Free-living Ameba Infections: Rare but Fatal

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Yaowalark Sukthana



Free-living ameba infections, although rare, are recognized as causes of fatal infection in bothimmunocompetent and immunocompromised persons. Naegleria fowleri causes primary amebicmeningoencephalitis (PAM), which is a rapid and fulminant central nervous system (CNS) infectionin normal hosts. Acanthamoeba causes chronic or subacute granulomatous amebic encephalitis (GAE)in immunosuppressive persons. Balamuthia also causes GAE, but in competent hosts.PAM should be considered in all patients with meningoencephalitis, especially if they have arecent history of swimming in fresh water. A clue that suggests the diagnosis is a negative CSF Gramstain finding in a patient with purulent meningitis.Healthcare providers should be aware of Acanthamoeba as a potential pathogen in the HIV-infectedpatient population. Early diagnosis may allow for prompt intervention and increase a patient’schance of survival.Clinicians, parasitologists, and pathologists must include free-living amebae in the differentialdiagnosis of possible pathogenic agents that cause sinusitis and cutaneous nodules or ulcers, with orwithout CNS involvement, especially when bacteria, fungi, or mycobacteria are not found by smear,biopsy, or culture. Typical motility of trophozoites on fresh examination is a key for diagnosis.Broad pseudopodia movement is typical for Naegleria, and it can turn into temporary flagellatedform. Spiny cytoplasmic projection or acanthopodia is characteristic of Acanthamoeba.Thoughtful history-taking, prompt simple laboratory examination, and awareness can be veryrewarding.

Keywords: Naegleria fowleri, Acanthamoeba spp, Balamuthia spp, PAM, GAE, Thailand

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