AWWA WQTC65823

This paper discusses a study of three different amebae, including their biology, epidemiology and public health significance. Among the hundreds of small free-living amebae that exist in nature only three different amebae belonging to the genera Acanthamoeba, Balamuthia and Naegleria, have been identified as agents of central nervous system (CNS) infections of humans and other animals. Several species of Acanthamoeba (e.g., A. castellanii, A. culbertsoni, A. hatchetti, A. healyi, A. polyphaga, A. rhysodes, and A. divionensis) and the only known species of Balamuthia, B. mandrillaris, are known to cause a subacute and chronic disease, granulomatous amebic encephalitis (GAE). Although more than 30 species of Naegleria have been described, only one species, Naegleria fowleri, is known to cause an acute, fulminating disease, primary amebic meningoencephalitis (PAM). Acanthamoeba spp. also causes infection of the human cornea, Acanthamoeba keratitis. Additionally, both Acanthamoeba spp. and B. mandrillaris have been identified as agents of cutaneous infections in humans. Both N. fowleri and Acanthamoeba spp. are commonly found in soil, freshwater, sewage and sludge, and even dust in air. They feed on bacteria and multiply in their environmental niche as free-living organisms. Several species of Acanthamoeba have also been isolated from brackish water and seawater and from ear discharge, pulmonary secretions, nasopharyngeal mucosa samples, maxillary sinus samples, mandibular autografts, and stool samples. Acanthamoeba spp. have also been known to host bacterial pathogens such as Legionella spp., Mycobacterium avium, Listeria monocytogenes, Burkholderia pseudomallei, Vibrio cholerae, and Escherichia coli serotype O157, which indicates the public health importance of these amebae. Balamuthia mandrillaris, the only species that has been described so far, has been isolated from human and animal brains and only recently has it been isolated from soil and hence not much is available on the environmental niche of this ameba and its feeding habits. The concept that these small free-living amebae could cause infections in humans was developed by Culbertson and colleagues, who isolated Acanthamoeba sp., strain A-1 (now designated Acanthamoeba culbertsoni) from tissue culture medium thought to contain an unknown simian virus. They also demonstrated amebae in brain lesions of mice and monkeys that died within a week after intracerebral inoculation with this strain. In 1965, Fowler and Carter identified for the first time a fatal infection due to free-living amebae in the brain of an Australian patient which they thought was Acanthamoeba but now it is now believed to have been due to Naegleria fowleri. Includes 14 references, figures.