Granulomatous amoebic encephalitis overview

# Overview
Granulomatous amoebic encephalitis is a central nervous system disease caused by certain species of amoeba, especially Balamuthia mandrillaris.

# Pathophysiology
Granulomatous amoebic encephalitis is most commonly caused by Acanthamoeba castellanii, A. culbertsoni, A. polyphaga or Balamuthia mandrillaris. It is rarely due to Entamoeba histolytica.

# Epidemiology and Demographics
Balamuthia infection is very rare but often causes fatal disease. Since Balamuthia was first discovered in 1986, about 200 cases of infection have been reported worldwide. This number includes at least 70 confirmed cases in the United States.

# Risk Factors
The Balamuthia amoeba is able to infect  anyone, including healthy people. Those at increased risk for infection include people with HIV/AIDS, cancer, liver disease, or  diabetes mellitus, people taking immune system inhibiting drugs, alcoholics, young  children or the elderly and pregnant women..

# Causes
Balamuthia mandrillaris has only recently been isolated from the environment and has also been isolated from autopsy specimens of infected humans and animals. B. mandrillaris has only two stages, cysts  and trophozoites , in its life cycle. No flagellated stage exists as part of the life cycle. The trophozoites replicate by mitosis (nuclear membrane does not remain intact) . The trophozoites are the infective forms, although both cysts and trophozoites gain entry into the body  through various means. Entry can occur through the nasal passages to the lower respiratory tract , or ulcerated or broken skin . When B. mandrillaris enters the respiratory system or through the skin, it can invade the central nervous system by hematogenous dissemination causing granulomatous amebic encephalitis (GAE)  or disseminated disease , or skin lesions  in individuals who are immune competent as well as those with compromised immune systems. B. mandrillaris cysts and trophozoites are found in tissue.

# Diagnosis

## History and Symptoms
Balamuthia infection is very rare. The Balamuthia amebas can infect the skin, sinuses, brain and other organs of the body. Therefore, Balamuthia infection can cause a wide range of symptoms. Disease  can begin with a skin wound on the face, trunk, or limbs and can then progress  to the brain where it cause a disease called Granulomatous Amebic Encephalitis

## Laboratory Findings
The indirect immunofluorescence assay (IFA) is a test used to detect antibodies attached to Balamuthia amebas in body tissues. In contrast, immunohistochemistry (IHC) uses specific antibodies against Balamuthia to detect the amoebas. Finally, a polymerase chain reaction (PCR) molecular assay can detect Balamuthia DNA.

## MRI
Magnetic resonance imaging (MRI) scans may show increased signal on T2-weighted images. The lesions may show ring enhancement with intravenous contrast studies. Occasionally, there are neuro-radiographic findings of an expanding intracranial mass that may mimic a cerebral tumor or a brain abscess.

## CT
A computerized tomography scan may demonstrate bilateral low-density areas with mild mass effect in the cortex and subcortical white matter.

# Treatment

## Medical Therapy
GAE can, in general, must be treated by killing the pathogenic amoebas which cause it. Even with treatment, the condition is often fatal, and there are very few recorded survivors, almost all of whom suffered permanent neurocognitive deficits. Several drugs have been shown to be effective against GAE-causing organisms in vitro.

## Primary Prevention
Currently, there are no known ways to prevent infection with Balamuthia since it is unclear how and why some people become infected while others do not.
There have been no reports of a Balamuthia infection spreading from one person  to another except through organ donation/transplantation.