Related Experiment Video
Updated: Jan 22, 2026
Discovery of New Intracellular Pathogens by Amoebal Coculture and Amoebal Enrichment Approaches
Published on: October 27, 2013
Pathogenic free-living amoebic encephalitis in Japan
Tatsuru Hara1, Kenji Yagita2, Yasuo Sugita3
1Department of Parasitology, Kurume University School of Medicine, Kurume, Japan.
Abstract:
Over 600 cases of amoebic encephalitis caused by pathogenic free-living amoebas (Balamuthia mandrillaris, Acanthamoeba spp., and Naegleria fowleri) have been reported worldwide, and in Japan, 24 cases have been reported from the first case in 1976 up to 2018. Among these cases, 18 were caused by B. mandrillaris, four by Acanthamoeba spp., one by N. fowleri, and one was of unknown etiology. Additionally, eight cases were diagnosed with encephalitis due to pathogenic free-living amoebas before death, but only three cases were successfully treated. Unfortunately, all other cases were diagnosed by autopsy. These facts indicate that an adequate diagnosis is difficult, because encephalitis due to pathogenic free-living amoebas does not show typical symptoms or laboratory findings. Moreover, because the number of cases is limited, other cases might have been missed outside of those diagnosed by autopsy. Cases of encephalitis caused by B. mandrillaris have been reported from all over Japan, with B. mandrillaris recently isolated from soil in Aomori prefecture. Therefore, encephalitis caused by pathogenic free-living amoebas should be added to the differential diagnosis of encephalitis patients.
Insights
Free-living amoebic encephalitis is rare but difficult to diagnose. Early consideration in differential diagnosis is crucial for potential treatment of these serious infections.
Area of Science:
- Neurology
- Infectious Diseases
- Microbiology
Background:
- Over 600 cases of pathogenic free-living amoeba encephalitis reported globally.
- Japan has reported 24 cases between 1976 and 2018, primarily Balamuthia mandrillaris.
- Diagnosis is challenging due to non-specific symptoms and reliance on autopsy.
Purpose of the Study:
- To highlight the diagnostic challenges of free-living amoebic encephalitis.
- To emphasize the need for including amoebic encephalitis in differential diagnoses.
Main Methods:
- Review of reported cases of amoebic encephalitis in Japan.
- Analysis of etiological agents and diagnostic timing.
- Consideration of environmental isolation of Balamuthia mandrillaris.
Main Results:
- Balamuthia mandrillaris was the most common cause in Japan (18/24 cases).
- Only 3 of 8 pre-mortem diagnosed cases were successfully treated.
- Most cases were diagnosed post-mortem, indicating diagnostic difficulties.
Conclusions:
- Encephalitis caused by pathogenic free-living amoebas presents diagnostic challenges.
- Balamuthia mandrillaris is a significant cause in Japan, with environmental isolates found.
- Consideration of amoebic encephalitis in the differential diagnosis of encephalitis is recommended.
Related Concept Videos
02:26Defenses Against Pathogens and Herbivores
01:31Defense Against Bacterial Pathogens
Phagocytes
Phagocytes are the frontline soldiers of the immune system. They include neutrophils and macrophages. Neutrophils are the most abundant type of white blood cell and are quickly mobilized to the site of infection. Macrophages are larger cells that patrol...
01:29Immune Response Against Viral Pathogens
NK Cells
NK cells are a crucial part of our innate immune system, acting as the first line of defense against viral infections. These cells can recognize and kill infected cells without prior exposure to the virus, effectively slowing down the spread of infection. Additionally, NK cells produce proinflammatory...
01:19Protein Dynamics in Living Cells
Fluorescent recovery after photobleaching (FRAP) is a fluorescent-protein-based detection technique used to quantify protein movement rates within the cell. This method exposes a small portion of the cell to an intense laser beam. The laser beam causes permanent photobleaching of the fluorophore-tagged proteins in the exposed region. As the bleached...
02:11The Roles of Bacteria and Fungi in Plant Nutrition
01:36Humoral Immune Responses