It is rare for the organism acanthamoeba to cause disease, because it is not a parasite. But it can cause inflammation of the brain in people who have been ill for quite some time and in those who have a weak immune system. It can also cause eye inflammation in contact lens wearers.
What is Acanthamoeba?
Microbiologists call acanthamoeba a "free-living" ameba because it does not have to have an animal or human to survive. It lives freely and independently in the soil and in warm, freshwater lakes, according to Warren Levinson, M.D., Ph.D., Professor of Microbiology at the University of California in "Review of Medical Microbiology and Immunology." It moves freely as an ameba, but it also lives as a cyst. Water chlorination does not kill the cyst form. Acanthamoeba can cause disease, but it is rare.
Granulomatous Amebic Encephalitis
Acanthamoeba causes a disease called granulomatous amebic encephalitis. This disease primarily affects people who have been ill for quite some time, or those with a weak immune system. Some of the people who are at risk of contracting this disease include those taking glucocorticoids or receiving chemotherapy, people with AIDS or lupus. As explained by Dr. Levinson in "Review of Medical Microbiology and Immunology," an acanthamoeba infection in the lungs, skin or sinuses will get into the bloodstream. The ameba travels through the blood and reaches the brain. Symptoms slowly develop and include headache, mental confusion, stiff neck, lack of coordination and paralysis on one side of the body. People with AIDS may have nodules or skin ulcers that contain the ameba.
Evaluation for Granulomatous Amebic Encephalitis
Dr. Levinson writes that a positive diagnosis for this disease is when the pathologist sees the ameba or cyst on a microscope slide, or in a biopsy. The Centers for Disease Control and Prevention has substances the pathologist can use to help detect it in a biopsy specimen. A CT scan of the head may show lesions or lesions along with swollen areas. It may also show embolic infarcts, or areas of dead tissue, where an embolus, or clot, has stopped the flow of blood and oxygen to that area.
Amebic Keratitis
Keratitis is the inflammation of the cornea of the eye, or the clear part of the eye in front of the pupil. Unlike granulomatous amebic encephalitis, this disease affects people who are normally healthy, according to Richard Pearson, M.D. in "The Merck Manual for Healthcare Professionals." People are at risk of contracting amebic keratitis if they wear contact lenses, as 85 percent of those with this disease wear contacts. They are especially at risk if they use contact cleaning solutions that are not sterile, or wear contacts while they swim. Some people get amebic keratitis after they get scratches on their cornea. This disease is very painful and feels as though there is something in the eye.
Evaluation for Amebic Keratitis
Dr. Levinson writes in "Review of Medical Microbiology and Immunology," that over the past 20 years, there have been an increasing number of cases of amebic keratitis, partially because physicians can better evaluate for this ameba. The pathologist can check for the cyst form in scrapings from the cornea, or in a biopsy sample. The lab can grow acanthamoeba in a special media.
References
- "Review of Medical Microbiology and Immunology," Warren Levinson, M.D., Ph.D.; 2008
- The Merck Manual for Healthcare Professionals: Free-Living Amebas
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