Size and charge antigens of Dirofilaria immitis adult worm for IgG-ELISA diagnosis of bancroftian filariasis

Abstract

We used Dirofilaria immitis adult worm antigens to develop an IgG-ELISA, then used this to evaluate 30 serum samples of patients with proven Wuchereria bancrofti infection, 131 samples of patients with other parasitic diseases and 30 serum samples of healthy controls. The D. immitis antigen was prepared using two methods: Sephacryl S-200 chromatography and iso-electric focusing with a Rotofor cell. This was done to determine the best method for diagnosing W. bancrofti filariasis. Before fractionation, crude male D. immitis antigen yielded 100% sensitivity and 60.8% specificity, and crude female antigen yielded 80% sensitivity and 52.8% specificity, respectively, to detect W. bancrofti infection. After gel filtration chromatography, the male D. immitis antigen, called MP1, yielded 100% sensitivity and 95% specificity, and female D. immitis antigen, called FmP1, gave 100% sensitivity and 59.6% specificity, to detect W. bancrofti infection. Using iso-electricfocusing, both male and female crude D. immitis antigens (Iso-MF and Iso-FmF, respectively) were separated mechanically into 20 iso-fractions (F1-F20) each. By preliminary screening with ELISA, using pooled positive and negative sera, Iso-MF10, pH 7.5, and Iso-FmF14, pH 7.6, were selected. Iso-MF10 gave 100% sensitivity and 96.9% specificity, and Iso-FmF14 gave 100% sensitivity and 64% specificity. In the study, Og4C3-ELISA, for the detection of circulating filarial antigen, was also used to analyze these serum samples, it gave 87.6% sensitivity and 99.4% specificity to detect W. bancrofti infection. Male D. immitis antigens, MP1 and Iso-MF10, gave high sensitivity and specificity, and appear to be the best choices for use in an ELISA to diagnose bancroftian filariasis.