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

Soluble antigens from an axenic culture of Entamoeba histolytica were used to develop a commercial ELISA kit to quantify anti-E. histolytica antibodies in sera of patients with extraintestinal amebiasis in non-endemic settings. The diagnostic specificity and sensitivity of the test were assessed retrospectively using 131 human serum samples with amoebic serologic status available. They were selected according to their results in immunofluorescence (IFAT) and were separated in 2 sample categories: 64 sera with positive results by IFAT and 67 with negative results by IFAT. The sensitivity and specificity of the ELISA kit were assessed at 95.0% and 94.0% compared to the IFAT. The test can be useful to exclude a potential diagnosis of amebiasis and could be used as a screening method since ELISA is an automated technique.
Amebiasis ; Antibodies ; Axenic Culture ; Diagnosis ; Entamoeba histolytica ; Enzyme-Linked Immunosorbent Assay ; Fluorescent Antibody Technique ; Humans ; Mass Screening ; Methods ; Retrospective Studies ; Sensitivity and Specificity ; Serologic Tests

PURPOSE: Acute gastroenteritis (AGE) is a major cause of morbidity and remains a major cause of hospitalization. Following the Syrian refugee crisis and insufficient clean water in the region, this study reviews the etiological and epidemiological data in Lebanon. METHODS: We prospectively analyzed demographic, clinical and routine laboratory data of 198 children from the age of 1 month to 10 years old who were admitted with the diagnosis of AGE to a private tertiary care hospital located in the district of Nabatieh in south Lebanon. RESULTS: Males had a higher incidence of AGE (57.1%). Pathogens were detected in 57.6% (n=114) of admitted patients, among them single pathogens were found in 51.0% (n=101) of cases that consisted of: Entamoeba histolytica 26.3% (n=52), rotavirus 18.7% (n=37), adenovirus 6.1% (n=12) and mixed co-pathogens found in 6.6% (n=13). Breast-fed children were significantly less prone to rotavirus (p=0.041). Moreover, children who had received the rotavirus vaccine were significantly less prone to rotavirus (p=0.032). CONCLUSION: Our findings highlight the high prevalence of E. histolytica infection as the major cause of pediatric gastroenteritis in hospitalized children, during the summer period likely reflecting the insanitary water supplies and lack of hygiene. Moreover the 42.4% of unidentified causative pathogens should prompt us to widen our diagnostic laboratory arsenal by adopting new diagnostic technologies.
Adenoviridae ; Amebiasis ; Child ; Child, Hospitalized* ; Diagnosis ; Diarrhea ; Entamoeba histolytica ; Gastroenteritis* ; Hospitalization ; Humans ; Hygiene ; Incidence ; Lebanon* ; Male ; Prevalence ; Prospective Studies ; Refugees ; Rotavirus ; Tertiary Healthcare ; Water ; Water Supply

Amebic liver abscess (ALA) is the most common extraintestinal manifestation of amebiasis. Amebiasis, a parasitic infection caused by Entamoeba histolytica, used to be a prevalent protozoan disease in Korea, however, with an improving sanitary system, it has been among very uncommon etiology of liver abscess. A recent report suggested that ALA is an emerging parasitic infection in human immunodeficiency virus (HIV)-infected patients even in areas where the disease is not endemic and recommended HIV screening in patients in areas where ALA is not endemic, particularly those without history of travel to a disease-endemic area. We report on two patients who were admitted for treatment of ALA and then diagnosed as HIV infection. We also reviewed the etiology and characteristics of ALA in our hospital during the last 5 years.
Amebiasis ; Diagnosis* ; Entamoeba histolytica ; HIV Infections ; HIV* ; Humans* ; Korea ; Liver Abscess ; Liver Abscess, Amebic* ; Mass Screening

Amebic liver abscess (ALA) is the most common extraintestinal manifestation of amebiasis. Amebiasis, a parasitic infection caused by Entamoeba histolytica, used to be a prevalent protozoan disease in Korea, however, with an improving sanitary system, it has been among very uncommon etiology of liver abscess. A recent report suggested that ALA is an emerging parasitic infection in human immunodeficiency virus (HIV)-infected patients even in areas where the disease is not endemic and recommended HIV screening in patients in areas where ALA is not endemic, particularly those without history of travel to a disease-endemic area. We report on two patients who were admitted for treatment of ALA and then diagnosed as HIV infection. We also reviewed the etiology and characteristics of ALA in our hospital during the last 5 years.
Amebiasis ; Diagnosis ; Entamoeba histolytica ; HIV Infections ; HIV ; Humans ; Korea ; Liver Abscess ; Liver Abscess, Amebic ; Mass Screening

Acanthamoeba cysts are resistant to unfavorable physiological conditions and various disinfectants. Acanthamoeba cysts have 2 walls containing various sugar moieties, and in particular, one third of the inner wall is composed of cellulose. In this study, it has been shown that down-regulation of cellulose synthase by small interfering RNA (siRNA) significantly inhibits the formation of mature Acanthamoeba castellanii cysts. Calcofluor white staining and transmission electron microscopy revealed that siRNA transfected amoeba failed to form an inner wall during encystation and thus are likely to be more vulnerable. In addition, the expression of xylose isomerase, which is involved in cyst wall formation, was not altered in cellulose synthase down-regulated amoeba, indicating that cellulose synthase is a crucial factor for inner wall formation by Acanthamoeba during encystation.
Acanthamoeba castellanii/*enzymology/genetics/metabolism ; Aldose-Ketose Isomerases/*biosynthesis ; Amebiasis/*pathology ; Benzenesulfonates ; Cell Wall/chemistry/genetics/*metabolism ; Cellulose/biosynthesis ; Down-Regulation ; Encephalitis/parasitology ; Glucosyltransferases/*biosynthesis/genetics ; Keratitis/parasitology ; Microscopy, Electron, Transmission ; RNA Interference ; RNA, Small Interfering

