Balamuthia mandrillaris amoebic encephalitis （BAE） is a rare infectious disease with a high mortality rate and is caused by Balamuthia mandrillaris. The lack of specific clinical manifestations often leads to misdiagnosis. This article reports a case of BAE diagnosed by metagenomic next-generation sequencing， in order to improve the understanding of the disease.
Balamuthia mandrillaris

Infection of the human central nervous system by Balamuthia mandrillaris is very rare and is mostly observed in people engaged in agriculture-related occupations，with a high fatality rate. This article reports a case of Balamuthia mandrillaris amoebic encephalitis in southern Hunan, China，which was finally confirmed by metagenomic next-generation sequencing of cerebrospinal fluid. The patient gave up treatment and was discharged from the hospital without achieving remission after antiviral，anti-fungal，and anti-parasitic therapies，cranial pressure reduction，and symptomatic supportive treatment，and the patient died at 5 months after confirmed diagnosis. This article reviews related literature to improve the understanding of this disease among clinicians，and it is necessary to consider the possibility of this disease in case of encephalitis of unknown etiology. Early diagnosis and timely comprehensive anti-infective therapy should be performed to improve the success rate of treatment.
Balamuthia mandrillaris

Among various genera of free-living amoebae prevalent in nature, some members are identified as causative agents of human encephalitis, in which Naegleria fowleri followed by Acanthamoeba spp. and Balamuthia mandrillaris have been successively discovered. As the three dominant genera responsible for infections, Acanthamoeba and Balamuthia work as opportunistic pathogens of granulomatous amoebic encephalitis in immunocompetent and immunocompromised individuals, whereas Naegleria induces primary amoebic meningoencephalitis mostly in healthy children and young adults as a more violent and deadly disease. Due to the lack of typical symptoms and laboratory findings, all these amoebic encephalitic diseases are difficult to diagnose. Considering that subsequent therapies are also affected, all these brain infections cause significant mortality worldwide, with more than 90% of the cases being fatal. Along with global warming and population explosion, expanding areas of human and amoebae activity in some regions lead to increased contact, resulting in more serious infections and drawing increased public attention. In this review, we summarize the present information of these pathogenic free-living amoebae, including their phylogeny, classification, biology, and ecology. The mechanisms of pathogenesis, immunology, pathophysiology, clinical manifestations, epidemiology, diagnosis, and therapies are also discussed.
Amebiasis/epidemiology* ; Balamuthia mandrillaris ; Brain ; Central Nervous System Protozoal Infections/epidemiology* ; Child ; Humans ; Naegleria fowleri

We present the case of a 71-year-old man who was diagnosed with amoebic encephalitis caused by Balamuthia mandrillaris. He had rheumatic arthritis for 30 years and had undergone continuous treatment with immunosuppressants. First, he complained of partial spasm from the left thigh to the left upper limb. Magnetic resonance imaging revealed multifocal enhancing nodules in the cortical and subcortical area of both cerebral hemispheres, which were suggestive of brain metastases. However, the patient developed fever with stuporous mentality and an open biopsy was performed immediately. Microscopically, numerous amoebic trophozoites, measuring 20 to 25 µm in size, with nuclei containing one to four nucleoli and some scattered cysts having a double-layered wall were noted in the background of hemorrhagic necrosis. Based on the microscopic findings, amoebic encephalitis caused by Balamuthia mandrillaris was diagnosed. The patient died on the 10th day after being admitted at the hospital. The diagnosis of amoebic encephalitis in the early stage is difficult for clinicians. Moreover, most cases undergo rapid deterioration, resulting in fatal consequences. In this report, we present the first case of B. mandrillaris amoebic encephalitis with fatal progression in a Korean patient.
Aged ; Balamuthia mandrillaris ; Biopsy ; Brain ; Cerebrum ; Diagnosis ; Encephalitis ; Fever ; Humans ; Immunosuppressive Agents ; Magnetic Resonance Imaging ; Necrosis ; Neoplasm Metastasis ; Rheumatic Fever ; Spasm ; Stupor ; Thigh ; Trophozoites ; Upper Extremity