Free-Living Amoebae Infections: Case Reports Identified at a Reference Parasitology Laboratory in Argentina

To document cases of free-living amoebae (FLA) infections in humans diagnosed at a Reference Parasitology Laboratory in Argentina, contributing to the epidemiological understanding of these infections in the country.

A retrospective analysis was performed on 43 samples from suspected cases of FLA infection collected between October 2022 and June 2025. The samples included 4 ocular specimens, 20 brain biopsies, 12 cerebrospinal fluid samples, 6 skin biopsies, and 1 liver biopsy. FLA culture was carried out only in suspected keratitis cases, using liquid Page's solution supplemented with fresh Escherichia coli culture. In all cases, multiplex real-time PCR (qPCR) was employed for the simultaneous detection of Acanthamoeba spp., Naegleria fowleri, and Balamuthia mandrillaris. The cases were analyzed together with the information provided in the epidemiological forms that accompanied the samples.

Of the 43 analyzed samples from suspected cases, 5 tested positive (11.6%), including 1 case of keratitis caused by Acanthamoeba spp. and 4 cases of granulomatous amebic encephalitis (GAE) due to B. mandrillaris. The GAE cases involved immunocompetent children and one adult with a functional immunosuppression risk factor (chronic alcoholism). One patient presented with chronic skin lesions prior to the CNS infection, and another case involved co-infection with Toxoplasma gondii. Neuroimaging in all GAE patients showed lesions consistent with mass or infectious processes, and brain biopsy samples were essential for diagnosis. Two of the GAE patients survived following combined therapy.

Infections caused by FLA are rare but highly severe, particularly non-keratitis presentations. Early clinical suspicion, rapid and accurate diagnosis, and aggressive treatment are crucial to improving patient outcomes.