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Balamuthia mandrillaris
Scientific classification
Domain: Eukaryota
Kingdom: Amoebozoa
Family: Balamuthiidae
Genus: Balamuthia
Species: B. mandrillaris
Binomial name
Balamuthia mandrillaris

Balamuthia mandrillaris is a free-living leptomyxid amoeba which is known to cause amoebiasis in humans,[1] especially the deadly neurological condition known as primary amoebic meningoencephalitis. Balamuthia has not been definitively isolated in nature, but it is believed to be distributed throughout the temperate regions of the world. This is supported somewhat by the presence of antibodies to Balamuthia present in healthy individuals. The Balamuthia genus is named in honor of the late Professor William Balamuth for his contributions to the studies of parasitic and free-living amoebas.

Contents

Morphology

Balamuthia mandrillaris is a free-living, heterotrophic amoeba, consisting of a standard complement of organelles surrounded by a three-layered cell wall, and with an abnormally large, vesicular nucleus. On average, a Balamuthia trophozoite is approximately 30–120 µm in diameter. The cysts fall approximately in this range as well. [2]

Life cycle

Balamuthia's life cycle consists of a cystic stage and a trophozoite stage, both of which are infectious, and both of which can be identified as inclusions in the brain tissue on microscopic examination of brain biopsies performed on infected individuals.

Pathology

Balamuthia mandrillaris may enter the body through the lower respiratory tract or through open wounds. Upon introduction, the amoebas may form a skin lesion, or migrate to the brain. Once in the brain, Balamuthia causes a condition known as granulomatous amoebic encephalitis (GAE), which is usually fatal. The symptoms of infection by Balamuthia are unclear, as only a few definitive cases of Balamuthia infection have been described thus far. Balamuthia-induced GAE can cause focal paralysis, seizures, and brainstem symptoms such as facial paralysis, difficulty swallowing, and double vision.

Balamuthia is also known to cause a variety of non-neurological symptoms, and often causes skin lesions, through which the amoeba may enter the bloodstream and migrate to the brain. Many patients experiencing this particular syndrome report a skin lesion (sometimes similar to those caused by Staphylococcus aureus or other bacteria), which does not respond well to dermatologic treatment. The lesion is usually localised and very slow to heal, or fails to heal altogether. In some presentations, the lesion may be mistaken for certain forms of skin cancer. Balamuthia lesions on the face may also lead to amebic keratitis, and usually results in facial swelling.

Balamuthia encephalitis is an extremely deadly disease, and as of 2008, only seven recoveries had been reported[3], all with lasting brain damage.

Prevalence

Infection with Balamuthia is extremely rare, and the amoeba is not considered a cause for public health concern, despite its wide geographic range, since only immunocompromised individuals are at a significant risk of contracting Balamuthia meningoencephalitis.

The first case of infection transmitted from an allogeneic transplant was reported in December 2009, when two kidney transplant recipients became infected after each received a kidney from the same infected donor. Two recipients of other organs from the donor failed to become infected.[4]

Culturing and identification

Balamuthia is most easily identifiable in a brain biopsy performed on an individual suffering from Balamuthia meningoencephalitis. The amoeba cannot be cultured on an agar plate coated with gram-negative bacteria because unlike most amoeba, Balamuthia mandrillaris does not feed on bacteria. Instead the amoeba must be cultured on primate hepatic cells or human brain microvascular endothelial cells, or HBMECs, the cells that constitute the blood-brain barrier. [5]

Treatment

Balamuthia infection has only been successfully treated in two cases. Both were treated with a cocktail of antibiotics and antiparasitics, although it is unclear if any or all of these medications played a part in treatment. Both victims suffered permanent neurological deficits as a result of their infection.

Deaths related to Balamuthia mandrillaris

Matt Moore, a firefighter from Murrieta, California, fell ill in November 2007. When a biopsy was done in January 2008, they found his brain had been invaded by Balamuthia mandrillaris. He died on March 10, 2008.[6] According to the California Encephalitis Project report published in the July 18, 2008 Morbidity and Mortality Weekly Report, a total of 10 encephalitis cases were known to have been caused by the amoeba between 1997 and 2007.

First known case by organ transplantation

On December 9, 2009, the first known cases of infection by organ transplantation were reported by University of Mississippi Medical Center.[7]

Other pathogenic amoebas

Related amoebas

See also

References

  1. ^ Recavarren-Arce S, Velarde C, Gotuzzo E, Cabrera J (March 1999). "Amoeba angeitic lesions of the central nervous system in Balamuthia mandrilaris amoebiasis". Hum. Pathol. 30 (3): 269–73. doi:10.1016/S0046-8177(99)90004-7. PMID 10088544.  
  2. ^ Dunnebacke TH, Schuster FL, Yagi S, Booton GC (September 2004). "Balamuthia mandrillaris from soil samples". Microbiology (Reading, Engl.) 150 (Pt 9): 2837–42. doi:10.1099/mic.0.27218-0. PMID 15347743. http://mic.sgmjournals.org/cgi/content/full/150/9/2837.  
  3. ^ Balamuthia
  4. ^ http://www.nytimes.com/2009/12/19/health/19transplant.html
  5. ^ Martínez AJ, Visvesvara GS (March 2001). "Balamuthia mandrillaris infection". J. Med. Microbiol. 50 (3): 205–7. PMID 11232763. http://jmm.sgmjournals.org/cgi/pmidlookup?view=long&pmid=11232763.  
  6. ^ CBS 13 AP News Report
  7. ^ CDC: Rare infection passed on by Miss. organ donor

External links

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