Martinez A J, Visvesvara G S
University of Pittsburgh School of Medicine, Neuropathologist, Pathology Department (Neuropathology), Presbyterian University Hospital, Pittsburgh, PA 15213, USA.
Brain Pathol. 1997 Jan;7(1):583-98. doi: 10.1111/j.1750-3639.1997.tb01076.x.
Amebas belonging to the genera Naegleria, Acanthamoeba and Balamuthia are free-living, amphizoic and opportunistic protozoa that are ubiquitous in nature. These amebas are found in soil, water and air samples from all over the world. Human infection due to these amebas involving brain, skin, lung and eyes has increased significantly during the last 10 years. The epidemiology, immunology, protozoology, pathology, and clinical features of the infections produced by these protozoa differ strikingly. Infection by the pathogenic Naegleria fowleri is acquired by exposure to polluted water in ponds, swimming pools and man-made lakes. Raised temperatures during the hot summer months or warm water from power plants facilitate the growth of N. fowleri. N. fowleri is a thermophilic ameba that grows well in tropical and subtropical climates. The CNS infection, called Primary Amebic Meningoencephalitis (PAM), produced by N. fowleri is characterized by an acute fulminant meningoencephalitis leading to death 3-7 days after exposure. Victims are healthy, young individuals with a history of recent water-related sport activities. The portal of entry is the olfactory neuroepithelium. The pathologic changes are an acute hemorrhagic necrotizing meningoencephalitis with modest purulent exudate, mainly at the base of the brain, brain-stem and cerebellum. Trophozoites can be seen within the CNS lesions located mainly around blood vessels. Thus far 179 cases have been reported; 81 in the USA alone. Balamuthia mandrillaris and several species of Acanthamoeba are pathogenic "opportunistic" free-living amebas which cause Granulomatous Amebic Encephalitis (GAE) in humans and animals. GAE is an infection, usually seen in debilitated, malnourished individuals, in patients undergoing immunosuppressive therapy for organ transplants and in Acquired Immunodeficiency Syndrome (AIDS). The granulomatous component is negligible, particularly in immunocompromised individuals. Pathologically these amebas produce a patchy, chronic or subacute granulomatous encephalitis with the presence of trophozoites and cysts. The portal of entry is probably through the respiratory tract or an ulceration of the skin reaching the CNS by hematogenous spread. As of October 1, 1996, 166 cases (103 due to Acanthamoeba and 63 due to Balamuthia) of GAE have been reported from around the world. Of these 103 cases due to Acanthamoeba (72 have been reported in the USA alone, > 50 in AIDS). It is well known that several species of Acanthamoeba can also produce, chronic sight threatening ulceration of the cornea called Acanthamoeba keratitis (AK), mostly in contact lens wearers or in individuals with minor corneal abrasions. Hundreds of cases of AK have been documented world wide.
耐格里属、棘阿米巴属和巴拉姆希阿米巴属的阿米巴原虫是自由生活、兼性寄生和机会性致病的原生动物，在自然界中广泛存在。这些阿米巴原虫存在于世界各地的土壤、水和空气样本中。在过去10年中，由这些阿米巴原虫引起的累及脑、皮肤、肺和眼睛的人类感染显著增加。这些原生动物所引发感染的流行病学、免疫学、原生动物学、病理学和临床特征差异显著。致病性福氏耐格里阿米巴的感染是通过接触池塘、游泳池和人工湖中的污染水而获得的。炎热夏季的高温或发电厂排出的温水有利于福氏耐格里阿米巴的生长。福氏耐格里阿米巴是一种嗜热阿米巴，在热带和亚热带气候中生长良好。由福氏耐格里阿米巴引起的中枢神经系统感染，称为原发性阿米巴脑膜脑炎（PAM），其特征是急性暴发性脑膜脑炎，在接触后3至7天导致死亡。受害者多为健康的年轻人，近期有与水相关的体育活动史。感染途径是嗅神经上皮。病理变化为急性出血性坏死性脑膜脑炎，伴有少量脓性渗出物，主要位于脑底部、脑干和小脑。在主要位于血管周围的中枢神经系统病变内可见滋养体。迄今为止，已报告179例病例；仅在美国就有81例。曼氏巴拉姆希阿米巴和几种棘阿米巴属是致病性“机会性”自由生活阿米巴，可在人和动物中引起肉芽肿性阿米巴脑炎（GAE）。GAE是一种感染，通常见于身体虚弱或营养不良的个体、接受器官移植免疫抑制治疗的患者以及获得性免疫缺陷综合征（AIDS）患者。肉芽肿成分可忽略不计，尤其是在免疫功能低下的个体中。从病理上看，这些阿米巴原虫会引发散在的慢性或亚急性肉芽肿性脑炎，并伴有滋养体和包囊。感染途径可能是通过呼吸道或皮肤溃疡，经血液传播到达中枢神经系统。截至1996年10月1日，世界各地已报告166例GAE病例（103例由棘阿米巴属引起，63例由巴拉姆希阿米巴引起）。在这103例由棘阿米巴属引起的病例中（仅在美国就报告了72例，其中超过50例发生在艾滋病患者中）。众所周知，几种棘阿米巴属还可引起慢性威胁视力的角膜溃疡，称为棘阿米巴角膜炎（AK），主要发生在佩戴隐形眼镜者或有轻微角膜擦伤的个体中。全世界已记录了数百例AK病例。
