70-501: Acanthamoeba is a genus of amoebae that are commonly recovered from soil, fresh water , and other habitats . The genus Acanthamoeba has two stages in its life cycle, the metabolically active trophozoite stage and a dormant, stress-resistant cyst stage. In nature, Acanthamoeba species are generally free-living bacterivores . However, they are also opportunistic pathogens able to cause serious and sometimes fatal infections in humans and other animals. Acanthamoeba spp. are among
140-475: A classic model organism in the field of cell biology. From just 30 L of simple medium inoculated with A. castellanii , about 1 kg of cells can be obtained after several days of aerated culture at room temperature. Pioneered in the laboratory of Edward D. Korn at the National Institutes of Health (NIH), many important biological molecules have been discovered and their pathways elucidated using
210-429: A failure to wash hands prior to handling the lenses. Multipurpose contact lens solutions are largely ineffective against Acanthamoeba , whereas hydrogen peroxide-based solutions have good disinfection characteristics. The first cure of a corneal infection was achieved in 1985 at Moorfields Eye Hospital . In May 2007, Advanced Medical Optics, manufacturer of Complete Moisture Plus Contact Lens Solution products, issued
280-424: A mouth or cytostome , and there is no fixed place on the cell at which phagocytosis normally occurs. Some amoebae also feed by pinocytosis , imbibing dissolved nutrients through vesicles formed within the cell membrane. The size of amoeboid cells and species is extremely variable. The marine amoeboid Massisteria voersi is just 2.3 to 3 micrometres in diameter, within the size range of many bacteria. At
350-615: A neurotransmitter acetylcholine in Acanthamoeba and the enzymatic machinery needed for its synthesis. Acanthamoeba spp. contain diverse bacterial endosymbionts that are similar to human pathogens, so they are considered to be potential emerging human pathogens. The exact nature of these symbionts and the benefit they represent for the amoebic host still have to be clarified. These include Legionella and Legionella -like pathogens. The giant viruses Mimivirus , Megavirus , and Pandoravirus infect Acanthamoeba . Members of
420-518: A secondary loss of the amoeboid phase. In his scheme, the Sarcodina were divided into the more primitive Eosarcodina (with the phyla Reticulosa and Mycetozoa) and the more derived Neosarcodina (with the phyla Amoebozoa for lobose amoebae and Rhizopoda for filose amoebae). Shortly after, phylogenetic analyses disproved this hypothesis, as non-amoeboid zooflagellates and amoeboflagellates were found to be completely intermingled with amoebae. With
490-428: A series of molecular phylogenetic analyses confirmed that Sarcodina was not a monophyletic group, and that amoebae evolved from flagellate ancestors. The protozoologist Thomas Cavalier-Smith proposed that the ancestor of most eukaryotes was an amoeboflagellate much like modern heteroloboseans , which in turn gave rise to a paraphyletic Sarcodina from which other groups (e.g., alveolates, animals, plants) evolved by
560-472: A significant role in the development of Acanthamoeba keratitis. In fact, studies of contact lens users in the United Kingdom, Japan, and New Zealand found that 400 to 800 per 10,000 asymptomatic contact lens users had lens storage cases contaminated with Acanthamoeba spp. However, the rate of Acanthamoeba keratitis among these patients was only 0.01 to 1.49 per 10,000 contact lens users. Although
630-402: A single taxonomic group ; instead, they are found in every major lineage of eukaryotic organisms. Amoeboid cells occur not only among the protozoa , but also in fungi , algae , and animals . Microbiologists often use the terms "amoeboid" and "amoeba" interchangeably for any organism that exhibits amoeboid movement . In older classification systems, most amoebae were placed in
700-415: A viral keratitis, such as that caused by varicella zoster virus or herpes simplex virus . As the disease progresses and infiltrates the corneal stroma, a classic "ring infiltrate" may be present on examination (although this is only seen in about 50% of cases). Corneal ulceration , or in severe cases, perforation , can also occur and may be accompanied by hypopyon . In cases of keratitis, diagnosis
770-550: A voluntary recall of their Complete Moisture Plus solutions. The fear was that contact lens wearers who used their solution were at higher risk of acanthamoebic keratitis than contact lens wearers who used other solutions. The manufacturer recalled the product after the Centers for Disease Control in the United States found that 21 people had possibly received an Acanthamoeba infection after using Complete Moisture Plus in
