Balamuthia mandrillaris

Balamuthia mandrillaris
Balamuthia in cyst form.
Balamuthia mandrillaris in active form.
Scientific classification
Domain:	Eukaryota
Kingdom:	Amoebozoa
Class:	Lobosea
Order:	Centramoebida
Family:	Balamuthiidae
Genus:	Balamuthia
Species:	B. mandrillaris
Binomial name
Balamuthia mandrillaris

Balamuthia mandrillaris is a free-living amoeba that is known to cause a type of amoebiasis in humans,^[1] especially the deadly neurological condition known as granulomatous amoebic encephalitis (GAE).^[2] B. mandrillaris is found in the environment and was first discovered in 1986 in the brain of a baboon that died in the San Diego Wild Animal Park. B. mandrillaris can infect the body through skin wounds or by inhaling the dust containing Balamuthia.^[3] 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 (1914-1981) for his contributions to the studies of parasitic and free-living amoebas.

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.^[4]

Life cycle

Balamuthia's life cycle, like Acanthamoeba, 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. The trophozoite is pleomorphic and uninucleated, but binucleate forms are occasionally seen. Cysts are also uninucleated possessing three walls: an outer thin irregular ectocyst, an inner thick endocyst, and a middle amorphous fibrillar mesocyst.^[5]

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,^[6] 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 amoebic keratitis, and usually results in facial swelling.

Balamuthia encephalitis is an extremely deadly disease, and as of 2008, only seven recoveries had been reported,^[7] all with lasting brain damage.

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.^[8]

Treatment

Balamuthia infection has had successful treatments. 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. Another two cases were presented and both of these individuals received successful treatments due to discovering the infection early. Two individuals, a five-year-old girl and a 64 year old man, developed encephalitis caused by the free living B. mandrilaris. After diagnosed, they were given effective antimicrobial therapy. Both patients recovered.^[9]

Organ transplantation

According to a MMWR report published in September 2010, 2 confirmed cases of balamuthia transmission occurred through organ transplantation in December 2009 in Mississippi. Two kidney recipients, a 31 year old woman and a 27 year old man, suffered from post transplant encephalitis due to balamuthia. The woman died in February 2010 and the man survived with partial paralysis of right arm. The CDC was notified by a physician on December 14, 2009 about possible transplant transmission in these two patients. Histopathologic testing of donor and recipient tissues confirmed the transmission. Two other patients who received heart and liver transplants from the same donor but in different hospitals were placed on preemptive therapy and remain unaffected. A second cluster of transplant transmitted balamuthia in Arizona was reported in the same weekly report. There were four recipients two from Arizona- liver and kidney-pancreas, one from California- kidney and another from Utah-heart. Recipients from Arizona-a 56 year old male and a 24 year old male, both succumbed to encephalitis within a span of 40 days from transplantation. The other two were placed on preemptive therapy after the first two were reported and remain unaffected.

References

External links

• http://www.cdc.gov/balamuthia/index.html for images: Cyst of B. mandrillaris and Trophozoite of B. mandrillaris in culture. Credit: DPDx