Changes in anti-filarial antibody after control of filariasis in Shandong Province.

The changes in anti-filarial antibody level at different periods in different population groups of various controlled areas were studied by indirect fluorescent antibody test (IFT) using frozen sections of Brugia malayi adult worms as antigen. The positive rates by IFAT in formerly hyper-, moderate- and low-endemic areas decreased to the level as those in non-endemic areas 15, 10 and 10 years respectively after the control of filariasis. In the children born after the control of filariasis, the IFAT positive rate was less than 1%. An analysis of IFAT positive cases showed that the positive rate was lowest in children under 10 years old and highest in those aged 20-40 and decreased progressively with the increasing of age. In addition, the IFAT positive rates of microfilaremia cases, the residents in currently endemic area and control group from non-endemic area were 91.4%, 33.9% and 4.5% respectively. These data demonstrated the present distribution pattern of anti-filarial antibody.