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#1732776647184840-514: Is a rare disease in which amoebae of the genus Acanthamoeba invade the clear portion of the front ( cornea ) of the eye . It affects roughly 100 people in the United States each year. Acanthamoeba are protozoa found nearly ubiquitously in soil and water and can cause infections of the skin, eyes, and central nervous system. Infection of the cornea by Acanthamoeba is difficult to treat with conventional medications, and AK may cause permanent visual impairment or blindness, due to damage to
910-516: Is a list of described species of Acanthamoeba , with sequence types noted where known. Species that have been identified in diseased patients are marked with *. From the Greek akantha (spike/thorn), which was added before "amoeba" (change) to describe this organism as having a spine-like structure ( acanthopodia ). This organism is now well known as Acanthamoeba , an amphizoic, opportunistic, and nonopportunistic protozoan protist widely distributed in
980-544: Is also capable of invading deeper into the cornea; using metalloproteases it is able to penetrate deep into the stroma of the cornea. As the disease progresses, it may penetrate through the cornea but very rarely causes infection inside the eye ( endophthalmitis ) due to a robust neutrophil response in the anterior chamber . While the vast majority of cases of Acanthamoeba keratitis occur in contact lens wearers, there have been many cases of Acanthamoeba described in those who do not wear contact lenses, especially outside
1050-755: Is capable of restoring vision by replacing a damaged cornea, it also carries risks of recurrent Acanthamoeba infection or graft failure. For this reason, anti-amoebic medications should be started prior to surgery, and continued for several weeks afterward. If there is suspicion or evidence of recurrent infection, cultures should be sent. If cultures are positive, anti-amoebic therapy should be continued for 6 months. Outcomes following surgery are typically much better for patients who receive surgery for vision improvement following infection resolution, and therefore all efforts should be made to maximize medical management before attempting surgery. A study in Austria reported
1120-531: Is capable of some form of meiosis and may be able to undergo sexual reproduction. Furthermore, since Acanthamoeba diverged early from the eukaryotic family tree, these results suggest that meiosis was present early in eukaryotic evolution. Owing to its ease and economy of cultivation, the Neff strain of A. castellanii , discovered in a pond in Golden Gate Park in the 1960s, has been effectively used as
1190-410: Is characterized by neurological symptoms including headache, seizures, and mental-status abnormalities. These worsen progressively over weeks to months, leading to death in most patients. Infection is generally associated with underlying conditions such as immunodeficiency , diabetes, malignancies, malnutrition, systemic lupus erythematosus , and alcoholism. The parasite enters the body through cuts in
1260-610: Is diagnosed, initiation of timely and appropriate treatment will have a significant impact on visual outcomes. Medical therapy aims to eradicate both trophozoite and cystic forms of Acanthamoeba and also control the inflammatory response. Multiple classes of drugs have been found to be effective in killing the trophozoite form of Acanthamoeba , including anti-bacterial, anti-fungal, anti-protozoal, and anti-neoplastic agents. However, no single therapy has been found to eliminate both trophozoite and cystic forms, and to eradicate corneal infection. One class of medications used in treatment
1330-431: Is often but not always seen in immunosuppressed patients. GAE is caused by the amoebae entering the body through an open wound and then spreading to the brain. The combination of host immune responses and secreted amoebal proteases causes massive brain swelling resulting in death in about 95% of those infected. Granulomatous amoebic encephalitis (GAE) is caused by amoebic infection of the central nervous system (CNS). It
1400-481: Is often initiated by instilling drops onto the surface of the eye every hour, 24 hours a day, for at least the first 48–72 hours. If an appropriate response to therapy, this may be reduced to hourly administrations during the day only, which is continued for several weeks to months. Beyond anti-amoebic therapies, there is also a role for topical steroids of anti-inflammatory medications in the treatment of Acanthamoeba keratitis. During infection, severe inflammation in
1470-530: Is often misdiagnosed, especially in the early stages of the disease. AK should be considered in all patients who use contact lenses, and following corneal abrasions or trauma. A thorough history should be obtained, especially relating to contact lens use and any recent changes in contact lens solution, exposure of the eyes to water or foreign objects, and symptoms that the patient is experiencing. The symptoms classically attributed to AK include decreased or blurred vision, sensitivity to light ( photophobia ), redness of
