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Pathogenic and Opportunistic Free-Living Amebas
Amoeba are described as single-celled eukaryotic beings, existing either freely in nature or as a parasite in a host. These mysteriously ominous creatures are not commonly encountered, but when they are, fatality follows with near certainty. Skilled in attacking unsuspecting victims where they can be the most vulnerable, amoeba can be found in places such as still freshwater bodies of water, saline contact solution, and even dialysis machines. These creatures are known to survive by attaching themselves to a host and feeding on that host until its hasty demise. With a miniscule number of new cases each year, amoeba are nearly synonymous with obscurity and fatality, due to the grim mortality rate associated with the species and the little we know about them. This text explores the pathogenesis methodology, molecular characterization, immunology, and taxonomy of four distinct amoeba species, Acanthamoeba spp., Balamuthia mandrillaris, Naegleria fowleri, and Sappinia diploidea.
There are more than twenty-four species of Acanthamoeba that we are currently aware of (Visvesvara). Acanthamoeba are found ubiquitously worldwide, and most individuals that come into contact with the organism are never affected in any way. To emphasize the omnipresence of the Acanthamoeba, they have been found in places such as bottled mineral water, dialysis machines, contact lens paraphernalia, heating, ventilating, and, air conditioning (HVAC) systems, stool samples, and more (CDC). Classification of the species relies heavily on morphological characteristics. Acanthamoeba have two life cycle stages, one that consists of feeding and one characterized by resistant sleeping. The fine, thorn-like pseudopods known as acanthopodia are responsible for moving the species around its environment. Acanthamoeba are generally easy to satisfy, as they only require food and a warm moist environment to survive. In nature, this organism feeds on edible bacteria from its environment, but as a parasite, the organism feeds on extremely vital and delicate tissues within the human body. As they feast, Acanthamoeba can multiply within days.
One disease caused by Acanthamoeba is Acanthamoeba Keratitis (AK). The first case of AK was documented in Texas in 1973. AK is an eye infection that typically develops when a contact lens wearer uses an amoeba-contaminated saline solution. This infection is especially acute and can ultimately lead to blindness. Symptoms associated with AK include blurred vision, pain in the eye, light sensitivity, and overwhelming tearing. The infection tends to be severe due to the repeated use of a contaminated saline solution. Because of this, the Center for Disease Control (CDC) urges contact wearers to be especially cognizant of proper lens storage, handling, and disinfection, and swimming while wearing contact lenses.
Balamuthia is very similar to the beforementioned Acanthamoeba in morphology and life cycle. Balamuthia was first discovered in 1986 after scientists found the parasite in the brain of a dead baboon. Since 1993 however, there have been over two hundred cases in humans. In nature, Balamuthia has been found in samples collected from soil and dust. While we are not entirely sure on what Balamuthia’s natural food supply is, we can assume they feed on bacteria as well. Similar to Acanthamoeba, Balamuthia also leads to a form of GAE, however, this form targets children and seemingly healthy adults. The parasite enters the body through cuts on the skin or the inhalation or ingestion of Balamuthia-contaminated dust particles. Symptoms associated with this disease include headaches, seizures, difficulty walking and speaking in full sentences, low grade fever, and stiff neck. The death rate associated with this disease is eighty-nine percent.
Naegleria fowleri was first discovered in Australia in 1965. It has an extremely rare infection rate, as only ten people were affected by the parasite between the years of 2001 and 2010. Smaller than a human hair, this organism enters the body though the nose and finds its way to the brain by detecting special secretions from the olfactory nerve. (Visvesvara) The organism travels along the olfactory nerve until it makes its way to the frontal lobe where it begins feasting and multiplying. Naegleria loves warm environments and the brain is the perfect place for it to thrive. Outside of the body, Naegleria can be found in hot springs, warm rivers and lakes, and soil. In these places, the Naegleria find food sources within the sediment around them (Sullivan). Because this is a thermophilic organism, reports of infection typically occur in the summer in southern regions. Out of all 146 cases, only four people have survived, meaning the infection caused by Naegleria has a mortality rate of 97% (CDC). This infection, Primary Amebic Meningoencephalitis (PAM) is characterized by brain tissue deterioration. Symptoms of the disease typically present themselves after five days of infection and include headache, nausea, fever, and vomiting. Death also manifests after about five days of infection. The majority of PAM diagnoses are made after the death of the infected individual.
Sappinia diploidea is unique from the previously listed amoebas in a few ways. Firstly, this parasite is primarily found near animals and rotten plants, including buffalo and elk feces, places where animals are known to graze, and freshwater deposits. This amoeba can enter the body via cuts on the skin or the nose. Infection from these interaction seems to be more likely in those who regularly interact with feces or those with compromised immune systems (Sappinia). The infection caused, Amebic encephalitis, has only one known case where infection was not fatal – extremely rare in the case of amoebas. Symptoms associated with this infection include headache, nausea, vomiting, blurry vision, and loss of consciousness. In the one case of amebic encephalitis, the patient was treated in the hospital and made a full recovery.
It would be ideal for amoeba found in the natural environment to remain there, but it is certainly quite impossible. Many issues arise when discussing proper preventative measures surrounding amoeba, because there are currently no ways to detect the presence of the organisms in associated environments. The CDC infers that recreational swimmers should be aware but not alarmed due to the rarity of infection, however, the mortality rate negates all reassurances from the entity. What makes amoeba all the more terrifying is the fact that symptoms don’t clearly present themselves early, nor are they distinguishable between each other. The infections associated with each amoeba had symptoms of headaches, nausea, and fever, making it extremely difficult to pinpoint which bacteria has infected an individual. Another point is there are no concise testing measures for these diseases, and the results come back late in too many cases – after the individual has already succumbed to the infection. Because there is no way of foreknowing who will be affected, when, and how, amoebas stand as one of the deadliest natural enigmas the world has seen.
- Acanthamoeba – Granulomatous Amebic Encephalitis (GAE); Keratitis | Acanthamoeba | Parasites | CDC. 2017 Jun 5 [accessed 2019 Sep 5]. https://www.cdc.gov/parasites/acanthamoeba/
- Balamuthia | Parasites | CDC. 2016 Feb 17 [accessed 2019 Sep 2]. https://www.cdc.gov/parasites/balamuthia/index.html
- Primary Amebic Meningoencephalitis (PAM) – Naegleria fowleri | Parasites | CDC. 2017 Feb 28 [accessed 2019 Sep 2]. https://www.cdc.gov/parasites/naegleria/index.html
- Sappinia – Amebic Encephalitis | Sappinia | Parasites | CDC. 2011 Mar 8 [accessed 2019 Sep 10]. https://www.cdc.gov/parasites/sappinia/
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- Visvesvara GS, Maguire JH. Pathogenic and Opportunistic Free-Living Amebas: Acanthamoeba spp., Balamuthia mandrillaris, Naegleria fowleri, and Sappinia diploidea. 2007 [accessed 2019 Sep 1];50(1):1114–1125.
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