After bathing at a hot spring resort, a 75-year-old man presented to the emergency department because of seizure-like attack with loss of conscious. This is the first case of primary amebic meningoencephalitis (PAM) caused by Naegleria fowleri in Taiwan. PAM was diagnosed based on detection of actively motile trophozoites in cerebrospinal fluid using a wet-mount smear and the Liu's stain. The amoebae were further confirmed by PCR and gene sequencing. In spite of administering amphotericin B treatment, the patient died 25 days later.
Aged ; Amebiasis/*diagnosis/parasitology/*pathology ; Central Nervous System Protozoal Infections/*diagnosis/parasitology/*pathology ; Cerebrospinal Fluid/parasitology ; DNA, Protozoan/chemistry/genetics ; Fatal Outcome ; Humans ; Male ; Microscopy ; Naegleria fowleri/classification/genetics/*isolation & purification ; Polymerase Chain Reaction ; Sequence Analysis, DNA ; Taiwan

Autophagy-related protein 8 (Atg8) is an essential component of autophagy formation and encystment of cyst-forming parasites, and some protozoa, such as, Acanthamoeba, Entamoeba, and Dictyostelium, have been reported to possess a type of Atg8. In this study, an isoform of Atg8 was identified and characterized in Acanthamoeba castellanii (AcAtg8b). AcAtg8b protein was found to encode 132 amino acids and to be longer than AcAtg8 protein, which encoded 117 amino acids. Real-time PCR analysis showed high expression levels of AcAtg8b and AcAtg8 during encystation. Fluorescence microscopy demonstrated that AcAtg8b is involved in the formation of the autophagosomal membrane. Chemically synthesized siRNA against AcAtg8b reduced the encystation efficiency of Acanthamoeba, confirming that AcAtg8b, like AcAtg8, is an essential component of cyst formation in Acanthamoeba. Our findings suggest that Acanthamoeba has doubled the number of Atg8 gene copies to ensure the successful encystation for survival when 1 copy is lost. These 2 types of Atg8 identified in Acanthamoeba provide important information regarding autophagy formation, encystation mechanism, and survival of primitive, cyst-forming protozoan parasites.
Acanthamoeba castellanii/cytology/*genetics/physiology ; Amebiasis/*parasitology ; Amino Acid Sequence ; Autophagy ; Cell Membrane/metabolism ; DNA, Protozoan/chemistry/genetics ; Gene Dosage ; Gene Silencing ; Genes, Reporter ; Humans ; Molecular Sequence Data ; Phagosomes/metabolism ; Protein Isoforms ; Protozoan Proteins/*genetics/metabolism ; RNA, Messenger/genetics ; RNA, Protozoan/genetics ; RNA, Small Interfering/chemical synthesis/genetics ; Recombinant Fusion Proteins ; Sequence Alignment

Amebic liver abscess (ALA) has been diagnosed in travelers to endemic areas or in patients with immunosuppression secondary to human immunodeficiency virus infection since the late 1990s. Further, it is a rare disease in Korea. ALA should be considered in patients present with fever and right upper quadrant pain along with a risk of exposure to amebiasis. We report an 82-year-old man with symptoms of fever, gross hematuria and severe renal impairment as having amebic liver abscess complicated with the obstruction of the inferior vena cava. Amebic liver abscess was successfully treated with antibiotics alone. Also, hematuria disappeared and renal dysfunction improved after treatment.
Aged, 80 and over ; Amebiasis ; Anti-Bacterial Agents ; Fever ; Hematuria ; HIV ; Humans ; Immunosuppression ; Korea ; Liver Abscess, Amebic* ; Rare Diseases ; Renal Insufficiency ; Vena Cava, Inferior*

Acanthamoeba spp. are single-celled protozoan organisms that are widely distributed in the environment. In this study, to understand functional roles of a mannose-binding protein (MBP), Acanthamoeba castellanii was treated with methyl-alpha-D-mannopyranoside (mannose), and adhesion and cytotoxicity of the amoeba were analyzed. In addition, to understand the association of MBP for amoeba phagocytosis, phagocytosis assay was analyzed using non-pathogenic bacterium, Escherichia coli K12. Amoebae treated with mannose for 20 cycles exhibited larger vacuoles occupying the most area of the amoebic cytoplasm in comparison with the control group amoebae and glucose-treated amoebae. Mannose-selected amoebae exhibited lower levels of binding to Chinese hamster ovary (CHO) cells. Exogenous mannose inhibited >50% inhibition of amoebae (control group) binding to CHO cells. Moreover, exogenous mannose inhibited amoebae (i.e., man-treated) binding to CHO cells by <15%. Mannose-selected amoebae exhibited significantly decreased cytotoxicity to CHO cells compared with the control group amoebae, 25.1% vs 92.1%. In phagocytic assay, mannose-selected amoebae exhibited significant decreases in bacterial uptake in comparison with the control group, 0.019% vs 0.03% (P<0.05). Taken together, it is suggested that mannose-selected A. castellanii trophozoites should be severely damaged and do not well interact with a target cell via a lectin of MBP.
Acanthamoeba castellanii/drug effects/metabolism/*pathogenicity ; Amebiasis/*parasitology ; Animals ; CHO Cells ; Cell Adhesion/drug effects ; Cell Survival ; Cricetinae ; Cricetulus ; Escherichia coli K12/metabolism ; Female ; Mannose/*pharmacology ; Mannose-Binding Lectin/*metabolism ; Phagocytosis ; Protozoan Proteins/metabolism