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#17327766471841540-401: Is the biguanides , which include polyhexamethylene biguanide (PHMB) 0.02% to 0.06% drops, and chlorhexidine 0.02 to 0.2% drops. These medications disrupt the cell wall of the trophozoite organism, leading to its death. However, these agents have shown limited efficacy against the cystic forms. Due to the efficacy of these drugs against the Acanthamoeba, as well as their low toxicity to
1610-675: Is transferred across the amoeba's cell membrane by osmosis . Without a contractile vacuole, the cell would fill with excess water and, eventually, burst. Marine amoebae do not usually possess a contractile vacuole because the concentration of solutes within the cell are in balance with the tonicity of the surrounding water. The food sources of amoebae vary. Some amoebae are predatory and live by consuming bacteria and other protists . Some are detritivores and eat dead organic material. Amoebae typically ingest their food by phagocytosis , extending pseudopods to encircle and engulf live prey or particles of scavenged material. Amoeboid cells do not have
1680-470: Is typically achieved through evaluation of corneal scrapings. Scrapings are taking from the cornea, and plated on agar for culture, and also can be stained using Gram stain and Giemsa stain to differentiate between bacterial keratitis and AK. To culture Acanthamoeba, scrapings are placed on a non-nutrient agar saline plate seeded with a gram-negative bacteria such as E. coli . If Acanthamoeba are present, they will reproduce readily and become visible on
1750-798: The Acanthamoeba genome . These genes included Spo11 , Mre11 , Rad50 , Rad51 , Rad52 , Mnd1, Dmc1 , Msh and Mlh . This finding suggests that the ‘'Acanthamoeba'’ are capable of some form of meiosis and may be able to undergo sexual reproduction. The meiosis-specific recombinase , Dmc1 , is required for efficient meiotic homologous recombination , and Dmc1 is expressed in Entamoeba histolytica . The purified Dmc1 from E. histolytica forms presynaptic filaments and catalyses ATP -dependent homologous DNA pairing and DNA strand exchange over at least several thousand base pairs . The DNA pairing and strand exchange reactions are enhanced by
1820-512: The Acanthamoeba model. Thomas Dean Pollard applied this model at the NIH, Harvard Medical School , Johns Hopkins University School of Medicine , and the Salk Institute for Biological Studies to discover and characterize many proteins that are essential for cell motility, not only in amoebae, but also in many other eukaryotic cells, especially those of the human nervous and immune systems,
1890-522: The Radiolaria and Heliozoa , have stiff, needle-like, radiating axopodia (actinopoda) supported from within by bundles of microtubules . Free-living amoebae may be " testate " (enclosed within a hard shell), or "naked" (also known as gymnamoebae , lacking any hard covering). The shells of testate amoebae may be composed of various substances, including calcium , silica , chitin , or agglutinations of found materials like small grains of sand and
1960-559: The class or subphylum Sarcodina, a grouping of single-celled organisms that possess pseudopods or move by protoplasmic flow. However, molecular phylogenetic studies have shown that Sarcodina is not a monophyletic group whose members share common descent . Consequently, amoeboid organisms are no longer classified together in one group. The best known amoeboid protists are Chaos carolinense and Amoeba proteus , both of which have been widely cultivated and studied in classrooms and laboratories. Other well known species include
2030-817: The eukaryotic family tree, these results suggest that meiosis was present early in eukaryotic evolution. Furthermore, these findings are consistent with the proposal of Lahr et al. that the majority of amoeboid lineages are anciently sexual. Some amoebae can infect other organisms pathogenically , causing disease: Amoeba have been found to harvest and grow the bacteria implicated in plague . Amoebae can likewise play host to microscopic organisms that are pathogenic to people and help in spreading such microbes. Bacterial pathogens (for example, Legionella ) can oppose absorption of food when devoured by amoebae. The currently generally utilized and best-explored amoebae that host other organisms are Acanthamoeba castellanii and Dictyostelium discoideum. Microorganisms that can overcome
2100-518: The excavates , opisthokonts , stramenopiles and minor clades. The following cladogram shows the sparse positions of amoeboid groups (in bold), based on molecular phylogenetic analyses: Stramenopiles alveolates Rhizaria haptophytes Centroplasthelida plants , etc. euglenids , etc. Heterolobosea CRuMs (incl. Rigifilida ) Amoebozoa Breviatea apusomonads Nucleariids Fungi Acanthamoeba keratitis Acanthamoeba keratitis ( AK )
