ISOLATION, IDENTIFICATION AND INCREASING IMPORTANCE OF FREE-LIVING AMEBAS CAUSING HUMAN-DISEASE

Amphizoic small amoebic protozoa are capable of existing both in `free -living' and in `parasitic' form depending on the actual conditions. T wo genera (Naegleria and Acanthamoeba) have become recognised as oppor tunist human parasites. Since the first description in 1965 of a letha l case of primary amoebic meningoencephalitis (PAM) caused by Naegleri a, many more (mostly lethal) cases have been reported, while granuloma tous amoebic encephalitis (GAE), as well as eye (keratinitis, conjunct ivitis, etc.), ear, nose, skin and internal organ infections caused by Acanthamoeba have also occurred in rapidly increasing numbers. Both p athogenic and non-pathogenic species of Naegleria and Acanthamoeba are found worldwide in water, soil and dust, where they provide a potenti al source of infection. Successful differential diagnosis and appropri ate (specific) therapy depends on precise laboratory identification of the `free-living' amoebae. In most cases, isolation from the environm ent can be achieved, but identification and differentiation of the pat hogenic and non-pathogenic strains is not easy. The methods presently available do not fulfil completely the requirements for specificity, s ensitivity and reliability. Morphological criteria are inadequate, whi le thermophilic character, pH dependency and even virulence in infecte d mice, are not unambiguous features of pathogenicity of the different strains. More promising are molecular methods, such as restriction en donuclease digestion of whole-cell DNA or mitochondrial DNA, as well a s iso-enzyme profile analysis after iso-electric focusing and staining for acid phosphatase and propionyl esterase activity. Use of appropri ate monoclonal antibodies has also yielded promising results in the di fferentiation of human pathogenic and non-pathogenic strains. However, quicker, simpler, more specific and reliable methods are still highly desirable. The significance of endosymbiosis (especially with Legione lla strains) is not well understood. The results of a systematic surve y in Hungary for the isolation and identification of `free-living' amo ebae, including an investigation of the Hungarian amoebic fauna, the i solation of possibly pathogenic Naegleria strains and of some Acantham oeba strains from eye diseases, as well as the finding of a case of en dosymbiosis, are also reported here.