[A study on transmission of bancroftian filariasis in Tancheng county, South Shandong province].

A longitudinal study was conducted to explore transmission dynamics and epidemic trend of bancroftian filariasis in Huayuan Village, Shengli Township, Tancheng County, Shandong Province, a previous highly endemic area of it, from 1984, the fifth year after its preliminary eradication, to 1993, without any control measures being taken. Results showed proportions of residents with microfilaremia decreased to 0.12% in 1993 from 0.56% before the study. Eight of the nine microfilaria carriers before the study became negative spontaneously. Six new microfilaria carriers were detected during the study period, but five of them converted negative in three or four years. Negative conversion rate of blood IgG4 in microfilaremia cases was 88.89% by the end of the study. Natural infection rate in mosquitoes dropped year by year, with 0.21%, 0.19% and 0.06% for 1984, 1985 and 1986, respectively, and no filarial larvae was found in them in 1993 and natural transmission potential dropped from 3.47 to zero. It suggested the threshold for transmission of filariasis was not reached and the transmission was close to the end, with the rates of mosquito biting of 24.1-52.5 and 13.5-21.0 times per person, per night, for those using or non-using mosquito net, respectively.