2170-406: The frustules of diatoms . To regulate osmotic pressure , most freshwater amoebae have a contractile vacuole which expels excess water from the cell. This organelle is necessary because freshwater has a lower concentration of solutes (such as salt) than the amoeba's own internal fluids ( cytosol ). Because the surrounding water is hypotonic with respect to the contents of the cell, water
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2240-567: The plasma membrane that surrounds the cell. The appearance and internal structure of pseudopods are used to distinguish groups of amoebae from one another. Amoebozoan species, such as those in the genus Amoeba , typically have bulbous (lobose) pseudopods, rounded at the ends and roughly tubular in cross-section. Cercozoan amoeboids, such as Euglypha and Gromia , have slender, thread-like (filose) pseudopods. Foraminifera emit fine, branching pseudopods that merge with one another to form net-like (reticulose) structures. Some groups, such as
2310-529: The 20th century. For convenience, all amoebae were grouped as Sarcodina and generally divided into morphological categories , on the basis of the form and structure of their pseudopods . Amoebae with pseudopods supported by regular arrays of microtubules (such as the freshwater Heliozoa and marine Radiolaria ) were classified as Actinopoda , whereas those with unsupported pseudopods were classified as Rhizopoda . The Rhizopods were further subdivided into lobose, filose, plasmodial and reticulose, according to
2380-455: The Austrian zoologist Ludwig Karl Schmarda used "sarcode" as the conceptual basis for his division Sarcodea, a phylum -level group made up of "unstable, changeable" organisms with bodies largely composed of "sarcode". Later workers, including the influential taxonomist Otto Bütschli , amended this group to create the class Sarcodina, a taxon that remained in wide use throughout most of
2450-440: The United States. In non-contact lens users, the greatest risks for developing Acanthamoeba infection are trauma and exposure to contaminated water. Further predisposing factors include contaminated home water supply, and low socioeconomic status. Infection is also more commonly seen in tropical or sub-tropical climates. Beyond the route of inoculation into the eye and external risk factors, host factors are also likely to play
2520-676: The addition of many flagellates to Rhizopoda and the removal of some amoebae, the name was rejected in favour of a new name Cercozoa . As such, both names Rhizopoda and Sarcodina were finally abandoned as formal taxa, but they remained useful as descriptive terms for amoebae. The phylum Amoebozoa was conserved, as it still primarily included amoeboid organisms, and now included the Mycetozoa. Today, amoebae are dispersed among many high-level taxonomic groups. The majority of traditional sarcodines are placed in two eukaryote supergroups : Amoebozoa and Rhizaria . The rest have been distributed among
2590-431: The breakdown of organic matter in soil, contributing to the microbial loop . Because Acanthamoeba does not differ greatly at the ultrastructural level from a mammalian cell, it is an attractive model for cell-biology studies; it is important in cellular microbiology, environmental biology, physiology, cellular interactions, molecular biology, biochemistry, and evolutionary studies, due to the organisms' versatile roles in
2660-607: The case that the Acanthamoeba is diagnosed correctly, the current treatments, such as amphotericin B , rifampicin , trimethoprim - sulfamethoxazole , ketoconazole , fluconazole , sulfadiazine , or albendazole , are only tentatively successful. Correct and timely diagnosis, as well as improved treatment methods and an understanding of the parasite, are important factors in improving the outcome of infection by Acanthamoeba . A paper published in 2013 has shown substantial effects of some FDA-approved drugs with an in vitro kill rate above 90%. These results were in vitro effects, but as
2730-517: The common species now known as Amoeba proteus . The term "Proteus animalcule" remained in use throughout the 18th and 19th centuries, as an informal name for any large, free-living amoeboid. In 1822, the genus Amiba (from the Greek ἀμοιβή amoibe , meaning "change") was erected by the French naturalist Bory de Saint-Vincent . Bory's contemporary, C. G. Ehrenberg , adopted the genus in his own classification of microscopic creatures, but changed
