Free-living amoebae (or "FLA") in the

Amoebozoa Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. In traditional and currently no longer supported classi ...

group are important causes of

disease A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...

in humans and

animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...

s. ''

Naegleria fowleri ''Naegleria fowleri'', colloquially known as a "brain-eating amoeba", is a species of the genus ''Naegleria'', belonging to the phylum Percolozoa, which is technically not classified as true amoeba, but a shapeshifting amoeboflagellate excava ...

'' is sometimes included in the group "free-living amoebae", and it causes a condition traditionally called

primary amoebic meningoencephalitis Naegleriasis (also known as primary amoebic meningoencephalitis; PAM) is an almost invariably fatal infection of the brain by the free-living unicellular eukaryote ''Naegleria fowleri''. Symptoms are meningitis-like and include headache, fever ...

. However, Naegleria is now considered part of the

Excavata Excavata is a major supergroup of unicellular organisms belonging to the domain Eukaryota. It was first suggested by Simpson and Patterson in 1999 and introduced by Thomas Cavalier-Smith in 2002 as a formal taxon. It contains a variety of free- ...

, not the Amoebozoa, and is considered to be much more closely related to ''

Leishmania ''Leishmania'' is a parasitic protozoan, a single-celled organism of the genus '' Leishmania'' that are responsible for the disease leishmaniasis. They are spread by sandflies of the genus ''Phlebotomus'' in the Old World, and of the genus '' ...

'' and ''

Trypanosoma ''Trypanosoma'' is a genus of kinetoplastids (class Trypanosomatidae), a monophyletic group of unicellular parasitic flagellate protozoa. Trypanosoma is part of the phylum Sarcomastigophora. The name is derived from the Greek ''trypano-'' (bore ...

''.

Presentation

''Acanthamoeba spp.'' causes mostly subacute or chronic granulomatous amoebic encephalitis (GAE), with a clinical picture of headaches, altered mental status, and focal neurologic deficit, which progresses over several weeks to death. In addition, ''Acanthamoeba spp.'' can cause granulomatous skin lesions and, more seriously, keratitis and corneal ulcers following corneal trauma or in association with contact lenses.

Life cycle

''Acanthamoeba spp''. and ''Balamuthia mandrillaris'' are opportunistic free-living amoebae capable of causing granulomatous amoebic encephalitis (GAE) in individuals with compromised immune systems. * ''Acanthamoeba spp.'' have been found in soil; fresh, brackish, and sea water; sewage; swimming pools;

contact lens Contact lenses, or simply contacts, are thin lenses placed directly on the surface of the eyes. Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision or for cosmetic ...

equipment; medicinal pools; dental treatment units;

dialysis Dialysis may refer to: *Dialysis (chemistry), a process of separating molecules in solution **Electrodialysis, used to transport salt ions from one solution to another through an ion-exchange membrane under the influence of an applied electric pote ...

machines; heating, ventilating, and air conditioning systems; mammalian cell cultures;

vegetables Vegetables are parts of plants that are consumed by humans or other animals as food. The original meaning is still commonly used and is applied to plants collectively to refer to all edible plant matter, including the flowers, fruits, stems, ...

; human

nostril A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbi ...

s and

throat In vertebrate anatomy, the throat is the front part of the neck, internally positioned in front of the vertebrae. It contains the pharynx and larynx. An important section of it is the epiglottis, separating the esophagus from the trachea (windpipe ...

s; and human and animal brain,

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...

, and

lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...

tissues. * ''B. mandrillaris'' however, has not been isolated from the environment but has been isolated from autopsy specimens of infected humans and animals. Unlike ''N. fowleri'', ''Acanthamoeba'' and ''Balamuthia'' have only two stages, cysts and trophozoites, in their life cycle. No flagellated stage exists as part of the life cycle. The trophozoites replicate by

mitosis In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is mainta ...

(nuclear membrane does not remain intact) . The trophozoites are the infective forms and are believed to gain entry into the body through the

lower respiratory tract The respiratory tract is the subdivision of the respiratory system involved with the process of respiration in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa. Air is breathed in through the nose to th ...

, ulcerated or broken skin and invade the central nervous system by hematogenous dissemination . ''Acanthamoeba spp.'' and ''Balamuthia mandrillaris'' cysts and trophozoites are found in tissue.

Diagnosis

In ''Acanthamoeba'' infections, the diagnosis can be made from microscopic examination of stained smears of biopsy specimens (brain tissue, skin, cornea) or of corneal scrapings, which may detect trophozoites and cysts. Cultivation of the causal organism, and its identification by direct immunofluorescent antibody, may also prove useful. Laboratory workers and physicians often mistake the organisms on wet mount for monocytes and a diagnosis of viral meningitis is mistakenly given if the organisms are not motile. Heating a copper penny with an alcohol lamp and placing it on the wet mount slide will activate sluggish trophozoites and more rapidly make the diagnosis. If the person performing the spinal tap rapidly looks at the heated wet mount slide the trophozoites can be seen to swarm while monocytes do not.

Treatment

Eye and skin infections caused by ''Acanthamoeba spp.'' are generally treatable. Topical use of 0.1%

propamidine isethionate Propamidine is an antiseptic and disinfectant. Propamidine isethionate, the salt of propamidine with isethionic acid, is used in the treatment of ''Acanthamoeba ''Acanthamoeba'' is a genus of amoebae that are commonly recovered from soil, f ...

(Brolene) plus neomycin-polymyxin B-gramicidin ophthalmic solution has been a successful approach;

keratoplasty Corneal transplantation, also known as corneal grafting, is a surgical procedure where a damaged or diseased cornea is replaced by donated corneal tissue (the graft). When the entire cornea is replaced it is known as penetrating keratoplasty ...

is often necessary in severe infections. Although most cases of brain (CNS) infection with ''Acanthamoeba'' have resulted in death, patients have recovered from the infection with proper treatment.

Presentation

Life cycle

Diagnosis

Treatment

Geographic distribution

See also

References

External links