Free-living amoebae in the Amoebozoa

Amoebozoa

The Amoebozoa are a major group of amoeboid protozoa, including the majority that move by means ofinternal cytoplasmic flow. Their pseudopodia are characteristically blunt and finger-like,...

 group are important causes of disease

Disease

A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...

 in humans and animal

Animal

Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...

s.

Naegleria fowleri

Naegleria fowleri

Naegleria fowleri is a free-living excavate form of protist typically found in warm bodies of fresh water, such as ponds, lakes, rivers, and hot springs. It is also found in soil, near warm-water discharges of industrial plants, and unchlorinated swimming pools in an amoeboid or temporary...

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

Primary amoebic meningoencephalitis

Primary amoebic meningoencephalitis is a disease of the central nervous system caused by infection from Naegleria fowleri.-Presentation:...

. However, Naegleria is now considered part of the Excavata, not the Amoebozoa, and is considered to be much more closely related to Leishmania

Leishmania

Leishmania is a genus of Trypanosomatid protozoa, and is the parasite responsible for the disease leishmaniasis. It is spread through sandflies of the genus Phlebotomus in the Old World, and of the genus Lutzomyia in the New World. Their primary hosts are vertebrates; Leishmania commonly infects...

 and Trypanosoma

Trypanosoma

Trypanosoma is a genus of kinetoplastids , a monophyletic group of unicellular parasitic flagellate protozoa. The name is derived from the Greek trypano and soma because of their corkscrew-like motion. All trypanosomes are heteroxenous and are transmitted via a vector...

.

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 lens
  A contact lens, or simply contact, is a lens placed on the eye. They are considered medical devices and can be worn to correct vision, for cosmetic or therapeutic reasons. In 2004, it was estimated that 125 million people use contact lenses worldwide, including 28 to 38 million in the United...
  
   equipment; medicinal pools; dental treatment units; dialysis
  Dialysis
  In medicine, dialysis is a process for removing waste and excess water from the blood, and is primarily used to provide an artificial replacement for lost kidney function in people with renal failure...
  
   machines; heating, ventilating, and air conditioning systems; mammalian cell cultures; vegetables; human nostril
  Nostril
  A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
  
  s and throat
  Throat
  In vertebrate anatomy, the throat is the anterior part of the neck, in front of the vertebral column. It consists of the pharynx and larynx...
  
  s; and human and animal brain, skin
  Skin
  -Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
  
  , and lung
  Lung
  The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
  
   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

Mitosis

Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...

 (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

Lower respiratory tract

The term lower respiratory tract refers to the portions of the respiratory system from the trachea to the lungs.Lower respiratory tract infections can be the cause of several serious illnesses, including pneumonia....

, 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.

Clinical features

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.

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