorate Fact Sheet--Acanthamoeba, Fact Sheet No. 11: Issue No. 1 March 1997 ©Crown Copyright 1996 www.awwarf.com

Text copyright Ken Ramos, 2004. All rights reserved.

About the Author

Ken Ramos is a retired U.S. Navy, Petty Officer. He now calls Western North Carolina home, the city of Rutherfordton, after 21 yrs. of naval service. Although his new home has not a "flight deck" or aircraft landing overhead while he is trying to sleep, he is coping fine. His interests lie in the study of Nature and Microorganisms, chiefly Protozoa and as an amateur, is currently researching infectious diseases associated with Protozoa. Leisure activities include fly tying and fly fishing for trout in the mountain streams of Western North Carolina and wilderness hiking.

 
 
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