2800-457: The contact lens, Acanthamoeba is able to survive in the space between the contact lens and the surface of the eye. Soft contact lenses are more adherent to the corneal surface than hard lenses, which allows the Acanthamoeba organism to bind to mannosylated glycoproteins on the corneal surface. Expression of these proteins on the corneal surface is increased by contact lens use. This increase in glycoprotein content, along with microtrauma to
2870-407: The cornea and anterior chamber can cause more severe symptoms including pain and visual disturbance. Topical steroids may be used to reduce this inflammation and thereby alleviate symptoms. However, the role of steroids is typically very limited, because their dampening of the immune response may lead to worsening of the infection. Additionally, steroids can increase the number of trophozoites in
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2940-482: The cornea by inducing excystation. Therefore it is typically recommended that steroids be used briefly to aid in symptom resolution, and that anti-amoebic agents be used both during, and for several weeks after topical steroid use. Surgical debridement of an infected cornea can also be used to reduce organism load and excise devitalized tissue from the cornea. It may also improve the efficacy of medical therapy by promoting penetration of medication into deeper layers of
3010-426: The cornea or through damage to other structures important to vision. Recently, AK has been recognized as an orphan disease and a funded project, orphan diseases Acanthamoeba keratitis (ODAK), has tested the effects of a diverse range drugs and biocides on AK. In the United States, Acanthamoeba keratitis is nearly always associated with soft contact lens use. Acanthamoeba spp. is most commonly introduced to
3080-457: The cornea, they are commonly used as the first line medications in the treatment of AK. Biguanides have also been found to act synergistically when used in combination with diamidines , with propamidine isethionate and hexamidine being the most commonly used. A limitation of diamidine use is relative corneal toxicity with long term use. A combined regimen of propamidine , miconazole nitrate, and neomycin has also been suggested. Due to
3150-411: The cornea. In cases of corneal ulceration or perforation, or if corneal scarring is severe, corneal transplant may be required. This typically involves full thickness transplantation of the cornea from a healthy donor eye. The size of the graft should be kept as small as possible, as larger grafts carry a great risk of host rejection, and due to the possibility of graft revision surgery. While surgery
3220-467: The corneal epithelial surface due to contact lens use increases the risk for infection. Once the organism has gained access to the surface of the eye, it is able to invade through the epithelium and Bowman's layer . In some cases, the infection can then group around corneal nerves, producing radial deposits (radial keratoneuritis), and causing extreme pain. These are features also seen in viral and bacterial keratitis , and may be misleading. The organism
3290-478: The defenses of one-celled organisms can shelter and multiply inside them, where they are shielded from unfriendly outside conditions by their hosts. The earliest record of an amoeboid organism was produced in 1755 by August Johann Rösel von Rosenhof , who named his discovery "Der Kleine Proteus" ("the Little Proteus"). Rösel's illustrations show an unidentifiable freshwater amoeba, similar in appearance to
3360-1003: The developing embryo, and cancer cells. Acanthamoeba also has served as a model to study the evolution of certain G-proteins. This unicellular eukaryote expresses few GPCRs over its cell membrane that serve vital role for the microorganism, structural homology bioinformatics tools have been used to show the presence of a homolog of human M1-muscarinic receptor in A. castellanii . Blocking these muscarinic receptors in past studies has proven to be amoebicidal in Acanthamoeba spp. More recently, voltage-gated calcium channels in Acanthamoeba spp. (CavAc) have been reported to have similarities with human voltage-gated calcium channels such as TPC-1 and L-type calcium channels and respond to Ca-channel blockers such as loperamide. This model microbe has been studied to understand complex neurodegenerative states including Alzheimer's disease. Scientists have isolated
3430-408: The drugs are already approved, human infections can be targeted after dose calculations in clinical trials done with these diverse groups of drugs. When present in the eye, Acanthamoeba strains can cause acanthamoebic keratitis , which may lead to corneal ulcers or even blindness. This condition occurs most often among contact lens wearers who do not properly disinfect their lenses, exacerbated by
