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Acanthamoeba Facts, Eye Infection, and Keratitis

Linda Crampton is a writer and teacher with a first-class honors degree in biology. She often writes about the scientific basis of disease.

An Acanthamoeba trophozoite viewed under a phase contrast microscope

An Acanthamoeba trophozoite viewed under a phase contrast microscope

What Is Acanthamoeba?

Acanthamoeba is a microscopic, single-celled organism that is found in the environment and sometimes becomes a parasite in humans. It can cause a disease called Acanthamoeba keratitis in the eye. In this often painful condition, the patient's cornea becomes cloudy and the person finds it difficult to see. If the disorder isn't treated, permanent vision problems or even blindness can result. Contact lens wearers are especially susceptible to the disease. The disorder is rare, but recently there have been increased reports of people suffering from the condition.

Many species of Acanthamoeba exist and multiple forms infect humans. The different species are often hard to tell apart visually, but scientists can identify them genetically. They have a widespread distribution and some interesting features. The organisms sometimes live in our body without making us sick. Unfortunately, they can also cause disease.

The CDC (Centers for Disease Control and Prevention) lists nine species of Acanthamoeba that can infect humans. The species are often referred to as a single entity, but researchers have found differences between them.

The eye as seen through a healthy and transparent cornea

The eye as seen through a healthy and transparent cornea

Distribution in the Environment

Acanthamoeba species are very common in the environment. The list of places where they've been found is alarmingly long. The amoebas are found in soil, on plants, and in fresh water. They can be found in tap water, swimming pools—even chlorinated ones— lakes, rivers, and ponds. They have also been found in sea water and in the air. They've been discovered in and on items and equipment that we use, including bottles of mineral water and distilled water, vegetables, shower heads, heating and air-conditioning devices and ducts, hospital equipment, sewage, and contact Iens cases.

It's thought that most of us are exposed to the organism on a routine basis and that it frequently enters our body. In most cases, this doesn't make us sick. Another interesting observation is that although the incidence of Acanthamoeba keratitis is highest in contact lens users, many people who wear the lenses don't develop a corneal infection. In addition, when the cornea is infected, the infection is prevented from travelling further into the body.

The observations described above suggest that our bodies have very effective ways to protect us from the parasite, or at least from most varieties of the parasite and under most conditions. Researchers are trying to discover exactly how this protection works.

Acanthamoeba Cells

Like other amoebas, Acanthamoeba is frequently referred to as a protozoan. Amoeboid protozoans move by extending part of their body and then slowly flowing into it. The extension from their body is known as a pseudopod. Pseudopods, or pseudopodia, are extended in different directions as the organism moves. This behaviour may remind some people of the amoebas that they observed in school. The word "amoeba" is sometimes used as a general term for all organisms that move by extending pseudopods.

Acanthamoeba feeds on bacteria, yeasts, and organic particles. It extends pseudopods around its prey to trap it. The prey then enters a food vacuole, where digestion occurs. The amoeba also extends fine, spine-like pseudopods from its body, which are often called acanthopodia. They can be seen in the first photo in this article and in the video above.

The nucleus of the parasite is spherical and contains a nucleolus in its centre. The cell has one or more contractile vacuoles. These absorb water that enters the cell and then release it through a temporary pore in the cell membrane.

There are two stages in Acanthamoeba's life cycle: the trophozoite and the cyst. The trophozoite is the amoeboid stage and the one that feeds. The cyst is a double-walled stage that is inactive. It forms when conditions are potentially dangerous for the cell. Examples of these conditions include lack of food, a change in pH, temperature extremes, and the presence of harmful chemicals.

Giant viruses have been found in some types of Acanthamoeba. Giant viruses are huge compared to their smaller relatives and have some distinct features.

