Granulomatous amoebic encephalitis epidemiology and demographics

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

Epidemiology and demographics
An open wound, such as a cut or scrape, may be a potential entry point for Balamuthia.

Balamuthia infection is very rare but often causes fatal disease[1]. Since Balamuthia was first discovered in 1986, about 200 cases of infection have been reported worldwide[2,3,4]. This number includes at least 70 confirmed cases in the United States. Because disease caused by Balamuthia is so uncommon, it is possible that there have been additional cases that were misdiagnosed [2,4].

Balamuthia amebas (single-celled living organisms) are thought to enter the body when soil containing Balamuthia comes in contact with skin wounds and cuts, or when dust containing Balamuthia is breathed in or gets in the mouth[1]. Once inside the body, the amebas can then travel to the brain and cause Granulomatous Amebic Encephalitis (GAE)[1]. GAE is a severe disease of the brain that is fatal in over 95% of cases[2]. It can take weeks to months to develop the first symptoms of Balamuthia GAE after initial exposure to the amebas[2,3].

Balamuthia amebas live freely in soil around the world[1-13]. Gardening, playing with dirt, or breathing in soil carried by the wind might increase the risk for infection[1,2,5]. Balamuthia might also be present in fresh water[1]. There have been reports of Balamuthia GAE infection  in dogs that swam in ponds. However, there have been no reported human cases where the only potential exposure was swimming.

The Balamuthia ameba is able to infect anyone, including healthy people[1-6]. Those at increased risk for infection[1-4,6,10] include:

People with HIV/AIDS, cancer, liver disease, or diabetes mellitus People taking immune system inhibiting drugs Alcoholics Young children or the elderly Pregnant women

In the United States, Balamuthia infection might be more common among Hispanic Americans[6,13]. However, the cause of this trend is unknown and might be due to differences in exposure, biology, data collection, or other reasons[1,13-17]. More research is needed to understand what factors might be associated with increased reporting among persons of  Hispanic ethnicity.

There have been no reports of a Balamuthia infection spreading from one person to another except through organ donation/transplantation.