Pathogenic free‐living amoebic encephalitis in 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.

Fatal granulomatous amoebic encephalitis due to free‐living amoebae in two boys in two different hospitals in Lima, Perú

“…Amoebic infections of the central nervous system (CNS) are very rare, and usually fatal. Two main forms of CNS infection caused by free‐living amoebae (FLA) are recognized: (i) primary amoebic meningoencephalitis (PAM) due to Naegleria fowleri ; (ii) granulomatous amoebic meningoencephalitis caused by Acantamoeba spp., Balamuthia mandrillaris , and the recently recognized Sappinia pedata …”

“…Two main forms of CNS infection caused by free-living amoebae (FLA) are recognized: (i) primary amoebic meningoencephalitis (PAM) due to Naegleria fowleri; (ii) granulomatous amoebic meningoencephalitis caused by Acantamoeba spp., Balamuthia mandrillaris, and the recently recognized Sappinia pedata. [1][2][3] To report the fatal outcome of two patients with FLA infections, treated with combination regimens for bacterial meningoencephalitis. In both cases a brain biopsy was performed, the histology confirmed granulomatous amoebic encephalitis with the presence of amoebic trophozoites and occasional cysts.…”

A Japanese case of amoebic meningoencephalitis initially diagnosed by cerebrospinal fluid cytology

“…Parasitic amoebae feed on other animals, and Entamoeba histolytica in particular is known to cause amoebic dysentery in humans. Among free‐living amoebae, more than 200 types are present in the soil and water in nature 1 . While these protozoans have previously not been considered to be pathogenic in humans, 1,2 some have recently been shown to actually be parasites; 1‐3 for example, Acanthamoeba spp.…”

“…Among free‐living amoebae, more than 200 types are present in the soil and water in nature 1 . While these protozoans have previously not been considered to be pathogenic in humans, 1,2 some have recently been shown to actually be parasites; 1‐3 for example, Acanthamoeba spp. causes amoebic keratitis, and B mandrillaris , Acanthamoeba spp., and Naegleria fowleri cause encephalitis.…”

“…Because the fatality rate of amoebic encephalitis is extremely high, the pathogen is known as the "brain‐eating amoeba. " 4 In Japan, there have been only a few reports of amoebic encephalitis, 5‐9 and the route of infection, detailed clinical manifestation, and pathogenesis remain unclear 1 …”