Structure of the eye and the cornea

Structure of the eye and the cornea

Structure and Function of the Cornea

The cornea is the outermost, transparent layer at the front of the eye. Light rays reflected off objects pass through the cornea and then travel to the retina at the back of the eyeball. The retina sends a signal along the optic nerve to the brain, which creates an image. If the cornea becomes cloudy and no longer transmits light rays to the retina, we will be unable to see.

The cornea consists of five layers. Starting at the front of the eye, these layers are as follows:

  • epithelium - a surface layer that is five to seven cells thick and protects the cornea
  • Bowman's layer - a thin layer made of collagen, a major protein in our body
  • stroma - the thickest part of the cornea; contains collagen fibres and cells called keratocytes
  • Descemet's membrane - a thin layer made of collagen fibres that are in a different form from those of the stroma
  • endothelium - the thin, innermost layer

The collagen fibres in the cornea have a specific arrangement. This arrangement is vital in order to maintain the transparency of the cornea. If the alignment of the fibres and the spaces between them are changed, the cornea becomes cloudy.

Possible Causes of Acanthamoeba Keratitis

Keratitis is inflammation of the cornea. An Acanthamoeba infection is one cause of the problem, though other microbes can also cause keratitis. The infection may develop due to one of the following factors.

  • Washing the hands but not completely drying them before touching contact lenses (Water drops on the hands may contain the parasite.)
  • Cleaning lenses incorrectly by using tap water or a homemade solution
  • Wearing the lenses while showering, swimming, using a hot tub, or participating in any other activity that may expose the eyes to contaminated water
  • Storing the lenses in an unsterile environment
  • Experiencing repeated trauma to the cornea (Wounds on the cornea make it easier for the parasite to enter.)

Photo A above shows the cornea of a patient with Acanthamoeba keratitis. Photo B shows the cornea of a patient after sodium fluorescein administration. The chemical is used as a diagnostic tool.

Effects of the Parasite

The actions of the parasite and the ways in which it exerts its effects are still being studied. The basic steps of the infection are described below.

  • The parasite adheres to the surface of the cornea.
  • It then breaks down the outer layer of the cornea, or the epithelium.
  • Next, it enters the cornea.
  • Once inside the cornea, the parasite begins to destroy it. The destruction involves the loss of the stroma (which forms the bulk of the cornea), including the keratocytes. These cells make the materials in the cornea and repair the structure when it's damaged or inflamed.

Acanthamoeba cysts may form within the stroma. These sometimes survive the treatment for the disease, releasing new trophozoites afterwards. This is one reason why the disorder can sometimes be hard to treat.

Possible Symptoms and Treatment

Some possible symptoms of Acanthamoeba keratitis are listed below. A patient may not have all of them. In addition, the symptoms may indicate the existence of a different problem.

  • eye pain, which may be severe
  • red eyes
  • a feeling that something is in the eyes
  • blurred vision
  • an excessive production of tears
  • light sensitivity

The infection is generally treated with antimicrobial chemicals that kill the parasite. Current medications sometimes take a considerable time to work, however, because the parasite is becoming resistant to certain drugs. If the cornea becomes seriously scarred, a corneal transplant may be needed.

Acanthamoeba cysts in interference contrast microscopy

Acanthamoeba cysts in interference contrast microscopy

The black scale bar in the photo above and in the first photo in this article represents ten micrometres. A micrometre is one thousandth of a millimetre and a millionth of a metre.

Preventing the Disease

The following steps are often recommended to prevent the development of Acanthamoeba keratitis.

  • Wash and dry hands before touching contact lenses.
  • Don't allow tap or other drinking water to contact the lenses.
  • Remove the lenses in potentially harmful situations, such as showering.
  • Clean the lenses with sterile solution recommended by an eye doctor.
  • Follow the instructions about using the sterile solution carefully.
  • Store the lenses in their case.
  • Follow the instructions about cleaning the case and replacing it.
  • Visit the eye doctor regularly so that any problems can be discovered in an early stage when they may be easier to treat.