3500-631: The ecosystem and ability to capture prey by phagocytosis , act as vectors and reservoirs for microbial pathogens, and to produce serious human infections. In addition, Acanthamoeba has been used extensively to understand the molecular biology of cell motility and cancer cell dormancy by in-depth exploration of the process of encystation. The recently available Acanthamoeba genome sequence revealed several orthologs of genes employed in meiosis of sexual eukaryotes . These genes included Spo11 , Mre11 , Rad50 , Rad51 , Rad52 , Mnd1, Dmc1 , Msh , and Mlh . This finding suggests that Acanthamoeba
3570-405: The environment. Amoeboid An amoeba ( / ə ˈ m iː b ə / ; less commonly spelled ameba or amœba ; pl. : amoebas (less commonly, amebas ) or amoebae ( amebae ) / ə ˈ m iː b i / ), often called an amoeboid , is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudopods . Amoebae do not form
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#17327766471843640-430: The eukaryotic meiosis-specific recombination accessory factor (heterodimer) Hop2-Mnd1. These processes are central to meiotic recombination, suggesting that E. histolytica undergoes meiosis. Studies of Entamoeba invadens found that, during the conversion from the tetraploid uninucleate trophozoite to the tetranucleate cyst, homologous recombination is enhanced. Expression of genes with functions related to
3710-506: The exact host factors have not been fully described, it is likely that corneal epithelial defects, tear film composition, eye surface pH, and the level of anti- Acanthamoeba IgA antibodies in the tear film play a role in the development of Acanthamoeba keratitis. Species within the genus, Acanthamoeba , are generally free-living trophozoites . These trophozoites are relatively ubiquitous and can live in, but are not restricted to, tap water, freshwater lakes, rivers and soil. In addition to
3780-491: The eye ( conjunctival hyperemia ), and pain out of proportion to physical exam findings. Another clinical feature that can distinguish Acanthamoeba from bacterial causes of keratitis is a lack of discharge from the eye. On physical exam, findings will depend on the stage of the disease. Early manifestations in the cornea can be seen as punctate keratopathy, pseudodendrites, and epithelial or subepithelial corneal deposits. These features can lead an examiner to confuse AK with
3850-415: The eye by contact lenses that have been exposed to the organism through the use of contaminated lens solution, using homemade saline-based solution or tap water, or from wearing contact lenses while bathing or swimming. However, it may also be introduced to the eye by exposure to soil or vegetation, or by trauma. In fact, the first case of Acanthamoeba keratitis described was due to ocular trauma. Once on
3920-603: The genus Acanthamoeba are unusual in serving as hosts for a variety of giant viruses (that have more than 1000 protein-coding genes; for instance, Pandoravirus , which has about 2500 protein-coding genes in its genome). Acanthamoeba can be distinguished from other genera of amoebae based on morphological characteristics. However, differentiating one species of Acanthamoeba from another by morphology has proven difficult. Based on 18S rDNA sequencing, known Acanthamoeba strains can be organized into 12 groups, denoted T1-T12. Most disease-causing isolates belong to type T4. Below
3990-429: The high prevalence of Acanthamoeba in the environment, these amoebae have been proposed to serve as an environmental reservoir for some human pathogens. A. castellanii can be found at high densities in various soil ecosystems. It preys on bacteria, but also fungi and other protozoa. This species is able to lyse bacteria and produce a wide range of enzymes, such as cellulases or chitinases, and probably contributes to
4060-520: The major steps of meiotic recombination also increase during encystations. These findings in E. invadens , combined with evidence from studies of E. histolytica indicate the presence of meiosis in the Entamoeba . Dictyostelium discoideum in the supergroup Amoebozoa can undergo mating and sexual reproduction including meiosis when food is scarce. Since the Amoebozoa diverged early from
4130-484: The month prior to diagnosis. Several species of bacteria that can cause human disease are also able to infect and replicate within Acanthamoeba species. These include Legionella pneumophila , Pseudomonas aeruginosa , and some strains of Escherichia coli and Staphylococcus aureus . For some of these bacteria, replication inside Acanthamoeba has been associated with enhanced growth in macrophages, and increased resistance to some antibiotics. Furthermore, due to
4200-407: The morphology of their pseudopods. During the 1980s, taxonomists reached the following classification, based exclusively on morphological comparisons: Archezoa Percolozoa (Heterolobosea) other excavates Eosarcodina Neosarcodina Apusozoa → Choanozoa → Animals , Fungi Actinopoda Alveolata → Plants , Chromista In the final decades of the 20th century,
