Epidemiological surveillance of filariasis after its control in Shandong Province, China.

Shandong Province used to be the highly endemic area of Wuchereria bancrofti. Culex pipiens pallens was the main mosquito vector. After about 30 years of large scale anti-filariasis control campaign, filariasis was controlled throughout the province in 1983. Since then, extensive cross-sectional and consecutive longtitudinal surveillances have been carried out. Parasitological and entomological data indicated that the microfilaremia rate of the human population, and the natural infection rate of mosquito vector kept declining, with many villages dropping to zero; no children under ten were infected. Serological surveillance showed that antifilarial antibody had fallen to the same level as that in non-endemic areas 10-15 years after control. In addition, patients with chronic manifestations were reduced in number. It is suggested that the achievement in filariasis control in Shandong Province is stable: the transmission of filariasis has been interrupted. However, there are still a few residual microfilaremia cases, which may bring about new infection under conditions favorable for transmission. Infectious sources may be introduced by population movements from a neighboring province where filariasis is still endemic at present. Moreover, new cases with chronic manifestations, especially chyluria, continually emerge. So systematic surveillance should be continued and proper control measures must be taken to eventually wipe the disease out of the province.