Acanthamoeba keratitis is a rare infection, but when it occurs, it has a devastating effect for a long period of time on the patient's life. Only 70% of patients were cured within 12 months. For the remaining 30%, the treatment took over a year."

— Dr. John Dart, Moorfields Eye Hospital, via CNN.

An Outbreak of Acanthamoeba Keratitis

The incidence of Acanthamoeba keratitis tripled between 2011 and 2016 in southeast England. The outbreak appears to be continuing. Researchers from University College London and Moorfields Eye Hospital have been studying the situation. After analyzing data from questionnaires, they say the reasons for the outbreak are likely one or more of the following:

  • poor lens hygiene
  • the use of a lens disinfectant containing a chemical called Oxipol (which is no longer used by the manufacturer)
  • wearing contact lenses while swimming or in a hot tub

Acanthamoeba is more common in the UK water supply than in that of many other countries. This is due to the fact that the water often comes from a domestic supply instead of a major one. The water in local areas is frequently rich in lime, which supports the growth of the parasite population. Despite this fact, other countries are following the UK outbreak with interest because similar events have occurred in additional parts of the world, including the United States.

Moorfields Eye Hospital says that they have only seen cases where both eyes have been infected by Acanthamoeba at the same time instead of ones in which the parasite has spread from one eye to another. It's possible to have the infection in only one eye, however.

Further Studies About an Interesting Organism

Biologically, Acanthamoeba is an interesting organism. From a medical point of view, it's important to learn as much about it as possible. Further studies are needed to clarify its behaviour in our body and the way in which the body responds to its presence. We need to know how the different species and strains of the parasite behave, how people resist the infection, and how to prevent it in susceptible people. The results of the research could be very interesting as well as helpful.

References

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2018 Linda Crampton

Comments

Linda Crampton (author) from British Columbia, Canada on April 12, 2020:

Thanks for the visit, Denise. It's probably important to be important when dealing with the eyes, especially at this time. Best wishes to you.

Denise McGill from Fresno CA on April 12, 2020:

Okay, I'm scared now. I don't always dry my hands before putting my lenses on in the morning. I've never had any problems but then I don't want any either.

Blessings,

Denise

Linda Crampton (author) from British Columbia, Canada on March 08, 2020:

Hi, Peggy. Thanks for the visit. Keeping contacts clean is very important.

Peggy Woods from Houston, Texas on March 08, 2020:

I have never been tempted to wear contacts after I had to start wearing glasses. It is good that you are publicizing possible problems with this Acanthamoeba possibility of infecting the cornea if contacts are not kept scrupulously clean.

Linda Crampton (author) from British Columbia, Canada on February 27, 2019:

Thanks for the visit and the comment, Peg. “Creepy” is a good way to describe Acanthamoeba!

Peg Cole from Northeast of Dallas, Texas on February 27, 2019:

Interesting to find out that tap water can be contaminated with this parasite. Yikes. Creepy little critter, this one is. Luckily, I don't use contact lenses anymore but I will stop opening my eyes when washing my face now.

Linda Crampton (author) from British Columbia, Canada on October 22, 2018:

"Yuk" is a good word to describe the problem! The disease is still classified as rare overall, but the outbreaks are worrying.

Ethel Smith from Kingston-Upon-Hull on October 22, 2018:

Oh Yuk. And worrying that it is so bad in the U.K.

Linda Crampton (author) from British Columbia, Canada on October 02, 2018:

Thank you very much, Mel. Microbes can certainly cause serious effects. They're interesting to study, though.

Mel Carriere from San Diego California on October 01, 2018:

One more thing to worry about. Forget about the six legged and four legged disease causing pests, these tiny little critters with the pseudopods are the real killers. Brilliantly researched and extremely informative, as usual.

Linda Crampton (author) from British Columbia, Canada on September 30, 2018:

Thank you for the visit and the comment, Dora. I hope the week ahead is a good one for you.

