An autopsy case of Balamuthia mandrillaris amoebic encephalitis, a rare emerging infectious disease, with a brief review of the cases reported in Japan

Abstract

Balamuthia mandrillaris is an amoeba found in fresh water and soil that causes granulomatous amoebic encephalitis. We report herein an autopsy case of B. mandrillaris amoebic encephalitis, which was definitely diagnosed by PCR. An 81-year-old man, who had Sjögren's syndrome, manifested drowsiness 2 months before his death with progressive deterioration. Neuroimaging demonstrated foci of T2- and fluid-attenuated inversion recovery high and T1 low-intensity with irregular post-contrast ring enhancement in the cerebral hemisphere, thalamus and midbrain. Pathologically, multiple hemorrhagic and necrotic lesions were found in the cerebrum, thalamus, midbrain, pons, medulla and cerebellum, which were characterized by liquefactive necrosis, marked edema, hemorrhage and necrotizing vasculitis associated with the perivascular accumulation of amoebic trophozoites, a few cysts, and the infiltration of numerous neutrophils and microglia/macrophages. The trophozoites were ovoid or round, 10-60 μm in diameter, and they showed foamy cytoplasm and a round nucleus with small karyosome in the center. The PCR and immunohistochemistry from paraffin-embedded brain specimens revealed angioinvasive encephalitis due to B. mandrillaris. Human cases of B. mandrillaris brain infection are rare in Japan, with only a few brief reports in the literature.

Microglia in neuropathology caused by protozoan parasites

“…Areas of the brain with microglial accumulation have been reported for many different parasitic diseases. A post‐mortem examination from an 81‐year‐old male patient infected with the amoeba Balamuthia mandrilaris showed microglial cells surrounding necrotic lesions in the thalamus, midbrain, pons, medulla, and cerebellum, where trophozoites and cysts were also found (Itoh et al ., ). In experimental leishmaniasis in rodents or in naturally infected dogs, high levels of Iba‐1 or a high density of microglia were observed in the prefrontal cortex or in the ependymal/subependymal areas, respectively (Melo & Machado, ; Portes et al ., ).…”

Pathogenic free‐living amoebic encephalitis in Japan

“…Additionally, successfully treated cases outside of Japan required the administration of multiple drugs, such as pentamidine, macrolide antibiotics, sulfadiazine, and phenothiazine compounds, over several months to several years; however, a recommended treatment has not been established. 1,4,16 In GAE caused by Acanthamoeba spp., there is no standard treatment due to the variable sensitivity of amoebas isolated from each patient. Moreover, there are few cases of successful treatment of GAE associated with Acanthamoeba spp.…”

An Acute Case of Granulomatous Amoebic Encephalitis-<i>Balamuthia mandrillaris</i> Infection

“…This is one of the reasons why a definitive diagnosis is difficult before patient death. Neuroimaging typically reveals multiple patchy lesions with hemorrhaging ( 4 ) exhibiting high intensity on diffusion-weighted imaging and ringed enhancement on T1-weighted imaging. Our case had multiple small lesions with ringed enhancement on T1-weighted imaging around the lateral ventricles ( Fig.…”

“…The highest prevalence of cases has been observed in temperate regions in the southern areas of North America and Latin America ( 2 , 3 ). Nine cases of CNS infection due to B. mandrillaris have been reported in Japan ( 4 , 5 ). Although only 3 cases were reported in the 23 years between 1986 and 2009 (the first case in 1986 was retrospectively diagnosed as a case of B. mandrillaris infection), infections have been reported almost every year since 2010.…”