Influence of infection with non-filarial helminths on the specificity of serological assays for antifilarial immunoglobulin G4

Serological assays based on the detection of immunoglobulin (Ig) G4 antibodies to crude filarial extracts are widely used for epidemiological and diagnostic purposes. We tested 195 samples collected in 1998 from an area of Brazil where filariasis is not endemic and 13 (6.7%) had levels of antifilarial IgG4 antibodies that were defined as positive. Both Strongyloides infection and the presence of Strongyloides antibody responses were associated with higher antifilarial antibody responses. None of the specimens had a positive response to the Brugia malayi recombinant antigen (Bm14). These data suggest that serodiagnostic assays based on the use of crude filarial antigens should be interpreted with caution because of the potential for cross-reactivity with Strongyloides.