Dora Weithers from The Caribbean on September 30, 2018:

Thanks for the information, and the warning about this disease. So happy to know that "our bodies have very effective ways to protect us from the parasite." You also give helpful suggestions on treating our eyes with care.

Linda Crampton (author) from British Columbia, Canada on September 29, 2018:

It's a shame you couldn't keep wearing the contacts. Having the vision of a young person sounds great to me! It does save you the trouble of keeping the lenses clean, though. Thanks for the visit, Roberta.

RTalloni on September 29, 2018:

So, okay, now I feel better that I can no longer wear contacts. The bifocal ones were like having 20 year old eyes but steroids created a problem...long story... However, it really is amazing that we aren't all suffering from this little bug's ability to wreak havoc. Thanks for the prevention tips.

Linda Crampton (author) from British Columbia, Canada on September 29, 2018:

Hi, Jackie. I would think carefully before getting contact lenses, too. I know that many people wear them with no problems, but buyers must be committed to following lens hygiene procedures.

Jackie Lynnley from the beautiful south on September 29, 2018:

I have lately been contemplating contact lenses. I think this will make me think twice being a vain plan to change eye color. Even if rare, it seems I am one of those people allergic to everything so I might just be one to contract this.

Horrible stuff, thank you for informing us.

Linda Crampton (author) from British Columbia, Canada on September 29, 2018:

Hi, Devika. Yes, proper care of contact lenses is very important in order to prevent infections.

DDE on September 29, 2018:

Most helpful about using contact lenses. The important points most individuals ignore and you shared it all here. Proper care is always acquired when using lenses the eyes are delicate and infections can easily arise.

Linda Crampton (author) from British Columbia, Canada on September 27, 2018:

Hi, Bede. Thank you for commenting. Awareness should be helpful. It would be good to avoid the disorder whenever possible. I think the way in which the arrangement of the collagen fibres produces transparency in the cornea is very impressive, too. Some interesting physics is involved is the process.

Bede from Minnesota on September 27, 2018:

Thanks for making me aware of this infection, Linda. It sounds awful but awareness should lead to greater precautions, especially among contact lens users. I found the fact about the specific arrangement of the collagen fibers most impressive.

Linda Crampton (author) from British Columbia, Canada on September 27, 2018:

Hi, Eman. I appreciate your visit. The keratitis can certainly be harmful. Fortunately, it's still classified as a rare disorder, though the outbreaks that have occurred are worrying.

Eman Abdallah Kamel from Egypt on September 27, 2018:

I know that contact lenses are harmful to the eye, but I did not expect all these disturbances to occur. It's very dangerous. I think it's better not to use it.

Linda Crampton (author) from British Columbia, Canada on September 27, 2018:

Thanks for the visit, Heidi. I think the creatures that live on and in us are very interesting to study.

Linda Crampton (author) from British Columbia, Canada on September 27, 2018:

Hi, Bill. The condition certainly looks unpleasant. I hope the treatments improve.

Heidi Thorne from Chicago Area on September 27, 2018:

I once heard that we would be astounded at the number of organisms living in even our eyes. Good reasons to take care of your contact lenses properly!

Bill Holland from Olympia, WA on September 27, 2018:

Well I'll be darned! That woman's eye looks freaky. I'll be on the lookout for eyes that color now, thanks to you and this article. lol

Linda Crampton (author) from British Columbia, Canada on September 26, 2018:

Hi, Peg. Yes, there is so much to be aware of with respect to our health. The world of living things is interesting and important. Thank you for the visit.

Peg Cole from Northeast of Dallas, Texas on September 26, 2018:

You've explained one of the mysterious diseases that many of us have never even thought about. So many things out there to be aware of. I used to wear contact lenses and often wondered if there were any ill effects of that much contact with my eyes.

Linda Crampton (author) from British Columbia, Canada on September 26, 2018:

Thanks for the comment, Manatita. I hope the visit to the doctor goes well.

manatita44 from london on September 26, 2018:

Seems frightening! Glad that it seems to be rare. Going into Moorfield's on the 1st October, 5 days, woo! Just a check up and probably another fields. I have Glaucoma. Thanks for the refresher.

