Opportunistic Free-living Amebae, Part I¹

Abstract 

The free-living amebae Acanthamoeba spp., Balamuthia mandrillaris, and Naegleria fowleri have been recognized as etiologic agents of amebic encephalitis. Although each has its own morphologic, ecologic, and epidemiologic traits, they have in common the ability to tolerate mammalian body temperature and cause infections. The amebic diseases are difficult to diagnose clinically, leading to delay in treatment, resulting in a high mortality rate. The major tests for the diagnosis of these diseases include immunostaining for amebae in brain and other tissues and conventional and real-time PCR. Because the number of reported cases is low, only a handful of laboratories are equipped for performing such testing. Acanthamoeba causes systemic infections mainly in immunocompromised individuals but can also cause corneal infections in healthy individuals who wear contact lenses. In Part I of this article, the general characteristics of Acanthamoeba are reviewed, as well as its cultivation, the diseases it causes, the pathophysiology of infections, mechanisms of pathogenesis, therapy and prognosis, and, finally, prevention and control. In addition, the general characteristics of B. mandrillaris, which causes a subacute though deadly infection in either healthy or immunocompromised hosts, is discussed.

• 1 Editor's Note: Part II of this article will be published in the November 1, 2008 issue of CMN (Vol. 30, No. 21).