56 - Pathogenic and Opportunistic Free-Living Amoebae: Agents of Human and Animal Disease

Abstract

Acanthamoeba, Balamuthia, and Naegleria are three genera of free-living amoebae (FLA) found in the natural environment (in the case of Acanthamoeba, also in man-made environments) that are capable of causing devastating central nervous system (CNS) infections and have been reported worldwide. Acanthamoeba spp. cause chronic granulomatous amoebic encephalitis (GAE) usually in immunocompromised hosts and Balamuthia mandrillaris cause GAE in both immunocompetent and immunocompromised hosts who may have a history of exposure to soil. Naegleria fowleri directly invade the CNS causing acute primary amoebic meningoencephalitis (PAM) in apparently healthy children and young adults with recent exposure to warm, fresh water. CNS infections with FLA are under-reported and under-diagnosed globally due to a low index of suspicion, similarity in presentation to other CNS lesions including viral and bacterial infections and the lack of availability of appropriate diagnostics. They have a high case fatality rate even when diagnosed and treatment instituted early. Recently, therapeutic recommendations for PAM using multiple drugs and supportive measures based on reports of survivors have been published. For GAE due to Acanthamoeba spp. and Balamuthia, drug recommendations based on reports of successful treatment are available but dosage and duration of treatment vary. Acanthamoeba also causes severe, refractory keratitis usually following trauma and in contact lens users. Prevention of infection is difficult due to the ubiquitous nature of these parasites.