Detection of Antibodies against Free-Living Amoebae Balamuthia mandrillaris and Acanthamoeba Species in a Population of Patients with Encephalitis

Background. Balamuthia mandrillaris and Acanthamoeba species are 2 free-living amoebae responsible for granulomatous amoebic encephalitis in humans and animals. We have screened serum samples from hospitalized patients with encephalitis for antibodies against these 2 amoebae as a means of detecting a disease with few defining symptoms and a poor prognosis. Methods. Indirect immunofluorescence antibody (IFA) staining of serum samples from patients with encephalitis was conducted over a period of 6 years to detect amoeba antibodies. More than 250 serum samples from patients hospitalized with encephalitis were screened. Most of the samples were from patients in California and were screened as part of the California Encephalitis Project, with a small number of specimens from other states. Results. During the course of the study, 7 cases of Balamuthia encephalitis were detected; all cases were detected in Hispanic individuals, and all cases were fatal. Examination of hematoxylin-eosin—stained and immunostained sections of brain tissue obtained at biopsy or autopsy for amoebae confirmed balamuthiasis in all serum samples with positive IFA results. One case of Acanthamoeba encephalitis was detected in an immunocompromised individual with a normal antibody titer by identification of amoebae in immunostained brain tissue obtained at autopsy. Conclusions. IFA can be successfully used in screening for balamuthiasis and acanthamoebiasis in patients whose clinical presentation, laboratory results, and neuroimaging findings are suggestive of amoebic encephalitis. Ideally, this can lead to an earlier definitive diagnosis and earlier start of antimicrobial therapy. Without IFA staining, the balamuthiasis cases in our study would have been diagnosed as neurocysticercosis, tumor, tuberculosis, or viral encephalitis or would have been undiagnosed.