Agglutination of Naegleria fowleri by human serum.

Abstract The capability of 154 serum samples from pediatric outpatients and 101 samples from adults to agglutinate amoebae of Naegleria fowleri nN68 was assessed. Sera from all 19 infants tested had an agglutination titer of 1:4 or less; sera of toddlers had a median agglutination titer of 1:8 and those of adults, 1:16. Only 13 of 154 serum samples from children had titers of 1:32 or 1:64; 7 of these high titered sera were from the 38 asthmatic children. Selected sera were found to give comparable titers when assayed against eight other strains of N. fowleri. Agglutination activity was removed by absorption with N. fowleri but not by absorption with N. gruberi. The agglutinating activity was specific for the human pathogenic N. fowleri. The ubiquitous free-living N. gruberi was not the immunogen responsible for the agglutinating activity in human serum.