Linda Crampton (author) from British Columbia, Canada on September 26, 2018:

That sounds like a good idea.

Liz Westwood from UK on September 26, 2018:

Thanks for the quick response, Linda. I think I'll stick with the glasses when swimming.

Linda Crampton (author) from British Columbia, Canada on September 26, 2018:

Thanks for the visit, Liz. The first optician's advice does sound strange. The organism is found in salt water, though I don't know whether that form can cause Acanthamoeba keratitis. It seems like a good idea to assume that it can for safety reasons.

Liz Westwood from UK on September 26, 2018:

As a contact lens wearer I have read your article with added interest. I was aware of the problem, but thank you for explaining it in more detail. I was once told by an optician that it was ok to wear lenses while swimming, but to change to fresh ones afterwards, which I thought a little strange, as did my regular optician. Is this organism found only in tap water etc and not in salt water or is it in both?

Linda Crampton (author) from British Columbia, Canada on September 26, 2018:

Hi, Natalie. Though I've never worn contacts, I've seen how my sister cared for them. It would be nice if the process was quicker and easier so that people could do it even when they were tired.

Linda Crampton (author) from British Columbia, Canada on September 26, 2018:

Hi, Mary. The situation is a concern. We need to learn more about the disease. Some people who don't wear contacts get the disease, though contact lens wearers have a higher risk of being infected. Though most of us don't get infected with the parasite, it's unfortunate for those who do.

Linda Crampton (author) from British Columbia, Canada on September 26, 2018:

Hi, Pamela. It is a horrible disease. I think we're missing an important understanding of the parasite's nature and biology and our body's reaction. As you say, it is a wonder that more people don't become infected.

Linda Crampton (author) from British Columbia, Canada on September 26, 2018:

Hi, Amble. Yes, I think you should definitely ask your GP about your eye problem. It's important that symptoms in the eye that don't quickly disappear—like the ones that you have—are treated. If the symptoms get worse before next week or if they don't improve soon, it would probably be a good idea to get the eye checked earlier.

Natalie Frank from Chicago, IL on September 26, 2018:

Yikes. As a contact lens wearer this is scary. I admit there are those nights when I don't clean my lens quite as well as I should or even reuse the solution that's in the case instead of rinsing it and cleaning it then filing it with new solution. Thanks for the heads up.

Mary Norton from Ontario, Canada on September 26, 2018:

I have not heard of this one before and it is concerning how easy it is for us to get them. Am happy I gave up using contacts a long time ago. Still, there is reason to be concern.

Pamela Oglesby from Sunny Florida on September 26, 2018:

What a horrible disease! I have never worn contact lenses, and I am glad after reading this article. I do have permanent lenses that I received with cataract surgery. It is a wonder more people don't suffer from this condition considering how this organism is located in so many places.

Amble from Surrey United Kingdom on September 26, 2018:

Not being a contact lens wearer perhaps my question is irrelevant.

My left eye is itchy and sore and simply will not stop watering.

Sometimes when I wake up I heat a flannel in the microwave and hold it over my eyes for a minute or two, then wipe therm with cotton wool pads. It doesn't seem to make much difference.

I have a GP appointment next week for something else, should I ask about this? It's just a big nuisance!!

Linda Crampton (author) from British Columbia, Canada on September 25, 2018:

Hi, Flourish. My sister's done the same thing as your father. She started out with glasses, changed to contacts, and is now back to glasses. I know she was very concerned about keeping the contact lenses clean when she wore them. It did seem like a lot of effort from my point of view.

FlourishAnyway from USA on September 25, 2018:

The whole concept of putting a contact lens on your eyeball and wearing it has always struck me as very unclean and given how dirty our hands and environment are, you have further encouraged my uneasiness of them. My dad used to wear contacts but switched back to glasses.

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