4270-537: The most prevalent protozoa found in the environment. They are distributed worldwide, and have been isolated from soil, air, sewage, seawater, chlorinated swimming pools, domestic tap water, bottled water, dental treatment units, hospitals, air-conditioning units, and contact lens cases. Additionally, they have been isolated from human skin, nasal cavities, throats, and intestines, as well as plants and other mammals. Diseases caused by Acanthamoeba include keratitis and granulomatous amoebic encephalitis (GAE). The latter
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#17327766471844340-540: The other extreme, the shells of deep-sea xenophyophores can attain 20 cm in diameter. Most of the free-living freshwater amoebae commonly found in pond water , ditches, and lakes are microscopic , but some species, such as the so-called "giant amoebae" Pelomyxa palustris and Chaos carolinense , can be large enough to see with the naked eye. Recent evidence indicates that several Amoebozoa lineages undergo meiosis . Orthologs of genes employed in meiosis of sexual eukaryotes have recently been identified in
4410-758: The patients do not have adequate numbers of CD+ve T-cells to mount a granulomatous response to Acanthamoeba infection in CNS and other organs and tissues. A perivascular cuffing with amoebae in necrotic tissue is usual finding in the AIDS and related T-cell immunodeficiency conditions. Brain biopsy normally reveals severe oedema and hemorrhagic necrosis . A patient who has contracted this illness usually displays subacute symptoms, including altered mental status, headaches, fever, neck stiffness, seizures, and focal neurological signs (such as cranial nerve palsies and coma), all leading to death within one week to several months. Due to
4480-431: The plate under 10–20 times objective on an inverted microscope. Polymerase chain reaction (PCR) can be used to confirm a diagnosis of Acanthamoeba keratitis, especially when contact lenses are not involved. Confocal microscopy is a non-invasive technique that allows visualization of Acanthamoeba in vivo in cases in which corneal scraping, culture, and cytology do not yield a diagnosis. Once Acanthamoeba keratitis
4550-401: The potential for negative longterm visual outcomes with AK, therapy is usually started with a combination of a biguanide and a diamidine. Early use of high dose dual therapy helps to eliminate both trophozoite and cyst forms of the organism, while also preventing deep penetration of cysts into the corneal stroma. Cysts that are not eradicated from the cornea will cause recurrence. The treatment
4620-563: The rarity of this parasite and a lack of knowledge, no good diagnoses or treatments for Acanthamoeba infection are now known. Acanthamoeba keratitis cases in the past have resolved from a therapy consisting of atropine and some other drugs with no antimicrobial effects. Recent publications show atropine to interfere with the protist's CHRM1 receptor, causing cell death. Infection usually mimics that of bacterial leptomeningitis , tuberculous meningitis , or viral encephalitis. The misdiagnosis often leads to erroneous, ineffective treatment. In
4690-456: The skin or by being inhaled into the upper respiratory tract. The parasite then spreads through the blood into the CNS. Acanthamoeba crosses the blood–brain barrier by means that are not yet understood. Subsequent invasion of the connective tissue and induction of pro-inflammatory responses leads to neuronal damage that can be fatal within days. Pure granulomatous lesions are rare in patients with AIDS and other related immunodeficiency states, as
4760-440: The so-called "brain-eating amoeba" Naegleria fowleri , the intestinal parasite Entamoeba histolytica , which causes amoebic dysentery , and the multicellular "social amoeba" or slime mould Dictyostelium discoideum . Amoeba do not have cell walls, which allows for free movement. Amoeba move and feed by using pseudopods, which are bulges of cytoplasm formed by the coordinated action of actin microfilaments pushing out
4830-427: The spelling to Amoeba . In 1841, Félix Dujardin coined the term " sarcode " (from Greek σάρξ sarx , "flesh," and εἶδος eidos , "form") for the "thick, glutinous, homogeneous substance" which fills protozoan cell bodies. Although the term originally referred to the protoplasm of any protozoan, it soon came to be used in a restricted sense to designate the gelatinous contents of amoeboid cells. Thirty years later,
4900-407: The trophozoite stage, the organism can also form a double-walled cyst which may also be present in the environment, and can be very difficult to eradicate through medical treatment. Both of these stages are usually non-nucleated and reproduce by the means of binary fission . Due to the relative rarity of Acanthamoeba keratitis (AK) compared to other causes of keratitis (bacterial, viral, etc.), it
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