No abstract

Comparative studies were conducted on the structure, nutrition, protein composition, immunology, and effect on cell cultures of Acanthamoeba sp. (Lilly A-1 strain), A. castellanii (Singh and Neff strains), A. astronyxis, A. comandoni, A. polyphaga, A. terricola, Hartmannella vermiformis, and Naegleria gruberi. Lilly A-1 strain of Acanthamoeba received special attention owing to its pathogenicity for experimental animals. Distinct differences were noted in structure, nutrition, and antigenic composition of Acanthamoeba spp. and Hartmannella, and it was concluded that their recognition as separate genera is justified. With the exception of A. terricola, all species of Acanthamoeba could be differentiated by cyst structure. Cysts of A. terricola closely resembled those of A. castellanii Singh strain, and close antigenic relationships between these 2 species were demonstrated by gel diffusion and immunoelectrophoresis (IEP); it was concluded that the 2 amebae belong in the same species. The pathogenic Acanthamoeba sp, Lilly strain differed from the nonpathogenic A. castellanii Singh strain (a) cyst structure; (b) protein distribution patterns (on disc electrophoresis);(c)soluble and particulate antigens (on gel diffusion, IEP, complement fixation, and immobilization tests); (d) capacity to induce cell-free plaques and other cytopathic effect (CPE) in mammalian monlayer cell cultures; (e) elimination of a phospholipase, responsible for some of the CPE, into the culture medium. Acanthamoeba sp. Lilly strain, which liberated more phospholipase, produced more CPE. Acanthamoeba sp. Lilly strain differed also from other species of this genus in cyst structure and antigenic composition. It was concluded, therefore, that, following the recommendation of Singh & Das, it ought to be placed in a separate species, Acanthamoeba culbertsoni.

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Balamuthia mandrillaris is a newly described free-living amoeba capable of causing fatal meningoencephalitis in humans and animals. Because the number of human cases is rapidly increasing, this infection is now considered an important emerging disease by the medical community. A retrospective review of the pathology database for the Zoological Society of San Diego (the San Diego Zoo and San Diego Wild Animal Park) for the period July 1965 through December 1994 revealed five cases of amoebic meningoencephalitis, all in Old World primates. The infected animals were a 3-year, 10-month-old female mandrill (Papio sphinx), from which the original isolation of B. mandrillaris was made, a 5-year-old male white-cheeked gibbon (Hylobates concolor leucogenys), a 1-year-old female western lowland gorilla (Gorilla gorilla gorilla), a 13-year, 5-month-old male western lowland gorilla, and a 6-year-old female Kikuyu colobus monkey (Colobus guereza kikuyuensis). Two different disease patterns were identified: the gibbon, mandrill, and 1-year-old gorilla had an acute to subacute necrotizing amoebic meningoencephalitis with a short clinical course, and the adult gorilla and colobus monkey had a granulomatous amoebic meningoencephalitis with extraneural fibrogranulomatous inflammatory lesions and a long clinical course. Indirect immunofluorescent staining of amoebas in brain sections with a Balamuthia-specific polyclonal antibody was positive in all five animals. Indirect immunofluorescent staining for several species of Acanthamoeba, Naegleria fowleri, and Hartmanella vermiformis was negative. Direct examination of water and soil samples from the gorilla and former mandrill enclosures revealed unidentified amoebas in 11/27 samples, but intraperitoneal inoculations in mice failed to induce disease. Attempts to isolate amoebas from frozen tissues from the adult male gorilla were unsuccessful.

Balamuthia mandrillaris, formerly referred to as a leptomyxid ameba, is a free-living ameba that has recently been identified as a cause of meningoencephalitis. Previously, only two genera, Naegleria and Acanthamoeba, were recognized as causes of central nervous system (CNS) infections in humans. In contrast to Naegleria, Balamuthia causes a subacute-to-chronic infection of the CNS. Distinct from Acanthamoeba, which appears to favor the immunocompromised host, Balamuthia is capable of infecting both healthy and immunosuppressed hosts. Retrospective analyses as well as an accumulation of newly identified cases have demonstrated that this ameba is an increasingly important pathogen to recognize. We report the isolation, histopathologic features, and confirmation by indirect immunofluorescence of B. mandrillaris in a case of fatal amebic meningoencephalitis.