Balamuthia mandrillaris

Balamuthia mandrillaris is considered is a free living ameba that is a an uncommon cause of meningoencephalitis.

Disease / Pathology

Balamuthia mandrillaris is a free living ameba that is thought to be of soil origin. It is an uncommon cause of amebic encephalitis. The amebic encephalitis is similar to GAE (Granulomatous amebic encephalitis) seen in Acanthamoeba central nervous system infections. The source is not from water as in Naegleria fowleri. As with Acanthamoeba the clinical course of the infection tends to be subacute or chronic. The infection in the brain tends to mainly involve the cerebral cortex and subcortical white matter. Symptoms of infection include nausea, fever, vomiting, seizures, headaches, visual disturbances, dysphasia. Imaging of the brain may suggest septic infarcts, a neoplasm, or tuberculous. All of which may make a diagnosis difficult.

As is true with most uncommon infections, an impaired immune state is critical in predisposing one to an infection with Balamuthia mandrillaris.

Location in the Host

Balamuthia mandrillaris is introduced into the host through either nasal passages leading to the lower respiratory tract or through ulcerated or broken skin. From there the ameba will disseminate and eventual entry into the brain to cause GAE.

Geographic Distribution

Balamuthia mandrillaris with a worldwide distribution, the most important to consider is the source. As of yet no conclusive source has been made but most evidence points to soil.

Life Cycle

Morphology & Diagnosis

Balamuthia mandrillaris trophozoites are 12-60um in length of irregular shape.

The cysts are spherical and measure 6-30um in diameter. Under light microscopy the cysts appear to have two walls. The outer wall appears as irregular while the inner wall is smooth and round.

Both forms of the ameba can be seen in tissue sections of brain infected with the ameba. The ameba, like Acanthamoeba app., does not have a flagellated stage in its life cycle like Naegleria fowleri does.


Balamuthia mandrillaris trophozoites in brain tissue in GAE case – photo courtesy of CDC/NCID/DPDx