USE OF ANTIFILARIAL IGG4-ELISA TO DETECT BRUGIA-MALAYI INFECTION IN AN ENDEMIC AREA OF MALAYSIA

OBJECTIVE To evaluate the usefulness of antifilarial IgG4 antibody ass ay in detecting B. malayi infection in a filaria endemic area in Malay sia. METHODS A sandwich ELISA using B. malayi soluble antigen was empl oyed to detect antifilarial IgG4 antibodies in serum samples of 330 in dividuals who comprised 88 healthy individuals from nonendemic areas, 15 B. malayi microfilaraemic cases, 22 individuals with soil-transmitt ed helminthiases, 9 elephantiasis cases and 196 residents from a B. ma layi-endemic area. An O.D. value of > 0.420 at serum dilution of 1:400 was used as the cut-off point. This cut-off point was obtained by tak ing the mean optical density (0.252 + 4 S.E.) of 36 negative sera whic h had O.D. values greater than 0.1 at serum dilution of 1: 400. RESULT S All 15 microfilaraemic persons were positive for antifilarial IgG4 a ntibody. Non-endemic normals, soil-transmitted helminth infected perso ns and chronic elephantiasis cases were negative for antifilarial IgG4 antibody. Of the 196 individuals from the filaria endemic area, 37 (1 8.8%) demonstrated presence of antifilarial IgG4 antibodies; and only eight individuals (4.1%) were positive for microfilariae. All eight mi crofilaraemic individuals were also positive for antifilarial IgG4 ant ibodies. CONCLUSION Antifilarial IgG4-ELISA could detect 4.6 rimes mor e positive cases than the microfilaria detection method. With appropri ate cut-off values that eliminate cross-reactivities, this serological cool is very useful for Brugia malayi prevalence surveys and diagnosi s.