Balamuthiasis: Another Creepy Encephalitis

Not exactly a US public health menace, but the rise of Balamuthia mandrillis encephalitis is something worth watching. The latest issue of the MMWR provides information on 10 cases identified between 1999 and 2007 by the California Encephalitis Project. Since the recognition of balamuthiasis in 1989 (in a pregnant mandrill baboon at the San Diego Zoo), 150 human cases have been identified worldwide.

What is Balamuthia mandrillis?
A free-living amoeba in soil.

How is disease transmitted?
Airborne cysts are inhaled, or skin lesions are directly contaminated.

Who or what is affected?
Immunocompetent or immunocompromised humans, nonhuman primates, horses, dogs, and sheep. People with occupational or recreational exposure to soil (agriculture, construction, dirt biking) may be especially vulnerable.

What are disease symptoms?
Those consistent with other forms of encephalitis—eg, fever, encephalopathy, cranial nerve palsies, seizures.

What does the CSF look like?
Markedly elevated protein (>100 mg/dL); elevated WBC with a predominance of lympocytes; normal or low glucose.

What does brain MRI look like?
Typically abnormal. In the California cases, multiple ring-enhancing lesions, white matter lesions, hypointense lesions, or hydrocephalus were noted.

How is disease definitively diagnosed?
Indirect immunofluorescence staining of formalin-fixed tissue—eg, brain. PCR testing for Balamuthia DNA in CSF or brain tissue has been used; although, the specificity and sensitivity of PCR testing for Balamuthia are unknown, as are the specificity and sensitivity of serologic testing.

Where are reference laboratories? 
At the CDC (gsv1@cdc.gov) and the California Department of Public Health (shilpa.gavile@cdph.ca.gov).

What is the treatment?
Three surviving patients in the United States received pentamidine isethionate, fluconazole, flucytosine, sulfadiazine, and a macrolide antibiotic (azithromycin or clarthromycin).

What is the survival rate?
In the California cases, approximately 10%.

Who or what is Balamuth?
Balamuthia co-discoverer Govinda S. Visvesvara, PhD, of the CDC, writes by e-mail that the organism was named after his major advisor, William Balamuth (1914-1981), Professor of Zoology at UC Berkeley. How's that for homage?

Photomicrograph of Balamuthia mandrillis trophozoites in brain tissue from the CDC.