Amoebic encephalitis caused by Balamuthia mandrillaris is an emerging disease of importance for both humans and other mammals, including many non-human primates. The opportunistic, free-living, pathogenic amoebic organism is thought to be acquired through the respiratory tract, nasal passages, or breaks in skin; however, much about this disease’s pathogenesis remains unknown.3 Infections are usually fatal and present a diagnostic challenge for both human doctors and veterinarians because of the lack of specific clinical signs and non-invasive antemortem diagnostics.
A 22-year-old, male Western lowland gorilla presented for vague clinical signs in August 2013, which progressed to severe neurologic disease over the course of 10 days despite treatment and supportive care. Gross necropsy revealed hemorrhagic foci within the brain, multifocal tan nodules within the kidneys, and regionally extensive tan areas within the pancreas. Histopathology revealed necrotizing meningoencephalitis and vasculitis with intralesional amoebic organisms. Similar organisms were also identified in granulomatous lesions of the kidney, pancreas, and eye. Immunohistochemistry and PCR analysis of tissue samples confirmed the identity of the organism as Balamuthia mandrillaris.
There have been over 150 reported human cases of this disease worldwide since 1986, although the actual incidence may be higher.2 Although there is no agreed-upon course of treatment, the investigational drug, miltefosine, has shown promise and is available through the CDC.1 Increased awareness of this disease in both veterinary and human medicine has highlighted the importance of collaboration between multiple fields in order to learn more about the biology and pathology of the Balamuthia mandrillaris organism.
We give sincere appreciation to Drs. Atis Muehlenbachs, Alexandre Dasilva, Yvonne Qvarnstrom, and Lindy Liu with the Infectious Disease Pathology Branch and the Parasitic Diseases Branch at the Centers for Disease Control and Prevention for their assistance and cooperation with this case.
1. Centers for Disease Control and Prevention. Investigational drug available directly from CDC for the treatment of infections with free-living amoebae. Morbid Mortal Weekly Rep. 2013;63:666.
2. Diaz JH. The public health threat from Balamuthia mandrillaris in the southern United States. J Louisiana St Med Soc. 2011;163:197–204.
3. Matin A, R Siddiqui, S Jayasekera, NA Kahn. Increasing importance of Balamuthia mandrillaris. Clin Microbiol Rev. 2008;21:435–448.